Shielding boost converter for RF transceiver - Page 1
Forum section: electronics / projects

author: Buriedcode
author_rank: Super Contributor
timestamp: September 04, 2024, 02:59:59 pm
content: Hi,I have several (ongoing, because I'm lazy) projects that are battery powered from a couple of AA cells, that use RF transceivers and/or recievers. Some with the CC1101, some with the RFM69HCW, and a few general basic 315/433MHz modules.I've noticed that in many cases on my prototypes, the use of a boost converter stepping up the AA cells to 3/3 or 5V will either greatly redice the range of the RF link, or stop it working entirely. I have used an LDO after the boost converter, as well as an inductor/cap filter to power these transceivers, but it is hard to know how well this works - things do seem to improve but nowhere near the performance of when it is powered by a higher voltage battery + linear reg. I'm unsure how much is conducted noise through the power supply, and how much is radiated.So, aside from looking for specialist low noise charge pumps - which aren't all that efficient - do you think it would be worth using a shielding can/RFI shield around the boost converter? The bottom layer will be almost solid ground plane. I'm even considering making up some PCB's to form modules - maybe 10x20mm with a shielding can to attempt to fully enclosure these, with only pins or cestellated holes for connecting VIN/VOUT. I haven't found existing modules that have the right Vin range (2-3V) and relatively low current (<100mA out).I would just switch to a 9V and lienar reg, but I hate PP3, they end to be expensive and less capacity than AA's - which are available pretty much everywhere. I could also go for a lithium pouch cell, but this doesn't really solve the problem since its voltage will still need a converter to provide power over its voltage range.I guess my ain question is - is radiated EMI more of a problem for RF recievers than conducted? We're talking single inductor sychronous boost converters Fsw range 300kHz - 1.2MHz, 2A Ipeak max. Typical single-cell-to-5v types.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 04, 2024, 03:24:36 pm
content: Usually a small low power boost converter is just not big enough to radiate a lot of power by itself in the range <1GHz. But it can conduct a lot of EMI into its cabling and load, which again may be large enough to radiate.That means: The first thing you should try is to place filters in the input and output of the converter. A good start would be a pi-filter in the input and output together with at least one common mode choke - usually at the input side, but if the input is only a small battery it could also be worth to try the common mode choke in the output line.

author: Buriedcode
author_rank: Super Contributor
timestamp: September 04, 2024, 04:25:42 pm
content: Quote from: Phil1977 on September 04, 2024, 03:24:36 pmAs the batteries will often be connected to the PCB with wires - since the enclosure has provisions for AA battery clips, I guess these wires being anthing from 20 to 50mm could be part of the issue. Honestly, it never really occured to be to look at the input even though thats where the high current switching happens.Quote from: Phil1977 on September 04, 2024, 03:24:36 pmI think I'm gonna have to set up a small test bed for this. I might not have the facility to measure EMI, but certain conducted noise, and I could do some basic range checks with different filters at different places.Cheers!

author: Randy222
author_rank: Frequent Contributor
timestamp: September 04, 2024, 04:42:54 pm
content: Can you look at signal on something like tinySA ? "signal" as in actual signal in transmission line, and then clamp onto a piece of metal to see if EMI is there, or even place use a 314-433 antenna on a scope or tinySA placed near your device, see what shows up. Some time ago I notice my Rigol scope has a lot of noise around 1.5MHz. Turns out it's a local AM 1550 station.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 04, 2024, 08:54:57 pm
content: Perhaps more likely is differential noise, supply ripple, modulating the transceiver and mucking up its operation (voltage to frequency modulation i.e. it can't track a signal, or at least as well; amplitude modulation introducing sidebands and inter-channel images; etc.). Higher frequencies may radiate from the device overall, but it's unlikely much harmonics are present in the several-100s-MHz range. But who knows; varying amounts of those factors may all play a role in some configuration or another.You can determine both, by putting the converter on a reference plane -- a solid piece of metal, usually a blank copper-clad PCB to make convenient soldered connections. Put the converter there (whether module, or building a circuit directly on top e.g. Manhattan style), and mind where the connections go:- Ground to plane, of course!- Route input and output together, so they're co-located. If there is voltage drop along the plane, this minimizes how much of that voltage they pick up. Note that, if connections come off opposite ends of a converter module, it's likely there's some (high frequency) voltage drop along it, which thus radiates into the wire pairs (when used as an inline module).- Filter both input and output, with one or two stages of LC filtering. Not much should be required, a couple uF and fractional-uH will suffice for high frequencies. An electrolytic is a good idea as well, to provide ESR to dampen the filter (which otherwise doesn't have much termination resistance around it, which can lead to quite strong frequency peaks that cause problems for the module or connected circuitry).- Note that a filter has a ground connection. This is the reference against which the signals get filtered, i.e. for frequencies above cutoff frequency, they take on this potential instead. You want input and output filters close together, to minimize the voltage between them, and you want them away from (not much straight-line distance is actually needed, just that it's not in the immediate vicinity of) the converter.- Making the converter into a three-terminal module, common ground at a single point, eliminates common mode noise: by definition, there is only input and output (normal mode), there's no ground-to-ground voltage at all (or, it's trivially defined as zero, being the same point).Also, be careful whether the module is common-ground or not. A current-mode buck converter may have an output current sense resistor, and expects an isolated load. You need to filter this separately as its own wire (same as input and output), rather than short it to GND plane.Then you can put a shield over top the ground plane, which can be a few pieces of copper clad soldered together along the seams, to block most electric and magnetic field lines around the converter.Example: a bunch of years ago I built this radio set,https://seventransistorlabs.com/Radio_20m/Images/Radio_Wide.jpgwhich uses a DC-DC converter (top-left) to take 12V and make 6.3V and 120V for the vacuum tube receiver. The converter is contained within the five-sided copper-clad box. The wires exit the open side, wrapping around to the lid where a little extra filtering is provided. The receiver gets clean DC power and no noticeable conducted emissions couple into it; indeed, I can put an inductive loop probe on the antenna jack, and wave it around the converter and receive nothing, but sticking it inside the box picks up many... well, I don't have a measure of intensity, this receiver isn't calibrated, but needless to say the received power goes up by 20s of dB, and the intense crunch of white noise plays through the speaker.Tim

author: Buriedcode
author_rank: Super Contributor
timestamp: September 06, 2024, 03:09:46 am
content: Quote from: Randy222 on September 04, 2024, 04:42:54 pmThat antenna idea sounds interesting - I never really thought of what the reciever "see's" on its antenna, interms of SMPS noise. Whilst not the same modules, I have noticed the fully shielded (as in RFI can) NRF240L01 modules I have are ok with SMPS, providing they have quite large bulk capacitance on their power inputs - where-as the cheaper unshielded ones barely reach 20m. It's not a great comparison because a) 2.4GHz is a different band to the 434/315 and b) two different modules, by different manufacturers, with different layouts isn't exactly apples-to-apples.Quote from: T3sl4co1l on September 04, 2024, 08:54:57 pmYes, this is the thing I'm trying to tease apart - how much is radiated, and how much is conducted through the power lines. I supply I could just put the battery + boost converter in a tin with just the power wires coming out, and see what that does. It's a dirty approach, but combined with scoping the power lines to see just how much ripple - and any "fuzziness" there is (got a DS1054z so wont' see the HF stuff). I suspect the layout of the protoype modules I've built are less than ideal - two of which are on single sided boards, albeit with a single sided 0.8mm copper clad board glued to the back and stitched to ground. Reading up on large current loops between the input cap, L and switch shows that some of my layouts aren't great.Quote from: T3sl4co1l on September 04, 2024, 08:54:57 pmThats a lot to unpack, but my idea was indeed a "3 terminal device", albeit with extra connections for enable and a pin to select between two different output voltages (resistor to FB, to be grounded by host). That should mean any IO filtering easier since, as you said, they share the same ground input/ouput, so the filtering components can sit right at those pins.I know a shield is perhaps overkill, but given I was going to knock up some small converter modules anyway - adding the provision for a shielding can doesn't add to the cost of the PCB, and given the small size (~15 x 21mm?) the ones I've found aren't that expensive.So it looks like I've got a few tests to perform to have some idea of how much is supply ripple, and how much radiated.. then the source of this noise, it's frequency compenents etc.. It's a lot of effort, and compounded by the fact I tend to use several different converters from several different manufacturers. But perhaps I can pick just two for now.I was surprised they don't exist as a product, but given the rather narrow application (single/double cell boost, <100mA, very low noise for radio applications etc..) and the fact that it seems half decent layout and filtering *should* be enough, I guess it just isn't worth manufacturering at a price point that would be practical.At the risk of derailing the thread - anyone have any preferred boost convertes for such applications? We're talking low voltage input (1-3V), synchronous <100mA out. I have quite a few MCP1640B's that work well, but really don't like anything over 50mA (@5V) from two cell input, and a few TPS61023. But there are loads to choose from - too many to test.

author: radiolistener
author_rank: Super Contributor
timestamp: September 06, 2024, 04:47:45 am
content: Quote from: Buriedcode on September 04, 2024, 02:59:59 pmYes, it is crucial to use RF shielding around the DC/DC converter. The shielding helps minimize electromagnetic interference (EMI), which can affect other electronic components (such as RF receivers or sensitive ADC or PLL circuits). Also very important to use proper filters on both the input and output of the converter to reduce high-frequency noise that could propagate through the power lines.Quote from: Phil1977 on September 04, 2024, 03:24:36 pmNo, this is complete false claim. Even a small, low-power boost converter can radiate significant noise in the <200 MHz range, which can interfere with RF communications. This is especially true if the converter is not designed with EMI mitigation in mind and/or uses long wires without proper filtering close to the converter and/or lacks proper shielding.The frequency band most affected by boost converters typically ranges from 20 kHz to 7 MHz. However, the impact can extend up to 150-200 MHz and beyond, as higher harmonics and switching frequencies can produce interference in these higher ranges. Boost converters can generate significant electromagnetic interference (EMI) within this broader spectrum, depending on their design and operational conditions.It is practically impossible to completely eliminate EMI from a boost converter for radio receivers. However, it is possible to shift the boost converter's noise to unused parts of the spectrum and minimize it as much as possible using various techniques, such as filters and shielding. In this way, you can minimize the effect of the boost converter noise on your radio receiver.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 06, 2024, 07:35:52 am
content: Quote from: radiolistener on September 06, 2024, 04:47:45 amI said it´s not emitting by itself, and physics strongly supports this statement. But no need to argue, we practically recommend the same thing. Filter the in- and output and -if necessary- shield the converter against near field couplings.And it´s just nonsense that SMPS will always disturb transmissions. It´s only a question of how much engineering and components you invest into the filters. That´s why for many setups it´s just more reasonable to use linear converters, but with free choice of filter technologies and a solid metal backplane you can suppress all frequencies below the noise level of the most sensible receiver.Edit: If you don't believe it, look at6min30s clearly shows a more or less standard SMPS in a Rohde & Schwarz spectrum analyzer going from 5kHz to 3Ghz. And please don't tell me R&S is doing it wrong...

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 07, 2024, 04:39:15 am
content: Quote from: Buriedcode on September 04, 2024, 02:59:59 pmUse LiFePO4 and you won't need a regulator to run 3.3V logic from it. The operating voltage range of a single cell just happens to be within what most 3.3V logic is specified to operate from.

author: radiolistener
author_rank: Super Contributor
timestamp: September 08, 2024, 09:43:47 pm
content: Quote from: Phil1977 on September 06, 2024, 07:35:52 amNo, this claim just demonstrates a lack of understanding of physics and practical RF experience. Even a battery-powered DC/DC converter with no external wires and galvanically isolated from any external connections still emits EMI noise. While this noise may be minimal and difficult to detect on a spectrum analyzer with a wide bandwidth span and a high noise floor, it can be easily picked up by a narrowband radio receiver, such as an AM broadcast receiver operating in the LW, MW, or SW bands. The fact that even isolated circuits can generate detectable EMI highlights the importance of proper design and shielding to mitigate these effects.Quote from: Phil1977 on September 06, 2024, 07:35:52 amThe real nonsense is the belief that you can build a circuit that will never disturb a radio receiver. This is physically impossible. Even with an excellent design, including high-quality DC/DC converters, expensive filtering, and near-perfect shielding, EMI emissions can still be detected by a radio receiver with a narrower bandwidth and lower phase noise of it's local oscillator (LO). Furthermore, as technology advances, radio receivers become more sensitive and capable of detecting even lower levels of interference. This underscores the fact that while good engineering can significantly reduce EMI, it cannot entirely eliminate it.While it may be possible (but very expensive) to design a DC/DC converter with good filters and shielding that minimally interferes with a broadcast radio receiver with audio output, creating such a buck converter for powering lasers used in laser spectroscopy is a very non trivial task. This is because it is much more sensitive to the noise. The strict ultra low noise requirements in such applications often necessitate the use of linear power supplies.Quote from: Phil1977 on September 06, 2024, 07:35:52 amYour claim demonstrates a fundamental misunderstanding of physics and RF theory. Using a 3 GHz bandwidth results in such a high noise floor that you won't even detect the presence of relatively strong carriers from distant transmitters, even though these carriers would be clearly received by a radio receiver with a sufficiently high SNR.Attempting to identify weak noise sources with such a wide 3 GHz bandwidth is impractical and scientifically unsound, which is why your example is flawed and frankly, laughable.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 08, 2024, 10:01:33 pm
content: QuoteNot read all your content (sorry, but you ramble a _lot_ and lots is often erroneous. I'm not trying to be rude, but it has to be said). That's not how a spectrum analyzer works. Take a look at the architecture of one, and compare and contrast with a radio receiver.

author: radiolistener
author_rank: Super Contributor
timestamp: September 08, 2024, 10:17:29 pm
content: Quote from: shabaz on September 08, 2024, 10:01:33 pmSorry, but if you believe that weak noise can be observed over a 3 GHz span, you are mistaken. This reflects a lack of understanding of how spectrum analyzers and radio receivers work, particularly how their bandwidth/span is directly linked to the noise floor. I recommend taking the time to carefully read and understand the principles behind these instruments to fully grasp how they operate.Just try reading the theory carefully, without skipping sections of the text as you usually do. You’ll discover many new and interesting facts that you previously missed because you skim through and skip parts of the text.As a start point, I recommend considering why oscilloscopes with >=100 MHz bandwidth include a 20 MHz bandwidth mode and why exactly this narrow-band mode is specifically used for assessing power supplies noise. Then read carefully what is SNR, what is RBW, what is VBW, etc. And how selected bandwidth affects SNR.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 08, 2024, 10:40:33 pm
content: Quote from: radiolistener on September 08, 2024, 09:43:47 pmAt what distance?QuoteCurious, would you stake any money on that claim?Serious; right here, right now. We can get a neutral 3rd party to escrow the money, and a small group together to judge the award. That way there's no "well but I meant--" chicanery from either side, accept the result, done and done. Waive right to lawsuit or arbitration, easy enough to handle the rules, in confidence, in public view here, make a little spectacle out of it, good times had by all, eh?How much would you put on it? $10? $100?$1000? Might as well make it worth my time to build something, right?The proposal would be something like... I build a module, and you have to detect near field or radiated emissions from it. The module does something clearly nontrivial, like light a white LED from a AA cell, or output 5V from 12V with >40% efficiency. Maybe the LED would be enclosed, maybe the cell as well; maybe input and output would both be wired to maximize chances of success. Open to options. Maybe near field would be too much of a "gimmie", and beyond the spirit of the above claims -- but just as well, I might allow any chance to succeed, short of tearing the thing apart. Further stipulations might be that it has to use an inductive SMPS converter stage, perhaps Fsw(avg) above some minimum, so it's not simply a charge pump, or a dumb iron-core inverter, but reasonably representative of commercial practice, just cleaned up particularly well.Alternately, a more usefully-didactic rendering -- maybe money doesn't get involved at all, rather the value is a case study for both participants and readers -- how about something like: you make a converter, as best as you can, but which you are still reading signal from. Send it to me, and I'll fix it until you can't. Then you figure out some other method maybe, to observe emissions from it. Back and forth, so it goes.I feel pretty confident in proposing and accepting such a bet; how about you?QuoteAh, but you forget. It works the other way, too. How pray tell do you pick out e.g. a spread spectrum signal from below the noise floor? If you don't know what the precise clock or message (spreading) signal is, if you don't have any coherent reference, how can you detect it?People complain about spread spectrum being some kind of devil's bargain but it works for good reason.Put another way: suppose you had access to the internal clock signal. You could wire that to a lock-in amplifier, and pick up emissions practically across the world. But how do you do that without the phase reference? How do you do that incoherently?It sounds like you have a method, which you should patent quickly, because you can make a hell of a lot more money on it than some stupid bet on the internet will.Tim

author: radiolistener
author_rank: Super Contributor
timestamp: September 08, 2024, 11:04:27 pm
content: Quote from: T3sl4co1l on September 08, 2024, 10:40:33 pmabout 6000 km

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 08, 2024, 11:10:18 pm
content: I'm keying my flashlight to Morse code right now, what am I saying?Tim

author: radiolistener
author_rank: Super Contributor
timestamp: September 08, 2024, 11:55:53 pm
content: Quote from: T3sl4co1l on September 08, 2024, 10:40:33 pmUnfortunately I will not be able to get your money due to limitations in my country.But I can help you detect the noise from your circuit, and you can find it yourself. The issue is not whether it is possible (because it is possible) but rather how narrow the bandwidth will need to be. If your circuit is relatively low noise, you might need a radio receiver with an ultra-low noise LO, LNA with low NF at frequency of interest, and a sensitive ADC with DSP for processing. This could be expensive if you don't have a good SDR radio. However, we can try using your oscilloscope if it allows capturing long samples and processing them in MATLAB/Octave. I can assist you with the processing if you want to conduct that experiment."Quote from: T3sl4co1l on September 08, 2024, 10:40:33 pmYou don't need to know the exact frequency to detect EMI from a DC/DC converter because it doesn't have a very stable carrier and has phase noise that creates a broader spectral hump around the main peak. All you need to do is detect the increase in the noise floor.If you understand the math, you know that this can be achieved through simple averaging. Yes, it may take longer time to detect quieter noise due to the Shannon-Hartley theorem: C = B*log2(1+S/N).Thus, a narrower bandwidth results in slower detection of the signal presence. But on the other hand, you are almost unlimited in your ability to narrow the bandwidth to detect a signal that is as weak as you need.As you can see, there is no magic involved - just math.Quote from: T3sl4co1l on September 08, 2024, 10:40:33 pmAs I mentioned before, a better way is to shift the noise into an unused part of the spectrum. This technique is used in SMPS power supplies for radios, which include a control knob to adjust the frequency and shift the noise away from critical frequencies.Quote from: T3sl4co1l on September 08, 2024, 10:40:33 pmIt looks obvious that you understand that it is possible, because you trying to limit the use of coherent LO. Isn't it?But how to build precise frequency standard is another story... We're talking here about the noise.Quote from: T3sl4co1l on September 08, 2024, 10:40:33 pmYes, it’s possible, but it requires using a very precise and stable frequency standard, and the information transfer speed will be very low, which does not offer advantages over a classic high-power transmitter with an antenna.This is how ELF transmitters work to send command orders to underwater submarines that carry nuclear weapons. These submarines may be at depths of 1 km or more, where conventional communications do not work. ELF transmitters use a 76 Hz (USA) or 82 Hz (Russian) carrier to transmit data, but the data transfer speed is low due to the narrow bandwidth (see Shannon-Hartley theorem). The message transfer speed is low, but it's enough to send a short encrypted message with an order to do nuclear strike or other command.Quote from: T3sl4co1l on September 08, 2024, 11:10:18 pmFirst, I don't have the equipment to detect signals with such a low level. Second, I'm sure you're sending it too quickly, so it will be hard to distinguish from environmental noise. However, it's clear that by doing it you increase the environment noise level. Isn't it?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 09, 2024, 12:44:36 am
content: Quote from: radiolistener on September 08, 2024, 11:55:53 pmHah, fair enough. Under the circumstances, perhaps a donation would be in order? $1000 to the charity, relief fund, etc. of your choosing?QuoteSure, that works when the signal is coherent, just average the fuck out of the noise and out comes the signal. But something is missing between precisely these two paragraphs:You can't average that which is already noisy.Both drop at precisely the same rate.If I have a signal that averages as C = B*log2(1+S/N), added to a linear channel with noise that averages as C = B*log2(1+S/N), what margin of likelihood, or channel capacity per bit error rate, can you get through there?Put another way: what confidence interval can you put on your receiver picking up -98.2736dB of atmospheric noise, versus -98.2661dB of atmospheric noise plus some potential source? Can you identify the source -- if not unambiguously, then within some margin of likelihood?At what point does the statistical variation of the background itself, so utterly overwhelm the source of interest, that it is indistinguishable under any and all possible analyses?Quote--It's not.Two things:1. You're completely missing the opposite side of the equation. (I cannot ascertain whether this is accidental or intentional, but neither one is a good look?)If *either of* the transmitter carrier, or the receiver LO, is noisy, the received signal is noisy -- potentially, lost in the noise floor.Critically: the result isidentical and indistinguishablewhether we introduce phase noise, frequency modulation, or other spreading, into the transmitter's timing source,or the receiver's timing source.Indeed we could have a referenced (perfectly coherent) system, where both transmitter and receiver are clocked from the same reference (pure or otherwise; it doesn't matter at this point), and over-the-air reception is good down to whatever averaging level works; that's a lock-in amplifier. But suppose we add a PLL, modulated with incoherent FM or PM, inlineto eithertransmitter or receiver: the whole thing crumbles apart, no matter how long the averaging is. (Actually, maybe it still works for PM, if the phase error is less than 180°; it just takes longer to average out. An undefined (i.e. evenly distributed) phase error however, isn't going to see anything. Likewise, an FM error, as a fixed frequency shift for example, completely eliminates what was otherwise a DC/baseband signal. Maybe you know to retune the receiver, or pick out the tone in the audio output; but how do you know that's really the one anymore, or just some interfering signal?)It is necessary and sufficient that *both* transmitter and receiver be pure, to whatever coding scheme the system uses (doesn't have to be single-tone, can be chirped, can be spread, whatever), in order to achieve communication between them.Or, say in optical terms: suppose we have a two-arm interferometer. If we add a random phase plate (say an electrically modulated one, white noise spectrum up to the frequency limit of the detector),to either arm, or both,the interference pattern is GONE, bupkis, nada. Only when the signal and reference are coherent, do we detect a pattern -- receive a signal.2. ELF transmitters work with very stable transmit frequencies, and very stable receiver tuning. Both combined, means relative coherency is maintained, and a stable signal can be received, even if the signal levels are very low indeed. (On top of which, the bitrate is quite low, but not by an extreme degree compared to the already extremely low carrier frequency.) So it's an example which seems to prove my point and defeat yours?QuoteOh so you don't anyway... you're just blowing steam.I mean, I guessed as much, two replies ago -- but you could've saved us all some effort (and yourself a lot of embarrassment*) by just saying so in the first place -- or not saying anything at all.Look -- I don't know at what point you can still learn from this. I've chosen to lean against this post more strongly than I might otherwise, and so don't expect much acknowledgement in return. I still welcome a healthy and receptive conversation here. But proclaiming half or un-truths as fact, without knowing your own gaps of knowledge about it? Or worse still, if you are in fact aware of your own ignorance, or misrepresentation, and still choose to post it as fact? Either way, that's not something I will allow to pass unchallenged.Tim*Or myself for taking the bait.

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2024, 02:53:34 am
content: Quote from: T3sl4co1l on September 09, 2024, 12:44:36 amI didn't said that the DC/DC converter is a transmitter here. The DC/DC converter is not a transmitter, but an EMI source. Both the transmitter and receiver can use an ultra-low phase noise LO with a stable enough frequency to send the message. I assume that the LOs of the transmitter and receiver are synchronized with sufficient accuracy to consider them coherent.However, the DC/DC converter placed on the path will add some noise, which will reduce the SNR and make signal reception worse. This noise can be very small, may be so small that even not detectable with all existing hardware, but it still add noise. This is what I'm talking about.And this is exactly what happens in topic-starter case. He don't use DC/DC as transmitter. It just works as EMI source which reduce SNR for communication channel between transmitter and receiver.Quote from: T3sl4co1l on September 09, 2024, 12:44:36 amThis is an unfair manipulation on your part.It’s like claiming that since you don't have the equipment to test if radio communication is possible at a distance of more than 100,000 km, it proves that electromagnetic waves cannot travel more than 100,000 km...No, the lack of sufficiently sensitive equipment doesn't prove anything. If I don't have the equipment to detect the presence of a very small noise source, it doesn't mean that there is no noise at all from your keyed light.PS: regarding to the bet I sent you private message

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2024, 03:35:58 am
content: Quote from: T3sl4co1l on September 09, 2024, 12:44:36 amNo, it proves my point and refutes yours. The message can be received because its bandwidth is narrow enough to achieve a sufficient SNR to decode the message. If you introduce an EMI source with enough noise to degrade the SNR, it will be impossible to decode the message.You can make the message bandwidth as narrow as you wish, reducing the noise power as much as needed, but this also requires a more precisely synchronized LO for both the transmitter and receiver. Therefore, your ability to listen for very weak signals is limited by the stability of your frequency standard.And if you display the spectrum with a narrow enough bandwidth span on your receiver, you will see EMI noise from a nearby DC/DC converter, even if it has good shielding and very good filters.To stop that discussion I can say from my experience thatany kind of DC/DCconverter, with any kind of shielding and filtering, produces high enough noise peaks (at least 20-30 dB above noise floor) to be visible on the spectrum waterfall of a medium-quality receiver. And there is no need to use very expensive ultra-low phase noise oscillator for LO to detect DC/DC module noise.The best result you can get with a 2 MHz DC/DC synchronized to the receiver LO is that it has fewer spurs, but its noise is still very visible. However, its noise is cleaner and more narrowband which is good for receiver.I never seen DC/DC which don't have visible noise on the receiver spectrum waterfall. But even if you build it using modern cutting-edge technology, I’m sure it will still be easy to see its noise on a receiver. It might require a slightly less noisy LO, but I think it would still be visible even with a typical Chinese oscillator.I can say this with confidence because I have tested DC/DC converters in practice and have seen their noise with my own eyes on the spectrum waterfall. I also know other people who have designed receivers using expensive DC/DC modules and extensive filtering measures, he has the same results. This is why I'm saying that it's practically impossible to have DC/DC which don't have visible noise on receiver.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 09, 2024, 05:48:50 am
content: Quote from: radiolistener on September 09, 2024, 03:35:58 amThe power supply of my homebrew GPSDO has a DC-DC converter to maintain constant heater voltage for the OCXO as my battery voltage drains over the course of several hours of field portable operations.I can see NO increase in the waterfall, and definitely not 20-30dB! This is field operations away from urban electrical noise.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 09, 2024, 05:58:35 am
content: Quote from: radiolistener on September 08, 2024, 09:43:47 pmPlease read and understand some good introduction into spectrum analyzers. 3GHz is the total bandwidth of the device. You set the bandwidth for each scanned point with the RBW, which goes down to 1Hz at the shown model. The noise floor of the spectrum analyzer is specified to -165dbm typical - how does that compare with a decent receiver?Radiolistener goes to my personal ignore list - he talks of personal experiences while other people talk about science.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 09, 2024, 06:02:23 am
content: There's so much inaccurate information from radiolistener, I ignore it mostly. Sorry if that appears rude, but I'm not trying to be. I don't like saying it, but I feel I have to.Here's a discrete DIY supply, measured before and after adding a cheap LDO IC (performance would have been even better with a more modern LDO with better PSRR). I'm no power supply engineer. I just took some effort to reduce harmonics and it could still be improved further. LDO (TLV740P) is not visible in the photo, because it's soldered on the underside.By 1 MHz, it is already down to -140 dbV. That noise visible past that (around 50 MHz) is other equipment, not related to the supply (i.e., that noise is still present even when the supply is switched off).This power supply would have no noticeable impact on a radio receiver at VHF. Nor HF.

author: jonpaul
author_rank: Super Contributor
timestamp: September 09, 2024, 06:13:19 am
content: Wrong converter topology.use soft switching converters, resonant etc, set sw freq below band of interest.j

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 09, 2024, 07:38:44 am
content: Quote from: radiolistener on September 09, 2024, 02:53:34 amAh OK, you're still thinking of the OP situation, possible effects etc.This conflicts with the usual understood meaning of "EMI source": what is a source but a[n unintentional] transmitter? (Standards in English use this phrasing.)Then, in terms of the lock-in example, you suppose that, more or less to say: powering one or the other unit with an SMPS,willintroducedetectableaberration in link quality -- serving the role of the introduced PM/FM noise. Would that be a reasonable statement of things?Quote from: radiolistener on September 09, 2024, 03:35:58 amOk, this is much improved -- stating itas factstands to mislead readers -- but stating it asopinion and experienceleaves open the possibility that you just haven't seen every example, etc. I apologize for the tone I took before.Tim

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2024, 12:23:10 pm
content: Quote from: T3sl4co1l on September 09, 2024, 07:38:44 amWhat I wanted to say is that powering a receiver from an SMPS leads to some noise, which will be visible on the receiver. This doesn't mean it will break the link, because if the SNR is sufficient to maintain the link, you might not notice the noise. So, it depends on many factors—the signal level, the noise level within the receiver's bandwidth, etc. It may turn out that the main noise power of the SMPS is outside the receiver's bandwidth, and in this case, the degradation in link quality will not be noticeable within the receiver's dynamic range. In other cases, the noise power from the SMPS may overlap the receiver's bandwidth and significantly affect the link quality, but this still doesn't mean it will break the link. If the remote station's signal has enough SNR, the link will work, but the distance over which you can receive it will be affected.However, if you don't notice the influence of the SMPS on the receiver at a certain frequency, it doesn't mean that it doesn't exist at other frequencies. That's what I meant when I said that any SMPS produces noise that can be detected by the receiver.Quote from: Phil1977 on September 09, 2024, 05:58:35 amI'm glad to see that now you understand the relationship between the selected bandwidth and the noise floor. This is great progress. Previously, you tried to find noise from an SMPS with a frequency span set from 5 kHz to 3 GHz.Now, connect the output of your SMPS to the spectrum analyzer input through a DC block and try to check its noise with a 10 Hz span setting around the conversion frequency of your SMPS. Do you still not see the noise?Quote from: Phil1977 on September 09, 2024, 05:58:35 amWhat you still missing here is that sensitivity is linked with bandwidth and it's a big mistake to talk about sensitivity specified for 1 Hz bandwidth when you looking at 3 GHz bandwidth. Are you sure that the -165 dBm sensitivity is specified for a 3 GHz bandwidth? Or is it for 1 Hz? There's a huge difference.For receivers typical bandwidth to talk about sensitivity is 500 Hz which is used for CW mode.What is your spectrum analyzer MDS sensitivity at 500 Hz bandwidth?Quote from: shabaz on September 09, 2024, 06:02:23 amAre you kidding? Your oscilloscope clearly shows SMPS noise from -40 dBV on VLF band to -115 dBV on SW band and -105 dBV on VHF band. -105 dBV is about -92 dBm power for 50 Ω. This is high enough to flood the weak signal with noise and make DX link impossible.For example, the peak power of DX VHF station can have power level about -120 dBm or even less.Typical MDS sensitivity of VHF receiver for 500 Hz bandwidth (CW mode) is about -140..-150 dBm, this is about -163 dBV.And you talking that -40 dBV noise would have no noticeable impact on a radio receiver? Seriously?A VHF receiver that shows -105 dBV (-92 dBm) of noise from its own SMPS is just a piece of junk.

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2024, 02:18:44 pm
content: Quote from: T3sl4co1l on September 09, 2024, 07:38:44 amWell, do you have a practical example of such SMPS whose noise is not detectable with a receiver that has an MDS sensitivity of -145 dBm @ 500 Hz? (about 0.012 µVrms @ 500 Hz)To be clear, I do not exclude the possibility that such SMPS with so low noise can be created with modern cutting-edge technology, but I do not believe that they exist and are practically used.And if you try to implement a DC/DC converter with noise below at least -120 dBm, I'm sure you'll end up using a linear regulator instead of an SMPS. Even if you add a good enough filter, you will still need to deal with leakage issues, such as magnetic coupling with inductor. That's the reality.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 09, 2024, 02:39:24 pm
content: Quote from: radiolistener on September 09, 2024, 02:18:44 pmWhat do you define as "cutting edge" technology?What do you define as "old traditional" technology?Modern power supplies have moved away from hard-switched PWM, towards soft-switching ZVS & LLC techniques. This movement has been happening for many years now, over 20 years. Much "old traditional" technology are probably in e-waste by now.

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2024, 02:58:17 pm
content: Quote from: Andy Chee on September 09, 2024, 02:39:24 pmWith modern technology, you can use various ready-to-use low-noise solutions integrated into chips. Additionally, electromagnetic simulation tools are available to optimize PCB wiring and component layouts to reduce noise leakage.In contrast, with older technology, such tools and ready-to-use components were not available, requiring significantly more time and money for the development process.For example, using an oldST1S10chip with good filters result in noticeable noise on the receiver. However, I don't exclude the possibility that with more modern chips, you might achieve better results. I also don't exclude the possibility that electromagnetic modeling of PCB layout could help to significantly reduce the level of noise leakage.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 09, 2024, 04:50:57 pm
content: Quote from: radiolistener on September 09, 2024, 02:18:44 pmWell sure, we already have one in the thread: forhttps://www.eevblog.com/forum/projects/shielding-boost-converter-for-rf-transceiver/?action=dlattach;attach=2365825;imageabove 500kHz, harmonics are dropping about as -80dB/dec(!), so probably by about 3MHz, it's below there. We can'tconfirmthat from the data given, but it seems likely to be true. (The peaks at 50 and 100MHz may be aberrations of acquisition, or interference in the setup -- commercial stations, perhaps, but they might also be faint oscillation, for which ferrite beads might suffice. We'd need a metal box, LISN, coaxial connections, and probably LNA, to have a better idea. The scope might also not have good dynamic range in those frequencies.)If a transceiver is insensitive to these lower frequencies but not the higher ones, then that's that, there you have it.If you contend thatthere exists a receiverthat's sensitive to any frequencies... well yeah I gotta say there are some pretty shit designs out there, that doesn't mean they should be used.But even if so, these lower frequencies are easy to filter; it's hard to make a simple (as calculated) lowpass filter with more than, say, 2 or 3 decades of asymptotic performance, but evidently this supply only needs two decades worth of filtering; we might put in a two or three staged filter anyway (i.e., cutoffs of say 1kHz, 1MHz, 100MHz), just to be sure it's clean beyond that.A capacitor multiplier might also be used, with or instead of an LDO. -100dB at 20kHz isn't a compact filter but it's also not wild, and a staged approach can achieve that easily.Things are more difficult if such a clean isolation barrier is required, but that too can be mitigated mostly by stuffing either side of the isolation barrier inside a metal box to block its common mode voltage; the CM path might still emit, but what's inside the box(es) doesn't see it.So too, if the transceiver is sensitive to ambient fields, not just conducted (supply) noise. Stuff them both in boxes and no one's the wiser.QuoteCurious, why "cutting edge"?Is a 50/60Hz thyristor supply not "SMPS"? Is an iron-cored inverter (audio frequency, or maybe just above to avoid whine, as the above example) not an "SMPS"?Is a low-harmonic class-C oscillator/amplifier, plus resonant tank and rectifier, not an "SMPS"? (It might not be as efficient as a switcher proper, but it's definitely more efficient than an equivalent transformerless linear supply for a high enough dropping ratio -- 70% efficiency should be feasible.)Is a magnetron + rectenna not an "SMPS"?...okay, that's kind of out there, one would almost certainly not have to go to such lengths. But it leaves open a further possibility: why not crank "Fsw" up even further, use LEDs + solar panels? Total efficiency isn't going to be great (20% if you're lucky?), but that's still better than a linear supply of high enough dropping ratio.Is an SMPS with linear postreg not an "SMPS"?In short, we can put the tones and spurs wherever we want, and there exists a filtering strategy to deal with any of them -- given enough space or budget. The mains pulses of the thyristor rectifier, or say a saturable reactor-controlled rectifier, can be filtered with enough iron and copper, even if we don't allow a minor voltage drop for a linear postreg; the carrier and harmonics of a traditional hard-switched buck, or switching transients of the thyristor, can be filtered with iron or ferrite; and the upper harmonics of fast switchers or VHF+ oscillators can be filtered with ferrite or air-core inductors, or transmission line structures, absorbed in resistive materials, and blocked with shielding.If what you were saying were completely true, that absolutely positively nothing can hide -- SIGINT would love to hear about it; however, there are such things as signals-approved equipment (various internal signals, adequate filtering and shielding to prevent their leakage), and even filters (mains filtering from some kHz up). Granted, those filters will have some standard minimum attenuation, not necessarily 150dB or more at any frequency, but as part of a system, easily more than 150dB from privileged sources to potential exterior points can be achieved.Tim

author: shabaz
author_rank: Frequent Contributor
timestamp: September 09, 2024, 06:42:28 pm
content: Quote from: radiolistener on September 09, 2024, 12:23:10 pmSince you're such a polite guy, I've attached some traces. I'm sure it won't convince you.For anyone else; I'm no power supply- (or power supply measuring-) expert, I used a 10 nF capacitor for DC removal (should be fine for measurements beyond a few hundred kHz).The traces are for 2 MHz chunks, randomly chosen to be 10k-2MHz, 3-5MHz, and 10-12MHz.By the time I got to the 10-12MHz chunk, the double-shielded coax was insufficient, I was seeing noise from outside, at about 11.9 MHz, so I swapped over to semi-rigid coax at that point. Also needed to drop to 10 Hz RBW by then (the other traces are at 30 Hz RBW), to get the noise floor lower.I've got max-hold applied, but I only waited for about three sweeps or so to reduce the time spent on the exercise.

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2024, 10:53:35 pm
content: Quote from: shabaz on September 09, 2024, 06:42:28 pmJust try pairing your DC/DC converter with the receiver and see if its input isn't flooded with noise above the receiver's noise floor, which is around -145 dBm. Then you can return to your measurement setup and test what's wrong with it.For better results, place inductor of your DC/DC close to receiver input filters inductors and make sure that receiver preamp is powered from it...At a glance, I suspect you just selected a frequency with minimal noise and didn't show the frequencies with the actual peak DC/DC noise. Previously, you showed a picture with -90 dBm noise peak at around 50 MHz. Could you please find the exact frequency of this peak and show us the noise details at that frequency?Also, yourprevious pictureshows-26 dBm(crazy noise!) noise peak at 11 kHz,-30 dBmat 50 kHz, and many other spurs below 1 MHz. Where did those noise peaks go in your last measurement? Did you manage to eliminate them? Could you please show us detailed picture of these noise peaks?Such noise below 1 MHz is very-very critical for receivers, because every received frequency is shifted down to exactly this frequency band.I just wonder why you hide the frequencies with the maximum noise peak and instead decided to show a frequency where the noise is minimal? Did you do this deliberately, or was it a mistake?Overall, based on your initial measurements, your DC/DC converter isextremely noisy, like a steam engine, and is entirely incompatible with receivers. Anoise level of -26 dBm at 11 kHz is a very poor result, and it's the primary issue if you're considering compatibility with receivers. This frequency will propagate through the mixer, leading to noise spurs every 11 kHz step on the receiver. This is why I wrote "Are you kidding?" when you show these results and talked that your DC/DC is not noisy...

author: shabaz
author_rank: Frequent Contributor
timestamp: September 10, 2024, 12:33:10 am
content: Quote from: radiolistener on September 09, 2024, 10:53:35 pmThis is clutching at straws. Pretty much every architecture will include amplification and signal processing (analog and/or digital)beforedown-conversion. And you say this is all very poor, but let's put it in perspective. It's 160 uV RMS, according to the automated measurement on the 'scope. Seems pretty good considering I used such a cheap LDO on the output.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 10, 2024, 12:37:47 am
content: And here's the measurement at 50 MHz as requested. With max-hold turned off since you don't like that.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 12:50:45 am
content: Quote from: shabaz on September 10, 2024, 12:33:10 amThe main issue with low-frequency noise for the receiver is that it propagates through the mixer, resulting in noise spurs at every 11 kHz interval. Consequently, a cluster of extremely high spurs below 1 MHz on your DC/DC converter becomes a significant problem for the receiver. This leads to numerous additional noise frequencies, potentially covering the entire IF bandwidth.For a receiver, it's better to have higher amplitude noise at 1 MHz than lower amplitude noise at 10 kHz. This is because a 1 MHz spur interval is preferable instead to polluting the entire bandwidth with spurs every 10 kHz.Also note that it is very difficult (almost impossible) to shield a receiver from low-frequency near-field coupling with your DC/DC converter at short distances, especially from the magnetic pulses generated by the DC/DC inductor. It's very hard to shield magnetic field at near field region.I have a device that uses a DC/DC module, and due to its small size, it is placed about 40 mm away from the LPF inductors. This arrangement leads to significant noise interference. A field probe detected very high field strength around the DC/DC module. I tried various methods to shield it and even changed the orientation of the inductors, but without success. The only viable solution was to replace the DC/DC module with a linear regulator.Quote from: shabaz on September 10, 2024, 12:33:10 amJust compare your 160 uV noise with 0.012 uV amplitude of processed signal...Your noise amplitude is 13000 times higher than the signal!And you say that this is pretty good?

author: shabaz
author_rank: Frequent Contributor
timestamp: September 10, 2024, 01:21:09 am
content: Yes, it is low noise; manylinearsupply power bricks for radio receivers will have higher noise or ripple. Some linear supplies will have noise at MHz frequencies. I'm presuming you're not now into audiofool territory.For the portions of circuitry that needs lower noise, it's a solved problem to reduce noise below 1 MHz; I deliberately chose a low-cost LDO.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 02:05:16 am
content: Quote from: shabaz on September 10, 2024, 01:21:09 amYes, and this is why it's almost impossible to listen radio below 7 MHz in modern cities. The reason - a lot of SMPS power bricks around...We have power outage here and when it happens the noise floor drops down to 60-80 dB and I can listen very weak DX transmitters at 0.5-7 MHz frequency with no issue. But when power is enabled again, the noise floor rise up and it's impossible to listen even strong stations...Quote from: shabaz on September 10, 2024, 01:21:09 amThat's not a problem if it uses proper shielding and filters. MHz band noise is more easy to filter and to make shielding. And it has less effect on the mixers and less spurs pollution on IF bandwidth, so it's preferable for receivers. But once its noise is emitted on the air it also will be an issue.Quote from: shabaz on September 10, 2024, 01:21:09 amNo. For radio receivers, it is common situation to listen -130 dBm signal in the presence of a +20 dBm signal from a nearby transmitter on a different frequency. Therefore, having a good dynamic range is essential for an effective receiver. You can easily see the difference between low dynamic range and high dynamic range receiver. And this is the difference with audio, where it's hard to detect difference between 80 dB and 140 dB dynamic range.Quote from: shabaz on September 10, 2024, 01:21:09 amLow cost usually means worse results. You get what you pay for.I recommend to try ST1S10, just to compare results.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 10, 2024, 04:12:28 am
content: You do ramble. Almost none of what you've written is relevant.You may have observed issues with the SMPS's you've used, I get that. Those manufacturers might not have cared, or had the requirements that you had or think you have.On the one hand you state that the noise is a big problem, and then when I point out you'd have the same issue with many linear supplies you state that can be filtered out.Then you go off on a completely irrelevant tangent about overloading, which has nothing to do with the issue the OP observed. He's not in a military environment (as far as I can tell), it doesn't apply at all. Perhaps I'm heavily mistaken, but he's using some typical sub-GHz modules and ICs not really intended for a battlefield.Then you tell me low-cost usually means worse results. Very insightful. I selected that LDO because that's what I want to use.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 04:47:18 am
content: Quote from: shabaz on September 10, 2024, 04:12:28 amThe same problem with linear PSU?Could you please explain, what you're talking about?This is something new... I've never heard about noise issues from linear PSU for receivers...To be clear, I was talking about switching mode PSU running at 1 MHz... Yes, they are more friendly for receivers, especially when you put their noise to unused frequency band.Quote from: shabaz on September 10, 2024, 04:12:28 amIt's not about overloading, but about sensitivity. Sometimes the impact of SMPS noise is much worse due to the low dynamic range of the receiver. This occurs when SMPS noise is so strong that the receiver's dynamic range isn't sufficient to maintain high sensitivity. To avoid overload, the receiver reduces its gain, which in turn reduces sensitivity. This is a common issue in inexpensive Chinese radios like Baofeng and Quansheng.Overall, all SMPS units can cause interference with radio receivers and sensitive equipment. Sometimes SMPS EMI can affect even digital circuits, for example see inductor orientation issue for RP2350 boards. Therefore, it's preferable to use linear regulators when possible. The only downside of linear regulators is their lower efficiency.I don't like SMPS due to their interference for receivers.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2024, 05:38:06 am
content: A linear supply might be misbehaving to do this, but squegging or oscillation can indeed happen, and the PSRR at high frequencies is generally poor (better for emitter follower than open-drain LDOs, but there are high performance kinds of the latter too).Even a normally-behaving one isn't much quieter than shown: typical ref + error amp noise is some µV RMS (say from 10Hz up to the control bandwidth of the device), even for a "low noise" one.The device shown above, with the harmonics filtered down modestly, and maybe a little cancellation just to suppress the tones, is more or less indistinguishable from a linear supply.Tim

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 05:55:16 am
content: Quote from: T3sl4co1l on September 10, 2024, 05:38:06 amself oscillation is not normal mode for linear psu, it's fault mode.Even if some linear PSU has low PSRR it still don't produce noise, it just suppresses them poorly.If you need good PSRR you can use ultra-low noise linear regulators likeLT3045Quote from: T3sl4co1l on September 10, 2024, 05:38:06 amIf you're talking about an SMPS with hundreds of noise peaks ranging from 10 kHz to 1 MHz at a -26 dBm (14.1 mV peak) level, it's absurd to claim that it's better than a linear power supply. Using such an SMPS with a receiver will contaminate its IF stage with thousands of noise spurs at fairly high levels and approximately 11 kHz intervals. This is disastrous for a receiver.Even with a poorly designed linear PSU, you would never experience such severe noise issues.If you look more closely at the picture around 500 kHz, you'll notice numerous noise spurs. So, if a receiver uses a typical 455 kHz IF, it will suffer even more, as receivers are particularly vulnerable to noise around the IF frequency.Despite the fact that above 1 MHz the noise is suppressed to -90 dBm, below 1 MHz the noise from this SMPS is so bad that I wouldn't even use it to power an LED lamp. Just because it produces too many noise which can affect my radio. It's worse than cheap Chinese SMPS...Cheap linear regulator will have almost flat line near noise floor with some small peaks near mains frequency and its harmonics.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 10, 2024, 06:19:39 am
content: Quote from: radiolistener on September 10, 2024, 05:55:16 amYour entire post, comparisons, and conclusions are misleading and dishonest.You've deliberately chosen to present the output and values pre-clean-up.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 06:28:47 am
content: Quote from: shabaz on September 10, 2024, 06:19:39 amWhat is "misleading and dishonest"?You posted picture from spectrum analyzer which shows a bunch of high power noise spurs from 10 kHz to 1 MHz and noise spike around 50 MHz. The max noise peak is at about 11 kHz = -40 dBV, this is about 14 mV peak, which well coresponds with waveform which shows pulse amplitude about 20 mV.You will never get so bad noisy output even from cheap linear regulator.I don't want to offend you, but such a power supply is completely unsuitable for radio receivers due to high noise.And talking that its noise is better than noise from linear PSU is just ridiculous, because linear PSU don't have noise at all.Sorry, but it seems like you're joking by posting example with so noisy switching mode regulator and claiming it has lower noise than a linear one.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2024, 06:40:18 am
content: Quote from: radiolistener on September 10, 2024, 05:55:16 amHeyyyy waiwaiwait just a second, reading comprehension here. I said one thing and you're going on with something else. To put it simply:Quote from: shabaz on September 10, 2024, 06:19:39 amIf someone is proposing one example, and you're willfully taking something different as your example, that's not very honest is it, right?Like... you know you can put capacitors on the thing, right? You know what a lowpass filter does, right? And how to apply it?Tim

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 10, 2024, 06:41:13 am
content: Quote from: shabaz on September 10, 2024, 06:19:39 amUnfortunately I can only confirm this statement. The spectrum shown by radiolistener looks like he has connected his analyser to some unfiltered non-sine oscillator.Now I will ignore him again. But it´s a pitty that really informative posts like from T3SL appear in this environment. We could all be here exchanging knowledge but that doesn't work if someone just wants to be bigheaded and writes as if his impressions and experiences are of more worth than others. I can just repeat myself, in 99% of the cases where you think other people are doing nonsense you just didn't understand it by yourself. I suppose radiolistener is the 1% because he starts to insult anyone he doesn't understand.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 10, 2024, 06:42:25 am
content: Quote from: radiolistener on September 10, 2024, 06:28:47 am..And that's dishonest too. Anyone is welcome to read the detail, and will easily spot what you've done. If they are unsure, I will gladly point it out to them.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 06:49:35 am
content: Quote from: Phil1977 on September 10, 2024, 06:41:13 amI just magnified picture taken by shabaz on his spectrum analyzer for his switching mode regulator and attached that magnified picture to my post...This is not mine regulator, this is shabaz's switching mode regulator and he claiming that it has better noise than linear regulator...Here is his original post with pictures from spectrum analyzer:https://www.eevblog.com/forum/projects/shielding-boost-converter-for-rf-transceiver/msg5635649/#msg5635649And you're right it's very noisy, and this is what I'm talking about...He tried to filter it with linear regulator, but his second picture clearly shows that DC/DC noise peaks are still there, although with a smaller amplitude, but sufficient to create interference for the receiver. And noise at 50 MHz is the same as before linear regulator.And I even don't talk about noise leakage from DC/DC to receiver components through common mode currents and through near field coupling.It's very hard to eliminate noise from DC/DC and adding linear regulator on the output cannot help much, because once you create noise in circuit will be almost impossible to eliminate it. It will leak through near field coupling, it will leak through wires, through ground. You even cannot imagine all path how noise can leak from DC/DC to receiver. And this is why it's better to not create the noise than to fight with it.Quote from: Phil1977 on September 10, 2024, 06:41:13 amThis is false claim. I don't insult anyone.I respect shabaz efforts in creating and measuring his power source, he has done nice job.But sorry, this power source is not suitable for radio receivers.I just support my thesis that SMPS is evil for radio receivers. Nothing personal.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2024, 07:50:48 am
content: Quote from: radiolistener on September 10, 2024, 06:49:35 amPray tell --Suppose I take a solid 1m cube of steel, drill a hole deep down into the center of it, and place an SMPS and battery there. Springs ground the unit inside the hole, and a single wire exits the block.Suppose we power a receiver from this wire.How many paths of noise leakage exist?1. Is there a leakage path through the near field? (For what frequencies? Also, suppose the SMPS is a broadband comb generator, easy to spot tones in the output.)2. Is there a leakage path through wiring?3. Is there a leakage path through ground?4. Are there any others? You should be able to enumerate themfullyin this scenario.Now, suppose I take to the block with an, erm, particularly long-life grinding wheel, shall we say. How far can I grind down this cube, until the above list changes?If your conviction is as strong as you claim it to be -- you should have an answer ready to apply to such a scenario!Tim

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 09:09:06 am
content: Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amThere is missing information about second conductor which will be involved in near field coupling. It will depends on the distance and position against cube. But I won't attempt to calculate exact numbers. At a glance it seems to me that it will require electromagnetic near field modeling.But I think it can be estimated if you provide more details about distance between cube and conductor involved into coupling and more details about geometry inside cube, especially the distance between SMPS and metal cube inner surface. And the thickness of the cube walls.Also, in order to estimate it, we need to know metal properties - conductivity and permeability.Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amYes, but its level will depends on impedance at wire feeding point. And impedance will depends on how much the wire going outside of cube. At some length we will get classic GP antenna.Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amYou mean through metal of cube?Yes, the same as for wire.Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amThrough the hole with wire. It will works like wave guide.Through far field radiation.Technically, we can classify the leakage path into three parts:- through near field capacitive coupling- through near field inductive coupling- through far field radiationAdditionally, there is some energy loss due to heating of the metal cube. And some correction which will increase these losses due to wave reflections inside metal walls of cube (between inner and outer surfaces).Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amThe list will not be changed. But it will change leakage level and proportion between different path. Any change in cube geometry will lead to change.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2024, 10:41:57 am
content: Quote from: radiolistener on September 10, 2024, 09:09:06 amWell, I did say steel. Ok fine, AISI 1020 steel, as sand-cast. What more do you need to know?As for hole, let's say 12mm ID, and wire to make 50 ohm coax. Wire is copper, C110 alloy half-hard let's say. The copper might be held centered with a solid, foam or spider structure thingy of whatever material; if you insist, let's say it's foamed polyethylene.QuoteSay we attach the receiver at the surface of the cube. Wire does not extend beyond the cube. Is there still a leakage path?QuoteOk, that's incorrect. You require further study on this point.QuoteInner...?A reminder:QuoteThere are no reflections, the material is wholly absorptive (skin effect dominant) and fields decrease exponentially with depth into the material.Attenuation will be exceptional, even at fractional Hz. It seems further study in this direction is also warranted.By extension, as the block is solid and conductive, near electric field is zero by definition.QuoteHmm interesting. If I carve off the corners to make a maximally sized octahedron let's say, what parameters change, and by how much? Surely you have a quantitative value in mind...Tim

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 10, 2024, 11:05:47 am
content: Quote from: radiolistener on September 10, 2024, 06:49:35 amI do not assume myself to teach or change anyone in its behaviour. But in my world - call me allergic or whiny-voiced or whatever - it´s neither friendly nor professional to call others ideas or stuff crap, especially not if it´s just because it´s not highly expensive or because it´s from China. I also don't assume my experiences are more valuable than others, especially if they clearly are professionals and I am not. I would never call someone stupid because *I* don't understand what he/she is saying.I still think the example of the R&S spectrum analyser nicely shows that it is possible to efficiently filter out SMPS noise. If this thread would be about technical content and not about personal vanity we could try to figure out what R&S has engineered to suppress SMPS noise that far that it is possible to operate a highly sensitive RF detection instrument. Do they use very good filters, do they use some clever spread spectrum technique (maybe actively pushing the converter frequency away from the momentary analysed frequency ?), do they use some cascaded grounding scheme?Beside a really annoying "is it possible" discussion it would be nice to have a "how is it possible" approach.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 04:51:22 pm
content: Quote from: T3sl4co1l on September 10, 2024, 10:41:57 amI will provide you with a reference to a book about electromagnetic shield design for aerospace equipment, where you can find some straightforward formulas for estimation. It explains shield estimation with an example that is very close to your question, with just one exception - without a hole with wire.Quote from: T3sl4co1l on September 10, 2024, 10:41:57 amTechnically, you described a classic GP antenna and asked whether there will be radiation leakage from it. Yes it has radiation loss.But now you proposed to connect the ground of the remote receiver with a wire to the ground plane of the transmitter antenna and are asking if it will still be able to radiate. Yes, it will radiate. Why not?I just wonder why you decided that the wire between transmitter and receiver ground will block the transmission?Quote from: T3sl4co1l on September 10, 2024, 10:41:57 amWhat exactly incorrect and why?If you claiming that the cube surface is not involved in radiation process, then this is nonsense.The surface of the metal cube acts as a counterpoise to the antenna's radiator (the part of wire outside cube).The hole with wire works here as coax cable to deliver RF energy from oscillator inside cube to the cube surface.At the cube's surface, it feeds a GP antenna, where the radiator is the part of the wire outside the cube and the counterpoise is the cube's outer surface (ground plane).Do I understand correctly that you are claiming the GP antenna fed from the oscillator with coax cable will not radiate?Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amThis is your mistake. There is no material in the world that absorbs all energy of electromagnetic wave that penetrate into it.You can find correction for wave reflections inside metal shield plate in literature about electromagnetic shield design for aerospace equipment.A little bit later I will give you the reference on a book which explains it in details with math.Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amEven if you use some meta-material with exceptional attenuation, it still just attenuate electromagnetic wave, but not cancel it to zero.And as I remember my calculations, 0.5 meters metal plate has pretty bad attenuation for magnetic field at low frequencies even above 1 Hz.Quote from: T3sl4co1l on September 10, 2024, 07:50:48 amby definition? by whose definition?Do I understand correctly that you are claiming it's impossible to radiate an electromagnetic wave with an antenna made from conductive material?Sorry, but in this case, you are saying things that are complete nonsense.The conductor canattenuateelectromagnetic wave very high butnot cancel it to zero.Therefore, for a good shielding, it is necessary to use a sufficiently thick shield plates.The intensity of the electromagnetic wave decreases as it penetrates deeper into the conductor. However, if you understand the nature of the skin-effect, you know very well that complete cancel of the electromagnetic wave does not occur even if you increase the size of the shielding cube’s wall to enormous dimensions.The majority part of the current induced in the conductor will flow near the surface, but that doesn’t mean the electromagnetic wave won’t induce currents deeper within the conductor. It will induce currents deeper than skin-layer, but they will be much smaller than close to surface. How much depends on the frequency and conductor properties. The skin depth simply indicates the thickness of the surface layer where the majority of the current flows, butnot allof the current induced by the electromagnetic wave.If electromagnetic waves could not exist inside a conductor, then electromagnetic waves would not be able to induce currents in the conductor at all, and the concept of skin-effect depth would lose all meaning.Quote from: T3sl4co1l on September 10, 2024, 10:41:57 amIt's hard to predict the near-field configuration for a custom-shaped antenna. I don’t think there is a simple rule for that. So, if you want to know how changes in antenna shape affect its near field configuration, radiation efficiency and radiation pattern, it’s better to use an electromagnetic simulator.I think for a GP with ground plane shaped as a cube or octahedron, you can use even someNEC-modelbased simulator. It uses simplified simulation, but I think it will be well enough for your case.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 05:24:53 pm
content: Quote from: Phil1977 on September 10, 2024, 11:05:47 amI said that SMPS is bad for receivers because it produces noise. That's it. Nothing personal.Do you really think that I need to ask your permission to say something about SMPS?If you think I shouldn’t say this because it might hurt someone’s sensitive psyche, well... You could just as easily be offended by anything. Am I supposed to run after you and beg you not to be upset?And yes, I think that all SMPS are crap due to their noisy nature.Some are less flawed, and some are more flawed, but they all have noise issues.Quote from: Phil1977 on September 10, 2024, 11:05:47 amYou can filter it, and it don't require to have expensive R&S spectrum analyzer. But if you try to filter it for receiver, you will realize what I'm talking about. As I proposed before, just try to power receiver from SMPS and measure it's noise on receiver. Then try to filter and shield it. And I'm sure, after that you will realize why I'm talking that SMPS is very bad thing for receivers...

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2024, 06:55:42 pm
content: As I promised before, here is the book reference: "Electromagnetic Shielding and Corrosion Protection for Aerospace Vehicles", Jan W. Gooch, John K. Daher, Springer, 2007And this page shows electromagnetic field waves inside conductor on the pictureAnd, oh horror, this page even talks about the electric and magnetic fields amplitude inside the conductor, which "is zero by definition,", though it’s unclear whose definition it was.@T3sl4co1l, how do you think is it worth to send the mail to the authors of these books, I think it will be fair to get them know that their book "is incorrect." and they "require further study on this point."? Isn't it?(to be clear, this is sarcasm, I think their book has very good explanation for EM shielding theory and I believe this is one of the best books about the subject)

author: Buriedcode
author_rank: Super Contributor
timestamp: September 11, 2024, 04:25:18 am
content: wow, I come back to the thread and.. what has happened? I'll try to read every reply because I'm sure theres some good stuff there but geez...I'm sure you all realise I wasn't suggesting SMPScan'tbe used with an RF reciever, in the same enclosure, just that my limited experience - and perhaps my less-than-optimal layout - has given my cause for concern when mixing the two on the same board (or in the same enclosure).I'm not sure I agree with radiolisteners assertion that it is almost always bad for the reciever ?

author: shabaz
author_rank: Frequent Contributor
timestamp: September 11, 2024, 05:55:26 am
content: You're just in time. Radiolistener is going to provide a practical demonstration of the shielding ineffectiveness, by sitting with his wifi-enabled laptop inside a metal cube, and sending an e-mail to some book authors. He'll send a message when he wants to be let out.He's going to start with a 1 mm thick cube, shouldn't be a problem judging by that diagram he posted showing lots of outward arrows and no numbers.