hybridfree/eevblog-posts huggingface dataset:
very large array detection distance? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2023, 01:08:46 am
content: I see that for optical telescopes its very easy to get a maximum range from google.But for radio telescopes, not so easy.Does anyone know? Like how many lightyears can it see?

author: radiolistener
author_rank: Super Contributor
timestamp: April 25, 2023, 01:29:45 am
content: what do you mean when you saying "very easy to get a maximum range from google"?

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2023, 01:35:15 am
content: search james webb furthest distance and very large array furthest distance , whichever way you feel like phrasing itas in 'maximum distance of resolving stellar objects' , usually specified in light years

author: 0culus
author_rank: Super Contributor
timestamp: April 25, 2023, 02:11:36 am
content: In either case, the largest distance depends on the electromagnetic radiation reaching us. Maybe a better way to ask this is, what is the weakest signal the VLA can detect? See:https://science.nrao.edu/facilities/vla/docs/manuals/oss2016A/performance/sensitivity

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2023, 02:23:15 am
content: can it detect anything that james webb can't distance wise?(µJy/beam) raised my confusion level

author: cj
author_rank: Contributor
timestamp: April 25, 2023, 06:32:14 am
content: I suspect it can see the CMBR (Cosmic Microwave Background Radiation) at a distance of over 13 billon lightyears, not a stellar object though.CJ

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 25, 2023, 08:40:52 am
content: Apples and oranges? Radio telescopes don't have a sensor like in an optical device, there's no megapixels or whatever, they can only see one spot or 'pixel'. To create a map of any kind the radio telescope has to scan or look around. Would be an interesting idea to try to emulate an optical sensor though, however I think if you could create an RF lens of some kind it would have a very limited bandwidth.

author: cj
author_rank: Contributor
timestamp: April 25, 2023, 03:02:17 pm
content: Focal-plane arrays (you can see this as multiple pixels) are widely used in radio telescopes.The Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands also uses Focal-plane arrays.I don't know if the VLA uses them, haven't checked.The dish of a radio telescope is the lens or part of a multiple lens system (dish+sub reflectors) .CJ

author: mjj
author_rank: Contributor
timestamp: April 25, 2023, 06:55:40 pm
content: There is lots of good information on the Square Kilometer Array (https://www.skao.int/en) and LOFAR websites (https://www.astron.nl/telescopes/lofar/) which are the two largest radio telescopes either under construction (SKA) or built (LOFAR)
Anritsu MS2668C Spectrum analyzer - Page 1
Forum section: electronics / rf-microwave

author: Sabby
author_rank: Newbie
timestamp: April 20, 2023, 10:26:13 am
content: I am using an MS2668c spectrum analyzer for my work and I need to save some data so that I can use it in my work. There is a memory card installed in the spectrum analyzer. After reading the manual I am doing every step mentioned, but while I press the save media button one new message is coming up "Media type is different" and nothing is saved in the memory card. I just have no clue how to fix this issue. Kindly help me if anyone knows anything.Thanks in advance.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 20, 2023, 08:27:04 pm
content: if it is formatted to FAT32 try to format it to FAT16.

author: Bicurico
author_rank: Super Contributor
timestamp: April 20, 2023, 08:39:25 pm
content: Try to format the memory card.

author: Stray Electron
author_rank: Super Contributor
timestamp: April 20, 2023, 10:20:38 pm
content: If it uses a PCMCIA card it most likely has to be a Static Ram type memory and not Flash memory. The LeCroy scopes will only use the Static RAM cards that have a backup battery on the card and I know that some other equipment is the same way.
Are there any PCB shielding cans at a reasonable price? - Page 1
Forum section: electronics / rf-microwave

author: djsb
author_rank: Super Contributor
timestamp: April 13, 2023, 02:46:23 pm
content: I've been looking for a 50 mm x 50 mm x16mm and 100 mm x 50 mm PCB mounted PCB shielding can with a lid. The only ones I've found that are close to these sizes are Parancea PFL6T and PFL9T. Parancea are OK, and it helps that they are local to me in the UK and available on RS and Farnell. But I'm just wondering if there is any other choice as they are a bit pricey. Any suggestions? Thanks.

author: M0HZH
author_rank: Regular Contributor
timestamp: April 13, 2023, 03:54:34 pm
content: I used Harwin for a couple of products, but they were smaller than what you need. On the expensive side but good quality. TE Connectivity and Wurth were also candidates.Later I found out that more serious PCB manufacturers should be able to offer custom shielding as well. Worth asking.

author: LM21
author_rank: Regular Contributor
timestamp: April 16, 2023, 05:41:28 am
content: Something like these from Digikey?https://www.digikey.fi/en/products/detail/harwin-inc/S0911-46R/10059434https://www.digikey.fi/en/products/detail/harwin-inc/S02-20150300/4953269These are what I have saved, DK has other models too.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: April 16, 2023, 05:51:44 am
content: Have a look at Reichelt UK and search for TEKO 3710.

author: KE5FX
author_rank: Super Contributor
timestamp: April 16, 2023, 06:32:33 am
content: I use a lot of LeaderTech SMS-xxx shields with removable covers, no complaints. Also a few of the Laird BMI-S-xxx parts.Quote from: karpouzi9 on April 16, 2023, 05:54:42 amFotofab is a popular choice for that.

author: n4u
author_rank: Contributor
timestamp: April 16, 2023, 07:37:55 am
content: Do you want to make a production of it ? If you dont - u may make a cheap fr4 laminate or weld box by yourself.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 16, 2023, 08:51:10 am
content: I've used Teko (https://www.teko.it/en/products/family/RF). Good quality, easy to solder, and at the time, relatively inexpensive. That was several years ago.

author: jc101
author_rank: Frequent Contributor
timestamp: April 16, 2023, 11:02:16 am
content: Quote from: djsb on April 13, 2023, 02:46:23 pmAnything in the Wurth lineup be suitable? I have a rep visiting next week and could blag some sampleshttps://www.we-online.com/en/components/products/pbs/emc_components/emi_shielding_material

author: djsb
author_rank: Super Contributor
timestamp: April 16, 2023, 12:14:43 pm
content: I'll keep the Wurth link for future reference. I've managed to get 4 of PFL6T cans off of eBay for cheaper than usual, which will do for my prototypes. Thanks everyone for all of your helpful replies.

author: jonpaul
author_rank: Super Contributor
timestamp: April 16, 2023, 12:19:17 pm
content: Why do you need a shield can?perhaps a circuit mod can fix any interference or EMI issuesjon
SI4743 radio ic antenna input circuitry  - Page 1
Forum section: electronics / rf-microwave

author: franksterb92
author_rank: Contributor
timestamp: April 10, 2023, 04:12:02 am
content: i know there are examples in the datasheet for some band antenna circuits but im wondering how to do a AM/SW/LW/FM/WB circuit so all the bands that chip is compatible with

author: franksterb92
author_rank: Contributor
timestamp: April 10, 2023, 07:10:52 am
content: ok ive ben working on what i think will work at least from looking at the app notes. from what i see in one it just switches in a 4.7uh inductor into the am antenna input of the si4743 ic please leave feedback as im no rf engineer

author: franksterb92
author_rank: Contributor
timestamp: April 11, 2023, 09:48:30 am
content: ive ben researching and from what i can tell and from looking at the si4743 data sheet at the block diagram that the antenna inputs lead right to the LNAs inside the radio ic so what the antenna circuit needs is a band pass filter to filter out unwanted frequency so in the case of am something like 520-1710KHZ and fm 64-108MHZ how would i scientifically test something like this

author: A.Z.
author_rank: Super Contributor
timestamp: April 16, 2023, 08:37:11 am
content: Quote from: franksterb92 on April 11, 2023, 09:48:30 amwell, design your filter using thishttps://rf-tools.com/lc-filter/and then build and test it
KENT EK-4 vs KENT EK-4M cw keyer - Page 1
Forum section: electronics / rf-microwave

author: PA3BBV
author_rank: Contributor
timestamp: April 04, 2023, 08:13:25 am
content: Hello all,I own the KENT EK4 CW keyer. This keyer can be upgraded to a memory keyer EK4M. It is said that a memory chip eeprom must be inserted. An 8-pin IC socket is available on the printed circuit board. I assume that it needs a serial eeprom.Does anyone have a similar keyer with the memory expansion? It would also be nice if he took a look at the print to see which 8 pin ic is on it.I would really appreciate that. leo

author: Egil - LA2PJ
author_rank: Newbie
timestamp: April 11, 2023, 05:24:55 pm
content: Suggest you try to contact the manufacturers:https://www.kent-engineers.com73Egil
HP 8753 VNA Owners please help with data export - Page 1
Forum section: electronics / rf-microwave

author: rfspezi
author_rank: Regular Contributor
timestamp: March 21, 2023, 07:34:11 pm
content: When i save a measurement on my HP8753E to the floppy disk the Smith chart on the VNA screen looks different to the one stored on the floppy drive.Here the Smith chart shown on the VNA screen:Here the Smith chart shown on my PC (data on the floppy disk):I save the measurement with "DATA ONLY ON" set and "SAVE STATE".I suspect that the data on the floppy may be the RAW values or at least not corrected?Here is what the manual says:Can anybody help on how to correctly save the data to the floppy step-by-step?ThanksThe file i get is called "DATA00.D1".Can it be i need to use the "FORMATTED" version "DATA00.F1"?

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: March 22, 2023, 05:11:12 am
content: Quote from: rfspezi on March 21, 2023, 07:34:11 pmIt's been 25 years since I pulled data from an 8753, and then it was through HP-IB, but I believe the stored data is raw data, with no correction and no formatting. You can double check by turning correction off on you 8753 and see if it matches the DATA00.D1 data. So use F1 data but be sure to have the format in Smith or Polar or I don't think you get the complex data

author: rfspezi
author_rank: Regular Contributor
timestamp: March 22, 2023, 08:14:54 pm
content: QuoteThank you Joel for your reply!When you say that i have to make sure that the format is in Smith or Polar, you mean the format that is displayed on the VNA screen when saving the data to disk?

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: March 26, 2023, 10:52:23 pm
content: I believe I recall that you had to be in a polar or smith to get complex data in the data buffer. But it really has been maybe 25 years since I have used an 8753.

author: rfspezi
author_rank: Regular Contributor
timestamp: March 27, 2023, 07:43:31 am
content: You are absolutely correct!My workflow, to get the corrected complex data out of the HP 8753E, looks like this now:Set the 8753 to display measurement data in Smith formatPerform measurementSave/Recall --> DEFINE DISK-SAVE --> FORMAT ARY = "ON", DATA ONLY = "ON", SAVE USING = "ASCII", set all other options to "OFF"Save/Recall --> SAVE STATEThis writes a single file called "DATA00.F1" to the floppy containing the measured data in complex format with correction applied.[Addition:]If i'm correct, the "DATA00.D1" file contains the corrected data aswell however WITHOUT port-extension applied.

author: hydrabus
author_rank: Contributor
timestamp: April 09, 2023, 07:45:33 am
content: Hi,I do not have any solution for export on old floppy disk but for those interested I have developed a multi-platform open source application (Based on Qt) for HP8753 VNA which requires GPIB over USB interfacehttps://github.com/bvernoux/vna_qtIf anyone is interested to provide feedback or to help to improve it you are welcomeNote: I plan to add LibreCAL (which is a fully open source/open hardware VNA eCal) support to create 4 Ports LibreCAL snp files for more details seehttps://github.com/jankae/LibreCAL
Inductance required on ferrite coil antenna to cover MW band DX reception - Page 1
Forum section: electronics / rf-microwave

author: vinlove
author_rank: Frequent Contributor
timestamp: April 04, 2023, 10:21:38 am
content: I am planning to make a ferrite bar antenna for MW band reception.I have a few ferrite rods, and trying to wind wire around it.Just wondering what range of inductance is required for tuning up MW band 500 - 1700 kHz?I will be adding a variable capacitor of around 500 pF to tune the ferrite wound coil.I have already wound enamel wires around the ferrite rod, and it is reading 411 uH.But I am not sure if this value would be workable to cover MW band reception antenna.Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 04, 2023, 10:34:58 am
content: \$L = \dfrac{1}{(2 \pi F)^2 C}\$Tuning 500kHz with 500pF would require about 200uH.Band coverage is undefined as you didn't mention the capacitor's minimum value. If you use this inductance, the capacitor minimum must be (1600/500)^2 = 10.24 times smaller than max, or below 48pF, to cover it in a single range.Impedance matching will be nontrivial, as \$Z_0 = \sqrt{(L/C)}\$ is varying over the same range, meaning antenna gain and bandwidth will also vary. Probably, you just want to ensure minimum bandwidth is adequate, and make up the difference in match loss with a preamp of low enough noise level (which is quite solvable with any modern-ish JFET e.g. CPH3910). Matching might not be important at all as the common-source input impedance will be quite high (just use 100% tapping to the gate? -- give or take biasing and perhaps protection if needed), otherwise, in common-gate, the impedance will be modestly low (~25Ω?) so a fairly low tapping should be used (like, say... 4% or so?). At least, for purposes of bandwidth; I don't know offhand what the radiation resistance and gain of such an antenna is (aside from "small").Tim

author: vinlove
author_rank: Frequent Contributor
timestamp: April 04, 2023, 11:11:19 am
content: Great info. Thanks. I will get the value of the variable cap. more accurately.I better try reduce the inductance 411 uH of the coil to about half, and try tuning the band.Will update how the antenna project is progressing. cheers.
Rather Wideband Mixer Design Concern - Page 1
Forum section: electronics / rf-microwave

author: WideBandwidth
author_rank: Contributor
timestamp: April 01, 2023, 05:03:17 am
content: Hi,I'm trying to build a wideband mixer (first mixing stage of a spectrum analyzer I'm building) that takes an RF input from DC-3 GHz and spits out 3.5 GHz using an LO that sweeps from 3.5 GHz-6.5GHz. I'm trying to see if this is possible using a single-balanced configuration, but wanted some advice on the design.My current vision is as follows:An LO balun feeds two series connected diodes. The center-tap of the diodes is a combined RF-IF port that connects to a diplexer to separate out the RF and IF.The LO balun consists of a microstrip-slotline transition, and the two slotline conductors are used as the 0deg and 180deg ports that connect directly to the diodes. On this front, I've tested back-to-back microstrip-slotline transistions and am getting around 1 dB loss from around 2-8 GHz for an individual transition...not too shabby! I've also tried a single transition hooked up to the diodes with the center tap going straight to a spectrum analyzer, and am getting >30 dB LO isolation with the LO sweeping from 3.5-6.5 GHz. So far so good.On the RF-IF diplexer front, I have a suspended stripline design simulated and ready to fabricate. It achieves something like 50 dB isolation between the RF and IF frequencies (at least it does in EM simulation) using a 7th order elliptic filter (for the RF) and a 4th order coupled line filter (for the 3.5 GHz IF).Now to the actual question: If I just hook up the LO balun+diodes to the diplexer, I am suspecting I'm not going to have a good time. The reason being is that if we consider the path that the RF and IF frequencies will see, they are expecting the LO ends of the diodes to be a virtual ground, as we would have if the LO balun was an ideal transformer. This would allow the RF and IF frequencies to see the two diodes in parallel.But a microstrip-slotline transition is not an ideal transformer, and doesn't even look like a balun below 2 GHz in this case. As a result, the impedance seen by the RF and IF ports, which should ideally just consist of the diodes' dynamic impedance, will be frequency dependent due to the LO balun's own output impedance. This would naturally harm the conversion loss and cause it to flop all over the place with respect to frequency. I should note that in the particular case of a microstrip-stripline balun, the output port will look like indeed a short at very low frequencies, since the slotline portion is terminated in a short (see attachment). However, this only holds near DC, since transmission line effects will eventually turn that short into an open.So how would one go about solving this balun issue in a single-balanced mixer design? Is it even solvable given these frequency ranges? Also please correct me if I am making a mistake in my reasoning.Thanks.
Mounting wifi router on a (metal) shed wall. Do I need backing material? - Page 1
Forum section: electronics / rf-microwave

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: March 31, 2023, 06:45:05 am
content: Hi.Subject is a plain old Linksys 54G with 2 antennae that is configured as an access point. Previously located on a desk, now want to mount vertically on the interior wall of a large metal shed, about 6 feet high from the floor. Would like to know how to have it radiate inwards best and not be interfered by the metal wall behind it. Wall is ordinary Colorbond.Do I need a backing material or should I just mount it and not worry about it? Router is very old and has had a hard life. If I do need to upgrade to a wireless N or even A.C someday, how might the wall that close affect the router's performance?

author: M0HZH
author_rank: Regular Contributor
timestamp: March 31, 2023, 08:01:23 am
content: Probably it's best to have antennas perpendicular on the wall, but I wouldn't worry about it too much.It is an old slow router, you might want to upgrade to a newer one. I use a TP-Link RE305 for upstairs, it can work as a mesh / range extender, WiFi <> Ethernet bridge, DHCP server etc, does 2.4GHz & 5GHz (AC1200) and it's quite cheap (~£20 here in the UK).

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: March 31, 2023, 08:13:22 am
content: Quote from: M0HZH on March 31, 2023, 08:01:23 amThanks.QuoteYeah, it is slow. It's so old that it has a iron core tranny. It's gotta be 20 years old, and has been kept in a harsh environment continuously. I can't believe that it's still throwing punches.

author: M0HZH
author_rank: Regular Contributor
timestamp: March 31, 2023, 09:12:14 am
content: I know, they were really good back in the day and they could be flashed with OpenWRT firmware. I set up one at my dad's house, ran for about 10 years without a glitch.
Always assume 50 ohms Zin and Zout for Power Amp?  - Page 1
Forum section: electronics / rf-microwave

author: spacehen
author_rank: Contributor
timestamp: March 30, 2023, 09:20:24 am
content: I recently came across the following power amp (GRF5504) by Guerrilla RF.Link to datasheet:https://www.mouser.com/datasheet/2/777/GRF5504DS-1891813.pdfIn the datasheet there is no mention of input or output impedance of this RF PA.My question is: do we in these cases just assume it's 50 ohms?There is no matching network in the application schematic which leads me to believe that this part is internally matched to 50ohms.Regards,

author: switchabl
author_rank: Frequent Contributor
timestamp: March 30, 2023, 10:27:25 am
content: Well, it is a preliminary datasheet from a company calling themselves "Guerrilla RF", so who can say for sure? More seriously, the datasheet has a page with S-parameters that are very likely referenced to 50 ohm (unless they messed with the VNA just to confuse you) and show matching in the 450-470 MHz range.

author: spacehen
author_rank: Contributor
timestamp: March 30, 2023, 11:20:54 am
content: Thanks but I don't understand why this information wasn't included in the datasheet's front page, surely it's important? Most manufacturers state "50 ohms internally matched"Anyways... I sent their applications team an email but I'm awaiting a response...

author: switchabl
author_rank: Frequent Contributor
timestamp: March 30, 2023, 01:10:32 pm
content: Sorry, I missed the part where you thought there is no external matching network. No, it is clearly not internally matched but the application circuit shown is presumably matched to 50 ohms (M1, M2 is a simple L-match, output side is a bit more complicated, also provides DC bias). They also have a few more documents showing matching networks tuned for different frequency ranges on their website.

author: RoV
author_rank: Regular Contributor
timestamp: March 30, 2023, 01:12:34 pm
content: In the 1st page, under device description: "The device can be tuned over a range of frequencies from around 400 to 500 MHz with typical fraction bandwidths of 3 to 5%". So it definitely requires matching.I suppose S parameters are not listed only because the DS is preliminary.
Mitronics Frequency Counter - Page 1
Forum section: electronics / rf-microwave

author: SvenVE6
author_rank: Newbie
timestamp: March 29, 2023, 11:46:20 pm
content: I figured it may be a good place to ask this question. Dr. google did not return any results on this one.Mitronics MIC-1028 Frequency Counter... Ever heard about it? Scored one at a local flea market and one I got from a fellow HAM guy. One is working fine but the other has issues. As mentioned, no google infos available.Attached some pictures for the curious guys out thereVery neat little unit and probably useful for quick measurements. Perhaps someone has some history about this company, schematics or anything else...
Are S11 and S22 equal for passive matching networks? - Page 1
Forum section: electronics / rf-microwave

author: spacehen
author_rank: Contributor
timestamp: May 15, 2023, 11:42:13 am
content: Hi all,I am using MATLAB to design a matching network for a specific application. I've noticed that the tool always plots S11 and S22 the same. Am I correct to say that passive matching networks always have S11 = S22 ? Or am I missing something?For example assume you had a load with a complex impedance of 5+5i at the source side and 50 ohms at the load side and wanted to measure the reflection coefficient looking in from the source towards the load. Obviously this connection is not possible on a VNA (due to internal 50 ohms) so if S11=S22 then I can simply connect the other side of the matching network and measure gamma(in) which will give s11 or s22.

author: yl3akb
author_rank: Regular Contributor
timestamp: May 15, 2023, 01:46:32 pm
content: In general the matching networks are not reversible. You probably see that amplitudes or S11 and S22 match, but look at the phase as well.In Your case, just measure Your circuit at source side with 50Ohm VNA and 50Ohm load at load side. For perfect match, the reflection coeff. must be complex conjugate or 5-5j Ohms

author: ejeffrey
author_rank: Super Contributor
timestamp: May 16, 2023, 03:37:59 pm
content: I believe S11 and S22 are equal magnitude for passive lossless reciprocal networks. The phases aren't equal and of the network has loss the amplitude doesn't have to be either. Consider a trivial case where the two ports arent even connected internally and one port is terminated and the other is open circuit. S11 == 0, S22 == 1.

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 17, 2023, 12:14:52 pm
content: For a lossless network: |S11|^2+|S21|^2=1 and |S22|^2+|S12|^2=1For a reciprocal network: S12=S21Therefore it's easy to show that a lossless and reciprocal network has |S11|=|S22|My gut tells me this can be extended to S11=S22, but I forget the proof....Passive networks are generally reciprocal (if you're dealing with normal R/L/C components and transmission lines, not weird anisotropic materials).

author: ejeffrey
author_rank: Super Contributor
timestamp: May 17, 2023, 07:53:35 pm
content: Quote from: mtwieg on May 17, 2023, 12:14:52 pmIt's not. You can add a cable on port 1 and change the phase of S11 but not S22.

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 18, 2023, 12:40:09 am
content: Agreed, the case of the two ports being completely disconnected but with different lossless terminations (still lossless and reciprocal) easily shows that S11 and S22 can have different phase.
Wireless video transmission - Page 1
Forum section: electronics / rf-microwave

author: gascencio
author_rank: Newbie
timestamp: March 27, 2023, 10:06:27 am
content: Hi everybody,For a DIY robot, I'm trying to do wireless video transmission, around 100m.I don't know where to start for choosing emitter and transmitter.Do you know any module that can do this job? Or any IC that i can work on ?Thanks

author: Marco
author_rank: Super Contributor
timestamp: March 27, 2023, 11:45:16 am
content: The FPV drone flyers have analog and digital video transmitters on 5.8 GHz, nice high power and shouty protocols.
Measuring GHz amplifiers with Nano-VNA  - Page 1
Forum section: electronics / rf-microwave

author: szoftveres
author_rank: Regular Contributor
timestamp: March 23, 2023, 04:45:32 am
content: The problem is familiar: one wants to characterize a GHz amplifier, but -since the Nano-VNA is putting out a 0-300MHz square wave- the low-frequency high-amplitude square wave signal drives the amplifier into non-linear mode and thereby ruining the measurement.The idea is to attach a simple PI- high-pass filter to port 0 of the Nano-VNA and include it in the calibration. The VNA will now be able to supply high frequencies, without the large amplitude square wave signal. The measurements will only be useful above the corner frequency of the filter.I've made some small universal microstrip boards and built the filter on one of them. The two single-turn inductors are made from the legs of a through-hole resistor; the capacitor value is 10pf. The cutoff frequency is around 440MHz.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: March 23, 2023, 07:27:34 am
content: It might be worth it to get a more expensive but better version of the NanoVNAConsider taking a look at the LiteVNA.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 23, 2023, 12:31:19 pm
content: It's not only at higher frequencies that the squarewave can cause problems. It can also wreck havoc at lower frequencies like I demonstrated in the attached video where I look at a 1MHz amplifier.Then there is the unleveled drive, lack of programmable attenuators....... Still for less than $200, you can get the original NanoVNA along with the LiteVNA which would cover a lot of experiments. As you suggest, you just need to be aware of their shortcomings when setting up a measurement.

author: szoftveres
author_rank: Regular Contributor
timestamp: March 23, 2023, 02:13:28 pm
content: Are you suggesting that the LiteVNA is actually directly achieving e.g. 1.2GHz with its on-board generator, vs. using the 3rd or 5th harmonic of a lower frequency square-wave signal?

author: joeqsmith
author_rank: Super Contributor
timestamp: March 23, 2023, 10:31:33 pm
content: Quote from: szoftveres on March 23, 2023, 02:13:28 pmyes, read the following:https://groups.io/g/nanovna-users/message/31888

author: szoftveres
author_rank: Regular Contributor
timestamp: March 26, 2023, 04:26:38 am
content: Noted, thanks for the info about the LiteVNA.Slight improvement on the Nano-VNA filter is the capacitance reduction, from 10pf to 6.8pf.The reason is that the sqrt(L/C) impedance with 6.8pf is closer to 50ohms than with the 10pf capacitor (~35ohms). Consequently the corner frequency went up to ~ 530MHz.The result is more "rounded" corner (i.e. more damping due to better matching) and less loss at higher frequencies (the worst is -3.4dB at 1GHz).Attenuation at 300MHz is close to -20dB.
FM Radio Transmitter/Amplifier - Page 1
Forum section: electronics / rf-microwave

author: Captain Star
author_rank: Newbie
timestamp: March 25, 2023, 05:26:18 pm
content: So I purchased this online :https://www.tomtop.com/p-v6119.htmlIt's working great but the practical range is about 15 meters.I'm looking to upgrade this. The thing is, I know very little about radio frequencies and antennas.Can something like this work ?https://tinyurl.com/3zfcm9s2The device I purchased seems to have a really simplistic antenna, like a single wire.https://ibb.co/jLrLXPCAs opposed to let's say a Baofeng UV-5R witch has a more complexe antenna.https://ibb.co/grWyRs6Also if that little amplifier would work, what type of 'antenna' cable do I need, to hook it up to the HanRongDa HDR-831 ?I'm really new to RF related stuff, thank you in advance !

author: szoftveres
author_rank: Regular Contributor
timestamp: March 25, 2023, 07:01:29 pm
content: The Baofeng uv5r antenna is tuned to 144 and 440MHz, it will be inefficient for 88-108MHz (some might want to go in greater details about reflection and associated side effects, but given your experience level I won't).You'll need a good antenna, and when you get one for 88-108MHz, the range of your small transmitter will dramatically increase, without any additional amplification.A rule of thumb way of judging a whip antenna for "goodness" is by looking at it; if its length is about 1/4 wavelength of the frequency of interest (in your case 1/4 wavelength of 100MHz is ~75cm) then it's possibly good. Again, this topic is much more deeper than what a comment on a forum could be, but at least a good starting point for further studies into the vast world of antennas.Edit:I've used this style of antenna and it's quite good for the price, but is a bit different style (you have to nail it on the wall):https://a.co/d/5UJmjX4

author: geggi1
author_rank: Frequent Contributor
timestamp: March 26, 2023, 09:54:21 am
content: Use this web page to calculate a 1/4 wave antenna.https://www.southwestantennas.com/calculator/antenna-wavelength

author: Captain Star
author_rank: Newbie
timestamp: March 26, 2023, 12:40:24 pm
content: Thank you for your answer.The thing is that I want to amplify it, by a few watts.So would the device I linked in my original post work and how would I connect it to the HanRongDa HDR-831 ?If that device doesn't work, what type of device should I look into ?Also, the antenna you linked seems to be a two pole antenna (Two wires, like a + and a -)The antenna of the HanRongDa HDR-831 seems to be only one wirehttps://ibb.co/jLrLXPCI don't know the correct terminology, sorry fo the incovenience.Thank you for the insight about antennas.
Noisy Wallplug PSUs for the HF receiver - Page 1
Forum section: electronics / rf-microwave

author: vinlove
author_rank: Frequent Contributor
timestamp: March 18, 2023, 04:55:51 pm
content: I have a few 12V wallplug PSUs which plugs into the wall AC mains socket, and it gives out 12V DC.When they are used for the other devices, they are perfect - powering them and making them work.But when they are plugged into my Shortwave HF Receivers, they are the source of the hash noise in the receiver.It is very high level of static noise they cause, so that the receivers are not able to hear the weak signals.Are there known effective ways to clear this problem? Obviously these wall plug DC PSUs are not the radio's original PSUs, but they are the cheaper OEM made or unknown makes.

author: geggi1
author_rank: Frequent Contributor
timestamp: March 18, 2023, 08:29:51 pm
content: Get a PSU with a transformer not a switcher and you are most likely good.

author: M0HZH
author_rank: Regular Contributor
timestamp: March 19, 2023, 09:07:00 am
content: You can experiment with choke ferrites on the power cable, but I'd recommend either a linear supply or at least a quality SMPS with proper filtering.

author: profdc9
author_rank: Frequent Contributor
timestamp: March 21, 2023, 03:05:53 am
content: On the radio I designed, I included a filter for the input DC voltage, also to prevent radiation of the local oscillator on the power cable.It consists of a conventional arrangement: two shunt capacitors and a common-mode choke between them. The two shunt capacitors are tied to separate grounds on each side of the choke.You could try something similar if you need to filter a noisy wallwart.

author: M0HZH
author_rank: Regular Contributor
timestamp: March 21, 2023, 09:09:25 am
content: Quote from: profdc9 on March 21, 2023, 03:05:53 amThat is a good step, unfortunately it won't stop EMI radiated by the power cable from the switcher to the input of the radio, which then gets picked up by the radio's antenna. A second choke at the switcher's output could help.

author: radiolistener
author_rank: Super Contributor
timestamp: March 21, 2023, 12:31:33 pm
content: Switching mode power supply is a very bad choice for receiver. Any radio receiver likes linear power supply.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: March 22, 2023, 04:22:52 am
content: Quote from: radiolistener on March 21, 2023, 12:31:33 pmNot true. I have a 13.8V 23A SMPS (Manson SPA8230G) which is extremely RF-quiet (very low EMI). Everyone in the amateur radio circles loves them.Cheap and nasty SMPS are obviously going to be EMI generators.

author: M0HZH
author_rank: Regular Contributor
timestamp: March 22, 2023, 12:07:33 pm
content: I can confirm, the Manson stuff (and all their rebrands) is good.
HP R11644A WR-28 cal kit - Page 1
Forum section: electronics / rf-microwave

author: 0culus
author_rank: Super Contributor
timestamp: April 01, 2023, 04:16:03 am
content: When surplus shopping the other day, I ended up with a partial R11644A TRL cal kit. Apparently what happened was, the prior owner won it at surplus auction, and it was complete. But, when he went to pick his items up, the precision termination, the parts for the offset short, and the floppy disk were gone. Really lame. So, I have three nice WR-28 line sections, the tools (hex screwdriver and a tiny open end wrench), and the hardware (except for the screws and nuts...the thief took those too) for cheap.I figure I could probably buy a complete one for what it would end up costing to make this kit whole again.Anyway, I don't have any microwave equipment in this band (yet...) but I figured it might be of some interesting to see some rather tiny waveguides.
Many tones into an LNA? - Page 1
Forum section: electronics / rf-microwave

author: rfengg
author_rank: Regular Contributor
timestamp: March 06, 2023, 05:04:51 pm
content: Could anyone advice if driving a wideband LNA with 2 tones of equal amplitude of -10dBm from a RF mixer , say at 10Ghz and 15Ghz, will reduce the output of the LNA compared to driving the LNA with a single tone say 10Ghz at -10dBm?I am facing this issue that when I drive a LNA with one tone @ 10Ghz and -10dBm, I get the expected output, but when 2 tones 10Ghz and 15Ghz are present at the LNA input , the output of the LNA is reduced at both tones.

author: mawyatt
author_rank: Super Contributor
timestamp: March 06, 2023, 07:00:02 pm
content: Likely LNA saturation, -10dBm is a large input level for an LNA.Best,

author: TimFox
author_rank: Super Contributor
timestamp: March 06, 2023, 07:23:47 pm
content: Note that on a power basis, two tones at -10 dBm each add up to a total power of -7 dBm, but the peak envelope power of each tone singly is -7 dBm and the peak envelope power of both together is -1 dBm.For independent waveforms, the (mean) powers add directly, but the peak amplitudes (voltage) add directly to give the peak power.The peak power (voltage) is what saturates the amplifier.

author: ejeffrey
author_rank: Super Contributor
timestamp: March 06, 2023, 10:36:02 pm
content: Your amplifier should have it's 1 dB compression point in its data sheet, which up to the beating concern raised by TimFox should basically tell you what you need to know.

author: Chat GPT
author_rank: Contributor
timestamp: March 10, 2023, 10:35:53 am
content: The presence of two tones at different frequencies can result in intermodulation distortion (IMD) products, which can fall within the frequency range of interest and interfere with the LNA's operation. This effect is more pronounced in wideband LNAs, which are designed to amplify a wide range of frequencies.When two tones of equal amplitude are present at the LNA input, they can mix in the LNA itself or in any other non-linear component in the signal chain, creating IMD products at frequencies that are the sum or difference of the original frequencies. In your case, the difference frequency would fall within the frequency range of the LNA, causing interference.To mitigate this effect, you can use a bandpass filter at the input of the LNA to remove any unwanted signals outside the frequency range of interest. You can also adjust the amplitude and frequency of the tones to avoid creating IMD products within the frequency range of the LNA.Another solution would be to use a mixer or frequency converter to downconvert the signals to a lower frequency before amplification, which would reduce the impact of IMD products.In terms of testing, it is important to ensure that the measurement setup is properly calibrated and that any unwanted signals or noise sources are properly controlled or shielded
Photodetector AC coupling - Page 1
Forum section: electronics / rf-microwave

author: Prisas
author_rank: Newbie
timestamp: March 08, 2023, 07:38:49 am
content: Hi everyone,i am using a photodetector, the output is 50 Ohm AC coupled, and I read this signal with a DAC, whose input is single ended 50 Ohm Ac coupled. When I look at my photodetector signal with an oscilloscope (200 Msps, in AC or DC mode 1 Mohm), the signal looks fine and the noise is about +-2 mV. But when I look at this same signal with my DAC, the noise is +-0.5V which is the maximum range of my DAC, and I dont understand why, for your information, the samping rate of my DAC is 5 GspsAny guesses ?

author: LM21
author_rank: Regular Contributor
timestamp: March 08, 2023, 09:36:21 pm
content: You probably use ADC, not DAC.
Any high-frequency (2.4-5Ghz) RF gurus/enthusiasts in Melbourne? - Page 1
Forum section: electronics / rf-microwave

author: seon
author_rank: Regular Contributor
timestamp: March 03, 2023, 05:43:59 am
content: Hey folks..Are there any "non HAM radio" Melbourne based groups or meetups etc for folks that work and play in the higher frequency RF realm - that also play in the small form factor electronics space?I'm looking for folks that have a experience wth both RF layout & design, impedance matching & harmonics filtering plus knowledge/experience going through certification (CE/FCC) on MCU based hardware.When I say "non HAM radio" - I don't mean to be rude or show any prejudice.. I have many friends that play in the HAM radio space, but none of them have experience in 2.4Ghz and above, and most can't even see the electronics I build without a zoom lens..... so I'm trying to find folks more specific to the type of things that I am doing.I'm asking about Melbourne based because it's nice to have real face to face meetings these days after so long without... but I'm also happy to know about online groups/forums of similar nature.Also, if there is a better place to post this, I'm happy to move it.PS: Also feel free to tell me how wrong I am about the HAM radio crowd - I can take it!Thanks very much,SeonUnexpected Maker

author: Guy_Ellis
author_rank: Contributor
timestamp: March 04, 2023, 10:41:14 pm
content: Hi Seon,At work I've put several products through CE, most with WiFi.I'm based in Melbourne too, drop me a line if you want to chat.Regards,- Guy.

author: LukeW
author_rank: Frequent Contributor
timestamp: March 06, 2023, 02:49:39 pm
content: The SDRMelbourne group might be worth checking out.
Low frequency noise figure of 3SK293 and similar dual gate FETs? - Page 1
Forum section: electronics / rf-microwave

author: rf-fil
author_rank: Regular Contributor
timestamp: March 12, 2023, 07:31:09 pm
content: As per title. Low frequency (below 200MHz) noise performance of these silicon FETs is not specified. Same for 3SK293 and BF998. Would anyone happen to have a source of this info? I know that GaAs devices can have a very high 1/f corner frequency, but I assume this won't be the case for these.(I'm ordering a noise source to do my own measurements but would prefer to save some effort...)

author: TimFox
author_rank: Super Contributor
timestamp: March 12, 2023, 10:16:00 pm
content: When I was involved in low-noise amplifier work between 5 and 100 MHz, I found that RF dual-gate MOSFETs had a higher "corner frequency" (where the excess or pink noise equaled the white noise) than did JFETs.One can measure and specify a noise figure below the corner frequency, but it doesn't look good on the data sheet when the designer needs lower frequencies.The only MOSFET in Appendix II of C D Motchenbacher and F C Fitchen,Low-Noise Electronic Design, Wiley 1973 is the 2N3631 (single-gate, originally Siliconix, N-channel).The input noise voltage density rises below 1 MHz: approximately 5 nV/Hz1/2at 1 MHz, rising to 100 nV/Hz1/2at 1 kHz (continues to rise to 10 Hz on the graph).By comparison, the 2N3821 JFET is about 5 nV/Hz1/2down to about 3 kHz, rising to 7 nV/Hz1/2at 60 Hz, then flat down to 10 Hz.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: March 13, 2023, 11:24:48 am
content: What are you attempting to use them in?

author: rf-fil
author_rank: Regular Contributor
timestamp: March 13, 2023, 07:14:41 pm
content: This is for a 21MHz IF low noise amp. I know they are being used for it already, but wanted to see how good they really are and if there is anything better out there. Also wondered if they'd make a good VCO.I answered my own quesiton now. This was in an article by Ulrich Rohde -https://www.microwavejournal.com/articles/38973-low-noise-tuning-diodes-for-voltage-controlled-oscillators:"Generally, fc varies with device type as follows: Si JFETs, 50 Hz and higher; microwave RF BJTs, 1 to 10 kHz (as above); MOSFETs, 10 to 100 kHz and GaAs FETs, 10 to 100 MHz."So, yes dual gate FETs are OK for anything from 100kHz to 1GHz. But they won't make a good VCO; only JFETs and BJTs will.
Yaesu VX-5R Antenna Stub - Page 1
Forum section: electronics / rf-microwave

author: metrologist
author_rank: Super Contributor
timestamp: February 20, 2023, 05:22:21 pm
content: I bought this tri-bander used and it did not come with the 6m antenna stub, so I was thinking of making one.I started with 56" of insulated wire connected to the threads at the tip of the base antenna (where the 6m or 2m/70cm stubs connect) and measured VSWR valley was a little below the target frequency. I wrapped that wire around a wood dowel and the VSWR valley was up around 100M.Not sure which direction to go now. Any ideas what magic they have in that stub?BTW, with the 2m/70cm stub, the VSWR measures 1.2:1 and 2.7:1, respectively. This is on an antenna analyzer with N-SMA adapter. I measured the Diamond SRH320A antenna and saw 4.4:1 and 1.1:1, respectively.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: February 21, 2023, 11:35:10 am
content: 1/4 wave of straight wire and 1/4 wave of coiled wire behave VERY differently. coiling the wire creates a loading effect, which lowers the resonance frequency. 100MHz will be one of the harmonics. extreme loading has probably given it such a narrow (high Q) fundamental resonance that you missed it.also don't forget that for a handheld, your hand grabbing it creates the other half of the antenna. so classical rules like "1/4 wavelength" might only get you into the ballpark.. it'll need plenty of adjustment. or you can add a tiger tail (?) which is a tuned counterpoise.

author: metrologist
author_rank: Super Contributor
timestamp: February 22, 2023, 04:25:37 pm
content: It could have been a mode. My antenna analyzer can sweep from 2MHz up, but I might have set it to sweep from 25MHz to 500MHz, and could have missed the primary. I'll do it again, if we have power tonight...

author: metrologist
author_rank: Super Contributor
timestamp: March 01, 2023, 10:43:36 am
content: Well, I tried all sorts of wrapping various wire lengths around a dowel as an extended antenna stub with various loading positions (continuous, top, center, bottom...). While I can get a return loss or VSWR dip in center band, it's too narrow and not quite low enough. The Smith chart will show almost zero reactance but with very high resistive impedance, so it wouldn't radiate much.Since it's an extra piece, might as well just build or buy a complete antenna for the 6m band.Here's an option: Diamond SRH-940 covers the three bands my HT covers.Or I could just go with, nothing's ever happening on 6m anyway.
Pronunciation of "Friis" - Page 1
Forum section: electronics / rf-microwave

author: pdenisowski
author_rank: Super Contributor
timestamp: February 28, 2023, 03:10:37 pm
content: I have always pronounced this like the English word "freeze," /friz/ but I've also heard it pronounced as "frees" /fris/ and even "frihs" /frɪs/I'm preparing a video where I talk about the Friis equation and want to see if I'm going to catch heat for pronouncing it the way I always do[Don't laugh: I've had people criticize the way I pronounce VSWR (viz-wahr) and NVIS (nih-vuhs) in previous videos]Thanks!(Edit: added IPA)

author: JohanH
author_rank: Frequent Contributor
timestamp: February 28, 2023, 03:18:45 pm
content: The name Friis is originally Danish. Correct pronunciation would be "frihs" or "frees" (vocal sound as in "beat"). I'm not a native English speaker so I wouldn't know the difference between "frees" and "frihs"; sounds the same to me. But definitely not "freeze", as the z-sound doesn't really exist in Danish.

author: JohanH
author_rank: Frequent Contributor
timestamp: February 28, 2023, 03:30:15 pm
content: And the R-sound should actually sound like a French R if we are picky. IPA spelling of "Friis" would be . In real Danish, the vocal (i) should be followed by "ˀ" (Stød), which is a form of glottal stop and btw. also impossible for me to pronounce as Swedish speaker. So I'm happily pronouncing "i" as a longer vocal there instead.

author: JohanH
author_rank: Frequent Contributor
timestamp: February 28, 2023, 03:33:10 pm
content: (The name comes of course originally from the Frisian Islands).

author: pdenisowski
author_rank: Super Contributor
timestamp: February 28, 2023, 04:10:58 pm
content: Quote from: JohanH on February 28, 2023, 03:30:15 pmA man who know his phonology and can figure out how to type IPAThanks!
Tube tester question - Page 1
Forum section: electronics / rf-microwave

author: Halwih
author_rank: Newbie
timestamp: February 27, 2023, 08:47:46 am
content: Hello,I am testing a few 6SJ6C tubes from an estate sale. They both test good but the meter pointer has a little flutter.I've seen this before but not sure if this is signs of a bad tube or what? Thanks

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: February 27, 2023, 04:07:42 pm
content: Hi Halwih,i guess the tube is oscillating.You can check with a shorted scope-probe (gnd-wire to hook/tip) sensing around the tube.If that's the case, connect the grid via a resistor (100 Ohm to 1k) or/and the anode via choke/inductivity (some yH).Since your tubes have an anode-cap the later one should be easy. :-))Good luck.

author: Stray Electron
author_rank: Super Contributor
timestamp: February 28, 2023, 02:10:25 am
content: Have you checked the caps in your tube tester? All of the ones in my old EICO TT were deader than hell when I bought it and that was 15+ years ago.