Cheap SDR devices vs classical communications receivers - Page 1
Forum section: electronics / rf-microwave

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 07, 2023, 05:12:37 pm
content: I always feel uncomfortable when I encounter somebody breathlessly extolling the virtues of a cheap DVB receiver used as a software defined radio, or for that matter something like a "Malachite" receiver.The problem, as I see it, is that this sort of thing has little, if any, tuned RF amplifier as a frontend: even allowing for the advances in component design over the last couple of decades I can't help but feel that even as a get-the-job-done hack it leaves a lot to be desired.Would there be any advantage to wiring something like a Realtek RTL2832U into a classical communications receiver after the IF stage, in order to get both a well-designed RF frontend and the rich environment provided by e.g. GNU Radio?MarkMLlhttps://www.nominet.uk/using-commodity-usb-software-defined-radio-modules-as-an-rf-debug-tool/

author: KE5FX
author_rank: Super Contributor
timestamp: October 07, 2023, 06:15:11 pm
content: Absolutely. Receiver designers have always wanted to use high-dynamic range front ends with digital back ends. This goes back to the 1984-eraCollins HF-2050at least, and I wouldn't be surprised if the boffins at Racal were either hot on their heels or even ahead of them.The problem with a tuned RF+DSP IF solution is that you miss out on one of the big wins with DSP, which is the ability to acquire, store, and process the whole spectrum of interest at once. The best modern ADCs have enough dynamic range to be connected directly to the antenna without making a complete mess of the spectrum, although you won't find them in USB dongles or cheap SDRs, and some front-end filtering is still going to be needed for use near high-powered transmitters. It's just a question of what you consider more important in a given installation.

author: A.Z.
author_rank: Super Contributor
timestamp: October 07, 2023, 10:01:15 pm
content: @KE5FXtotally agreed, and the SDR units you're referring to, aren't the cheap dongles, but stuff like thesehttps://www.ettus.com/products/or ... better

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 07, 2023, 11:11:08 pm
content: The key factor in the description is cheap. You can go have one monitoring all the spectrum you want, perhaps zeroing in on some strong signals in an area you don't want to focus on, and then spend your real shekels on on a receiver that suits your areas of high interest. Those cheap SDRs are not bad, just limited in their area of suitability.

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 08, 2023, 07:51:12 am
content: Thanks everybody for making me feel like I wasn't asking a stupid question, or overlooking something obvious.@CatalinaWOWThe link I used for background made the interesting point that due to the limitation of the I/Q data rate (hence ADC operation etc.) the bandwidth was limited, and in his application he'd relied on the SDR software to (adjust any "front end" and) stitch data together.Now I obviously go back to the days when a wireless had a band switch with a discernible clunk as different combinations of windings and components were switched in (let's leave pluggable coils out of it). That suggests an issue in itself, since while a physical switch in an RF data path is hardly ideal, neither is any attempt to replicate it using FETs. However focusing on that, it's interesting to ask oneself what actually one's being sold when one looks at a fancy modern receiver with buttons and switches- or even with buttons and no switches.I believe that- as an example- some of the newer Icoms now support I/Q outputhttps://www.change.org/p/icom-inc-please-add-i-q-out-via-usb-to-icom-ic-7300(which I believe was heeded) and I presume that something like an RTL chip could be retrofitted to an older communications receiver rather in the tradition of the "discriminator tap" used by those with an interest in POCSAG and similar protocols.Unfortunately the bands I'm interested in are outside the conventional .15-30MHz range handled by the relatively affordable GCRs which are arriving on the market in sadly increasing numbers as their owners migrate to a higher plane :-( But there does appear to be a "new generation" of receivers with coverage from the 100s of kHz to low GHz which might be ripe for exploitation: even if whatever's in their RF frontend is electronically switched.MarkMLl

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 08, 2023, 08:35:13 am
content: Quote from: A.Z. on October 07, 2023, 10:01:15 pmAlthough I bet that an Ettus with a properly-configured antenna would acquit itself reasonably when compared with a high-end GCR using a bit of coat hanger.MarkMLl

author: A.Z.
author_rank: Super Contributor
timestamp: October 08, 2023, 09:18:20 am
content: Quote from: MarkMLl on October 08, 2023, 08:35:13 amnope, just consider that the purpose for those high end SDR units is different and then the received bandwidth (160MHz or more) can be processed using software; a GCR would stand light years behind, add the fact that those SDR units can be networked/clustered and geographically located far away each other...Just to have a very coarse idea about the matter, try having a look at thishttps://redhawksdr.org/https://redhawksdr.org/2.2.7/getting-started/and the above is just a fraction of what can be doneOh and in case you wonder, check herehttps://code.nsa.gov/

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 08, 2023, 09:50:54 am
content: @A.Z.Well, I am- /obviously/ aware of the potential of SDR technology (and of projects such as GNU Radio) for demodulation and decoding.What I'm trying to highlight is the extent to which most available implementations skimp on the frontend (sometimes intentionally, in order to implement a "panadapter" style display), and query the extent to which a hybrid approach would be an improvement.MarkMLl

author: A.Z.
author_rank: Super Contributor
timestamp: October 08, 2023, 10:21:14 am
content: I see, well, the current commercial (cheap) SDR aren't up to the "state of the art", most of them lack the needed AD resolution, the only cheap ones which are a bit better are those based on Mirics (MSI) chips

author: radiolistener
author_rank: Super Contributor
timestamp: October 08, 2023, 02:14:04 pm
content: Quote from: A.Z. on October 08, 2023, 10:21:14 amMirics chip is not better, it is worse than RTLSDR. Mirics has a lot of parasitic spurs, dead frequencies, noisy LO and terrible frequency beats. I have both, but almost never use Mirics, due to worse signal quality.

author: radiogeek381
author_rank: Regular Contributor
timestamp: October 08, 2023, 02:16:05 pm
content: Echo the comments about dongles vs. more sophisticated gear. I know folks who have used them for panadapters, tapping off the IF stage of a yeasu 817, but the 8 bit ADC limits the usefulness.I own two Ettus USRPs: An N200 with an RF deck that goes from 10MHz to 6GHz, and a B210 that goes from 70 MHz to 6GHz.The N200 has a 40 MHz A/D. The B210 something like that. In any case, the bandwidth is sufficient that I can use the N200 in the 80m band, and the B210 on 6m. But all of them require a front-end filter.I originally bought the N200 to use as an IF rig for a 10GHz transverter and to learn SDR by doing something really ambitious: implementing an all mode transciever. I used it as a transverter a lot, and learned a lot. I've also used it on HF for WSPR, JTxx, and even SSB. In all cases, there was a filter in the path. In most, there was an outboard TX amplifier. I've been using the Ettus UHD library for all the programming. The documentation is weak, but I've come to terms with it. The transceiver software has bitrotted a little, as I haven't had time to maintain it. Sigh.I've never really understood how the "capture the whole band" folks don't end up compromising intermod. Beyond that, the atmospheric/environmental noise at 3MHz is pretty loud and a bunch-o-dB louder than on 20m. Those should compromise performance, but my friends who own Flex Radios are quite happy with them.I use the 40MHz sample rate to extend the tuning range, but downsample the bejeebers out of it (to 625 kHz) for the link to the computer. In practice, I put the front end RF oscillator about 200 kHz above the frequency of interest, and use the digital down converter on the radio to tune over a fairly narrow range (about 100kHz, I think). This puts the DC spike out of the panadapter's window, and keeps it way away from the demodulators. At 625 KS/s the input data rate is manageable -- the software can run on a 10 year old laptop and have cycles left over. It also allows relatively simple frequency domain resampling as the ratio is "only" 625/48.The sensitivity far exceeds the dongle class, and the N200/UBX has a 40 MS/s 14 bit I and Q A/D, vs. 12 bits for the B210 and 8 bits for the HackRF.The newer series of radios from NI/Ettus are truly spectacular. The N320 and the X3xx series are beasts. But they come with a beastly price. (north of $20K) 200 MS/s, full bandwidth back to the computer (twin 10Gb/s links), 14 bit ADC.So, you get what you pay for. And now the Ettus boxes are *really* expensive. The N200 will still outperform the Pluto's and the HackRFs of the world, but the B210 might not be compelling. I'm beginning to experiment with the others, but the lack of HF transmit for them will limit their applicability until I can build some outboard filtering as well.

author: radiolistener
author_rank: Super Contributor
timestamp: October 08, 2023, 02:21:44 pm
content: most of modern sdr are overpriced. This is just a speculation due to problems with chips availability and sdr popularity. Real price for a good DDC transceiver with 12-16 bit ADC running at 122 MHz is about 100 USD, not include power amplifier. But you can find that they are selling now at 200-300 USD and some sellers even rise price to non adequate 500-1500 USD, for thing which components cost just 50-100 USDCurrently there is a problem to order FPGA chips, so the price for sdr receivers which use it is multiplied by 3..Regarding to models, almost all devices which using high speed ADC chip has enough performance to beat all these cheap dongles on RTL/Mirics. It doesn't matter much 12, 14 or 16 bit is used, because their performance is almost the same, it needs expensive oscillator and good RF frontend to see a small diference between 12 bit and 16 bit. But I'm talking about dedicated high speed ADC chips, not about these marketing "14 bit" bullshit dongles, which actual performance is worse than 8 bit dedicated high speed ADC.

author: radiogeek381
author_rank: Regular Contributor
timestamp: October 08, 2023, 06:23:39 pm
content: QuoteMy Ettus USRP N200 *always* outperforms the AOR 5000 on the desk next to it -- as long as it has a filter in the line to the antenna.

author: radiolistener
author_rank: Super Contributor
timestamp: October 08, 2023, 06:40:46 pm
content: Quote from: radiogeek381 on October 08, 2023, 06:23:39 pmthe filter add at least 1-2 dB attenuation, so the signal going below atmospheric noise and cannot be recovered... You can add preamplifier before filter to avoid it, but it will reduce dynamic range... So there are pros and cons of that filter...There is no sense to process 160 MHz bandwidth in software, because it just waste CPU power. It can be done on FPGA side.

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 09, 2023, 08:52:13 am
content: Quote from: radiolistener on October 08, 2023, 06:40:46 pmOK, so I think that takes us back to my tentative position ** : (a) an SDR can benefit from a tuned frontend except where a broadband panoramic display is expected, and (b) semiconductor technology has improved over the last couple of decades which means that something like an AOR 5000 is no longer state-of-the-art.So do the advances in semiconductor technology etc. mean that these days a better RF frontend could be built, or would we be getting into "silly technology" i.e. ceramic substrates and cryogenic cooling in order to match what's on a high-end chip?Or do we have to accept that receiver design has bifurcated with (on the one hand) conventional technology which can tease a weak signal out from the background noise and (on the other) SDRs which can show the broadband situation at a glance but might not be quite as good at getting the detail?** Obviously acknowledging that I'm talking to people here with vastly more practical experience and theoretical knowledge than I can muster.MarkMLl

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 09, 2023, 08:59:42 am
content: Quote from: KE5FX on October 07, 2023, 06:15:11 pmSo the obvious question there is whether frequency hopping as used in Bowman etc. relies on a single broadband frontend, or if there is in fact an element of electronic retuning involved (i.e. varicap diodes etc. rather than just telling a DSP to use different parameters).MarkMLl

author: radiolistener
author_rank: Super Contributor
timestamp: October 09, 2023, 02:14:30 pm
content: Quote from: MarkMLl on October 09, 2023, 08:52:13 amSDR is the best on IF processing side, because it is flexible, don't requires expensive and hard tune components and allows to implement better low pass filters. And IF processing doesn't require high computation performance, it can be done on a usual MCU or CPU.Attempt to use SDR for direct RF processing leads to a limited RF bandwidth due to CPU/DSP performance limitations, high power consumption and very high price for such solution.This is why for HF you can use Digital Down Conversion (DDC) receiver, but for VHF and UHF it's more optimal to use analog down converter on the RF frontend.

author: radiolistener
author_rank: Super Contributor
timestamp: October 09, 2023, 02:25:23 pm
content: Quote from: MarkMLl on October 09, 2023, 08:52:13 amIt depends on what ADC chip you're using. If you're using high end state-of-the-art ADC chip for DDC in HF band, adding additional components on it's input can lead to performance degradation. But if you're using cheap low cost ADC, it's specification is not good and using additional filters/amplifiers on RF frontend can improve results.

author: tggzzz
author_rank: Super Contributor
timestamp: October 09, 2023, 02:29:52 pm
content: Sampled analogue processing can be much lower power than sampled digital processing, and can have stunning performanceN-path a.k.a. commutating capacitor filters have some rather interesting properties in this area, e.g. bandpass filter with Q>1000 and falloff rates >10000dB/decade, made from 10% components.See also "Tayloe mixer" for some other examples.On this forum, maywatt has written several useful posts hinting at their virtues.

author: radiogeek381
author_rank: Regular Contributor
timestamp: October 10, 2023, 01:13:34 am
content: I think the if I put a narrowband filter in front of the AOR it might rise to the USRP -- it's design was a compromise between large tuning range and performance.But the IF in the AOR leaves a bit to be desired. That's where SDR really shines. If you can get the signal through the front end without intermod, birdies, and all the other bad things that can happen, the ability to implement good filters (tight but not irritating to the human ear) can make a big difference.BTW -- a big difference between inexpensive SDRs vs. more expensive units is the amount of control provided for the signal chain. This is especially useful in setting the front-end LO frequency and controlling the (analog) synthesizer that drives the mixer between the antenna and the ADC.

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 10, 2023, 08:01:03 am
content: Quote from: radiogeek381 on October 10, 2023, 01:13:34 amSo if I'm reading people correctly, basically tacking a high-speed ADC onto IF output and processing a signal at something like 455kHz or 10.7Mhz.This rather takes me back to the 1950s projects which described how to scavenge various IF strips etc. from ex-military receivers and hook them up as a televisor :-)MarkMLl

author: KE5FX
author_rank: Super Contributor
timestamp: October 10, 2023, 07:30:56 pm
content: Quote from: MarkMLl on October 10, 2023, 08:01:03 amFarther back than that.

author: fourfathom
author_rank: Super Contributor
timestamp: October 10, 2023, 08:09:35 pm
content: I'm involved with a bunch of folks who are using the KiwiSDR and the RX-888 SDR receivers for multiband reception of amateur modes such as WSPR and FST4W, looking at ionospheric propagation behavior (seehttps://hamsci.org/andhttp://wsprdaemon.org/). These SDRs have a wide-open front-end, feeding a high-speed digitizer and then a high-speed USB connection. Phil Karn's "ka9q-radio" is one of the software systems used to decode and measure the full HF spectrum. Pretty amazing stuff, but you need a high dynamic range ADC for this to work well.About lower-frequency signals overloading the SDR front-end, many are using a shelf filter to better fit the nature of the signals found across the spectrum. Also, you want a good anti-alias filter to reduce the effects of broadcast FM and low-VHF service signals -- the built-in filters on these SDRs may not be good enough, especially if you reduce the SDR sample rate (for thermal and processing reasons). I've designed a little shelf/LPF filter that is getting good reviews. The design is pretty simple:If you want more info on this filter it's on the website:https://turnislandsystems.com/sdr-front-end-filter/

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 11, 2023, 03:37:33 pm
content: Quote from: KE5FX on October 10, 2023, 07:30:56 pmPartial recreation of SIGSALY... nice :-)MarkMLl

author: jonpaul
author_rank: Super Contributor
timestamp: October 11, 2023, 04:24:45 pm
content: My IEEE Spectrum article of 2019 was reconstruction ONLY of one of 72 6 level ADC ("steppers" ) used to quntize the 12 Dudley VOCODER paramentes and true random noise keys used for unbreakable speech scrambing.See the many artilecs on SIGSALY.links for my IEEE articles.(cited in previous post)https://spectrum.ieee.org/rebuilding-a-piece-of-the-first-digital-voice-scrambler(added art on debugging and circuits)https://spectrum.ieee.org/sigsaly-analogtodigital-converter-construction-and-debugging(Sept 2021 9 pages feature and cover)https://spectrum.ieee.org/the-scandalous-history-of-the-last-rotor-cipher-machineYour comments appreciated!Jon

author: jonpaul
author_rank: Super Contributor
timestamp: October 11, 2023, 04:27:13 pm
content: Main difference is Images, 3rd order IM, front end overload.A triple conversion superhet is the gold standardJ

author: MarkMLl
author_rank: Frequent Contributor
timestamp: October 12, 2023, 08:15:40 am
content: Quote from: jonpaul on October 11, 2023, 04:24:45 pmI have a certain appreciation of veteran technology, and was once privileged to work with somebody who'd been at Manchester in the early days of computing. I don't know exactly which machine(s) he worked on but he recounted that he once caused a stir by building a 2Kword memory.MarkMLl

author: A.Z.
author_rank: Super Contributor
timestamp: October 12, 2023, 09:54:54 am
content: Quote from: radiolistener on October 08, 2023, 02:14:04 pmI was referring to dynamic range, which for SDR units is directly related to the number of bits used in the AD

author: A.Z.
author_rank: Super Contributor
timestamp: October 12, 2023, 09:56:08 am
content: Quote from: radiolistener on October 08, 2023, 06:40:46 pmThe Ettus CAN process up to 160MHz at once, but it's NOT mandatory... did you ever try one of those ?

author: A.Z.
author_rank: Super Contributor
timestamp: October 12, 2023, 10:11:13 am
content: Quote from: radiogeek381 on October 08, 2023, 02:16:05 pmWell, if one can accept some limitations but still wants "better than those cheap SDR dongles" performances there are "mid range" products too, like for examplehttps://winradio.com/home/receivers.htmhttps://www.eladit.shop/en-gb/RADIO-SDR-c53003380sure, those aren't up to par with receivers like the Ettus ones, but are FAR better than the usual "dongles" then it all depends from what one wants to use an SDR unit for

author: radiolistener
author_rank: Super Contributor
timestamp: October 13, 2023, 12:34:36 am
content: Quote from: A.Z. on October 12, 2023, 09:54:54 amNo, dynamic range includes ADC bits and bandwidth (ADC sample rate). This is incorrect to compare ADC bits with no take into account working bandwidth.For example RTLSDR uses 9-bit ADC (SNR=9*6.02+1.76=55.94 dB) running at 28.4 MHz. When you downsample it to 2.7 kHz SSB, the dynamic range will be increased for 10*log(28400/(2*2.7))=37.2 dB. So the dynamic range of RTLSDR is about 55.94+37.2 =93.4 dB for SSB mode. Which is equals to (93.4-1.76)/6.02=15 bits ENOB.For comparison Mirics ADC has 12 bit resolution (SNR=12*6.02+1.76=74 dB) at about 250 kHz sample rate. When you downsample it to 2.7 kHz SSB, the dynamic range will be increased for 10*log(250/(2*2.7))=16.6 dB. So the dynamic range of Mirics is about 74+16.6 =90.6 dB for SSB mode. Which is equals to (90.6-1.76)/6.02=14 bits ENOB.As you can see, Mirics has a little bit worse dynamic range than RTLSDR, RTLSDR has about 3 dB better dynamic range.Of course these calculations don't include some losses on noisy LO implementation (Mirics has much worse LO than RTLSDR), bit rounding and other processing thing. But RTLSDR has better performance than Mirics. The only con of RTLSDR is that it don't allows to get 8 MHz bandwidth IF. But this is not needed for a good receiver, 3.2 MHz of RTLSDR is good enough. Most of the time I'm using 2.4 MHz and it is good enough.

author: A.Z.
author_rank: Super Contributor
timestamp: October 13, 2023, 02:53:25 pm
content: Quote from: radiolistener on October 13, 2023, 12:34:36 amIf my memory is serving me correctly (and I think it does), the MSI001/MSI2500 sample rate is between 5MHz and 8MHz, not 256KHz (where does that come from ?)

author: radiolistener
author_rank: Super Contributor
timestamp: October 13, 2023, 07:27:22 pm
content: Quote from: A.Z. on October 13, 2023, 02:53:25 pmYes, but it reduces dynamic range for sample rate 5-8 MHz. It's hard to say what exactly mode it uses internally, because this information is not disclosed. But their 12 bit dynamic range is specified for lowest bandwidth which is about 250 kHz. Unfortunately they are showing marketing bits which already include downsample dynamic range gain and there is no information about original ADC specification.It seems that they hide it because don't want to show real comparison with RTLSDR specificationAnd since Mirics using more noisy LO than RTLSDR, it doesn't matter what is dynamic range of their ADC, because dynamic range will be limited with noise of LO.And after all, Mirics requires to use proprietary driver which is unstable and have many issues with multi-threading and other things. So, this is just a headache to use Mirics, with no any benefits against stable driver for RTLSDR.For example just compare DC offset of RTLSDR and Mirics. RTLSDR DC offset can be completely filtered with IIR filter with 1 Hz cutoff. Mirics DC offset cannot be filtered even with 100 Hz bandwidth. It shows that Mirics have very dirty and noisy DC offset.So I just don't understand why people still using it

author: A.Z.
author_rank: Super Contributor
timestamp: October 14, 2023, 05:43:28 am
content: the MSI3101 chipset (MSI001+MSI2500) has 10bit ADC resolution at/above 5MHz rate and can use 12bit resolution below 5MHz rate, at least according to the docs released by Mirics and to the various Linux drivers implementations so, again, I can't see where that "khz" sample rate you referred comes from

author: pienari
author_rank: Regular Contributor
timestamp: October 14, 2023, 03:42:28 pm
content: SDRplay RSP1A works just fine.Cheap RTL2832u + 820T2 set i could not receive EFOU_ATIS transmitter 135.450MHz AM 28km from airport.Rx takes too much interference from FM broadcast transmits 10km away.With RSP1A EFOU_ATIS 135.450MHz signal is loud and clear S7 to S8.But what i could not believe with RSP1A i can receive FM radio broadcast from Sweden, 160km to transmitter and signal is S9+30bd with 180khz bw. RDS.

author: radiolistener
author_rank: Super Contributor
timestamp: October 14, 2023, 05:27:25 pm
content: Quote from: A.Z. on October 14, 2023, 05:43:28 amyou're confusing resolution, ADC bit resolution is fixed and specified for specific hardware bandwidth of ADC. It doesn't have sense if bandwidth is not specified. For SDR receiver bit resolution is specified for hardware ADC bandwidth, it should not include processing gain.There is no such information about Mirics chips in published documentation. They hide this information. The "resolution" you're talking about is different thing, it already includes processing gain. This is just marketing stuff and don't have sense to talk about it if you want to compare it with other devices.Quote from: pienari on October 14, 2023, 03:42:28 pmDon't confuse ADC performance with presence of input filter. These are different thing. You can get better result with RTLSDR just by adding proper filter on it's input. SDRPlay has such filters inside, but it don't improve it's performancem, it just helps to compensate low dynamic range of SDRPlay ADC by cutting off strong signals.Good ADC has good dynamic range performance and can work with no issues with presence of strong out-of-band signals on it's input. It doesn't requires additional filters, just because it's dynamic range is high enough to not overload ADC with strong signals at maximum sensitivity.Adding filters to good ADC just reduce it's sensitivity because filter has some signal loss. So it won't give you advantage, on the contrary - adding filter make signal worse...If you're still want to use filters with high performance ADC, you're needs to use extra high quality filter with ultra high Q-factor components, proper layout and soldering. Even type of PCB, mask and solder materials can affect results... Such filter will cost more than ADC and cannot provide you with significant improvement on high performance ADC.

author: pienari
author_rank: Regular Contributor
timestamp: October 14, 2023, 05:42:48 pm
content: Well that is bad if there have to be band pass filter every frequence what to listen.RTL BW is usable only 2.5MHz vs. RSP1A 10MHz.I measured RSP1A NFM sensitivity.Rx 2.5khz600kHz 4.3uV snr 10db1.2MHz 2.1uV snr 10db3.4MHz 0.95uV snr 10db6.8MHz 0.78uV snr 10db10.4MHz 0.8uV snr 10db14.6MHz 0.6uV snr 10db18.2MHz 0.6uV snr 10db22.8MHz 0.6uV snr 10db25.9MHz 0.55uV snr 10db29.5MHz 0.55uV snr 10db47.0MHz 0.55uV snr 10db56.3MHz 0.62uV snr 10db61.0MHz 0.27uV snr 10db102MHz 0.33uV snr 10db145MHz 0.33uV snr 10db205MHz 0.30uV snr 10db435MHz 0.24uV snr 10db835MHz 0.21uV snr 10db1040MHz 0.24uV snr 10db1040 is top of my signal generator.

author: radiolistener
author_rank: Super Contributor
timestamp: October 14, 2023, 05:47:42 pm
content: Quote from: pienari on October 14, 2023, 05:42:48 pmThat is usual misunderstanding.As I said before, RTLSDR ADC working at 28.8 MHz, it means that it's ADC has bandwidth 14.4 MHz. This is more than 10 MHz2.4 MHz is IF bandwidth after processing. Actually RTLSDR allows IF up to 3.2 MHz.There is no sense to have so wide IF bandwidth. 1-2 MHz is good enough.Quote from: pienari on October 14, 2023, 05:42:48 pmAccording to my tests RTLSDR has much better sensitivity on 145 MHz band, it can receive very weak signals when Mirics is already flooded with noises.At HF band they have the same sensitivity, but Mirics has many dead frequencies and more spurs. RTLSDR has mirrors around 14.4 MHz, but it can be fixed with filter or external up converter. This issue is already fixed in RTLSDRv4.

author: pienari
author_rank: Regular Contributor
timestamp: October 14, 2023, 06:04:48 pm
content: I have old AOR 8200 mk2 and i have compared it to SDR . I don't need AOR anymore , SDR outperforms

author: radiolistener
author_rank: Super Contributor
timestamp: October 14, 2023, 06:10:47 pm
content: Quote from: pienari on October 14, 2023, 05:42:48 pmI think this is a bad idea to measure sensitivity with FM modulation, because it has non linear properties, so you can get strange results. It's better to use SSB or CW for that. Usually sensitivity is measured with 2.7 kHz bandwidth for SSB and 500 Hz for CW.

author: fourfathom
author_rank: Super Contributor
timestamp: October 14, 2023, 06:11:46 pm
content: Sometimes you just can't use a narrow front-end filter. I had mentioned the RX-888 and external shelf / anti-alias filters up-thread (https://www.eevblog.com/forum/rf-microwave/cheap-sdr-devices-vs-classical-communications-receivers/msg5106288/#msg5106288), used in full-spectrum reception. I know several people who are running this setup during today's eclipse, for propagation studies. The RX-888 is receiving the full 0-30 MHz spectrum (the only front-end filter is the shelf/LPF), at a sample rate of around 66 MHz and sending about 128 MBytes per second over the fast USB connection to the computer. Using a 3.5 TByte drive they can record six hours of full-spectrum data for later analysis.

author: radiolistener
author_rank: Super Contributor
timestamp: October 14, 2023, 06:14:15 pm
content: Quote from: fourfathom on October 14, 2023, 06:11:46 pmomg, this is a waste of disk spacebut if I had a 3.5 TB disk I would try

author: pienari
author_rank: Regular Contributor
timestamp: October 14, 2023, 06:49:21 pm
content: Quote from: radiolistener on October 14, 2023, 06:10:47 pmWell .. if you have such devices, would you please make some measurements for us?

author: A.Z.
author_rank: Super Contributor
timestamp: October 14, 2023, 07:38:04 pm
content: Quote from: pienari on October 14, 2023, 06:49:21 pmthat would be really interesting, also since the results, if unbiased, could reveal a lot of things

author: radiolistener
author_rank: Super Contributor
timestamp: October 15, 2023, 12:43:50 am
content: Quote from: pienari on October 14, 2023, 06:49:21 pmYes, I can do, but I don't have good signal source, just Chinese PSG9080 and Si5351 and ADF4351. I have attenuators, so can make any signal level, but the PSG9080 output is not so clean and Si5351 / ADF4351 has square wave which may affect results for some tests.What kind of measurement do you want to see?