hybridfree/eevblog-posts huggingface dataset:
kenwood ts-850 pll unlock - Page 1
Forum section: electronics / rf-microwave

author: m3vuv
author_rank: Super Contributor
timestamp: October 12, 2019, 08:04:41 am
content: Hi all ive a kenwood ts-850s,when its been on an hour or more the pll goes out of lock,i dont know but i found tc5 ref oscillator cap very twitchy to set at 20mhz,could this cause the pll issue?,ive replaced the caps on the car boud about 3 months ago,it has the later dds chips in it,thanks in advance Paul m3vuv,73.

author: German_EE
author_rank: Super Contributor
timestamp: October 12, 2019, 08:35:54 am
content: OK, first, THANK YOU for doing the cap change because I've seen two TS-850 rigs where the PCBs were so badly corroded from capacitor juice that the rigs had to be scrapped.Now, to your problem. The TS850 has four VCOs which are switched in one at a time depending on which band you are using. If one or more of these VCOs are operating on the edge of the alignment window then you will see the symptoms that you describe. The cure is to open up the rig and do the PLL alignment detailed on page 98 of the service manual.The 30pF trimmer capacitor for the 20 MHz reference? Replace it. For the sake of your sanity measure the value of the old trimmer then fit a fixed capacitor plus a small value trimmer. For example, if you measure 12pF then fit a 10pF fixed capacitor and a 5pF trimmer.How do I know all of this? The service manuals for Kenwood rigs are very very good.

author: m3vuv
author_rank: Super Contributor
timestamp: October 15, 2019, 08:52:24 am
content: got it wrong,its tc1 faulty not tc 5 !!

author: m3vuv
author_rank: Super Contributor
timestamp: October 15, 2019, 01:27:50 pm
content: Well,i decided to spend some time on this today,going thru the alignment as per theservice manual,the tp voltage should of been 5v at 30MHZ,it was 3.6 v,got that right and set the 20mhz ref,recaped the display board and renewed the caps in the audio amp as well,its made a world of difference,its like listening to a new radio!,been on 2hrs now and the pll seems solid s a rock!.cheers m3vuv.

author: m3vuv
author_rank: Super Contributor
timestamp: October 16, 2019, 02:04:18 pm
content: Well,i thought i had this sorted,untill it started doing the pll unlock again,sure enough tc 1 was off againe,was getting 3v again at test point 2 on the pll(should be 5),i decided to replace c1 in the metal can on the pll,was pretty hard to do but it seems to go well,anyhow long story short,i now have 0.1 volts on tp 1,its as iff the whole board is dead!,checked all cables etc,cant see anything wrong,also the 20mhz ref oscillator isnt going,any ideas folks?

author: m3vuv
author_rank: Super Contributor
timestamp: October 18, 2019, 07:01:50 am
content: sorted,was a bad vreg 78 series ic,on the car board,changed and all now good and stable,been on all night and hasnt gone out of lock once!.

author: German_EE
author_rank: Super Contributor
timestamp: October 18, 2019, 07:43:34 am
content: Another possible fault cause to add to my notebook, thanks for the update and I'm glad that you finally got it working. It looks like Dave's advice still holds true, check power supply voltages first.
Inside a SMA connector - Page 1
Forum section: electronics / rf-microwave

author: jmw
author_rank: Frequent Contributor
timestamp: October 28, 2019, 07:37:23 pm
content: I (sloppily) cross-sectioned a SMA PCB connector a found a couple of interesting things (click for full size):1) In the lengthwise center, the insulation diameter steps up and back down. The center pin also has a ring-like feature at the same position. What's this for and what does it do to the connector's performance? Possibly mechanical retention, but it must have some effect on the s-parameters.2) The insulation diameter, from manufacturer CAD models, is a little smaller than it should be to obtain 50 ohm impedance. The CAD model has it at 3.91 mm, whereas the coax impedance formula requires 4.26 mm at PTFE's \$\epsilon_r\$ of 2.1. In fact, MIL-STD-348 doesn't give a dimension for the dielectric. I guess this means you do what you need to meet your VSWR spec. Are the features in the center some kind of compensation to do that?

author: radiolistener
author_rank: Super Contributor
timestamp: October 28, 2019, 08:05:12 pm
content: Quote from: jmw on October 28, 2019, 07:37:23 pmyes, these Chinese connectors have bad performance at GHz frequecy. But if you're using it below 500 MHz for 100W power or less, they works good enough.

author: jmw
author_rank: Frequent Contributor
timestamp: October 28, 2019, 08:08:48 pm
content: It's a Molex connector 73251-1350 bought through a US supplier, not Chinesium.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 28, 2019, 08:27:14 pm
content: Quote from: jmw on October 28, 2019, 08:08:48 pmThat's not a connector from which I would expect good RF performance. The datasheet does not even specify VSWR or insertion loss. It does say 18 GHz, but what does that mean? Surely, a signal will go through it somehow at 18 GHz.It's low cost and has its purpose, but it's not made for precision at GHz frequencies.

author: jmw
author_rank: Frequent Contributor
timestamp: October 28, 2019, 10:26:33 pm
content: Good point. I can pay a little more to dissect the Rosenberger 32K10A-40ML5 which is almost identical from the outside. Let's see if Rosenberger will send me a CAD model too ...

author: jmw
author_rank: Frequent Contributor
timestamp: October 31, 2019, 10:11:03 pm
content: For fun, here's the cross section of the Rosenberger connector. The dielectric is more uniform in diameter and looks like it is being held in with 4 dimples made on the barrel. The pin is knurled which probably also makes for some irregular impedance but it must be a small effect below 8 GHz given the datasheet VSWR of 1.05 + .005 * f/GHz.

author: scatha
author_rank: Regular Contributor
timestamp: November 01, 2019, 08:53:38 am
content: There's surprisingly little going on in even that high-end SMA connector. For comparison this is the cross-section of a (presumably high-end) TNC connector I have that is mounted in epoxy. It really is a thing of beauty.
Fourier Series of a bipolar square wave - Page 1
Forum section: electronics / rf-microwave

author: Ralphy007
author_rank: Contributor
timestamp: October 11, 2019, 10:07:49 am
content: Hi, I am trying to calculate the Fourier Series for a bipolar square wave which is formed by taking 4 samples of a sinewave. Please see the attachment.I know a0 is zero just by looking at the waveform, but I am having difficulty with a1.I believe a1, should also be zero, but as you can see from my derivation I am not getting zero and I am pulling my hair out wondering what I am doing wrong. Any help would be more than welcome.

author: Andy Watson
author_rank: Super Contributor
timestamp: October 11, 2019, 12:11:37 pm
content: Quote from: Ralphy007 on October 11, 2019, 10:07:49 amAgreed, it's a symmetrical waveform with zero DC content.QuoteWhy?a1 represents the amplitude of your fundamental frequency \$\frac{1}{T}\$ - I wouldn't expect it to be zero.Edit: To clarify - Looking at the waveform it should obviously have some fundamental frequency in there, but it also has some phase offset. So neither \$A_1\$ or \$B_1\$ will be zero.

author: Ralphy007
author_rank: Contributor
timestamp: October 11, 2019, 03:12:00 pm
content: I am pretty sure I reaqd somewhere a1 should be zero, but believe me joy o joy if it is not.I will calculate a value for b1 and see if a can find the correct overall Fourier Series.
I want a N2PK VNA - Page 1
Forum section: electronics / rf-microwave

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 11, 2019, 09:40:32 am
content: Dearhow should I buy a N2PK VNA? I checked they put the schematic and BOM and PCBs and enclosure. but I need a setup like the below not as a separate kits and ... (this is bcoz I can not order the components from many distributors, I'm not lazy but I have a problem! believe me , I can montage all of them but at-least I want all the components and kits together)http://www.makarov.ca/vna.htmThanks
RF Power and Inductor RMS Current - Page 1
Forum section: electronics / rf-microwave

author: josefmtd
author_rank: Contributor
timestamp: October 10, 2019, 03:31:40 am
content: Hello all,I have a question when designing an LC filter with inductors made by e.g. Coilcraft, there is an RMS current in the datasheet, and I wonder how this relates to how much RF power the system can handle.Can I still use the I^2 R with the R being the characteristic load of the RF line (50 ohm), so would I be able to get the maximum power handling of an inductor as:P = I(rms)^2 * 50 ohm?

author: josefmtd
author_rank: Contributor
timestamp: October 11, 2019, 07:24:36 am
content: Did a little digging and stumbled uponhttps://media.tecnoimprese.it/Coilcraft_BoD_RevisedV3.pdf, it says that the Irms current is the current that leads to 40 degree Celsius temperature increase. I guess it does not help with the RF power calculation.My Google-fu isn't helping and I cannot find a reference to calculate for maximum power handling anywhere, does anyone have any pointer or clues?
California declares VHF/UHF repeaters obsolete - Page 1
Forum section: electronics / rf-microwave

author: tocsa120ls
author_rank: Regular Contributor
timestamp: October 11, 2019, 07:06:18 pm
content: I'm sure the person that drafted this never used anything but his/hers/xir car radio.https://offgridsurvival.com/california-officials-declare-ham-radio-no-longer-a-benefit/

author: Lord of nothing
author_rank: Super Contributor
timestamp: October 27, 2019, 04:22:17 pm
content: QuoteSo where is the Problem?!Put them on Private Land...Here in Austria its quite the same. The are mostly on private Property.On some Mountain the share the Station with other Commercial Services to save cost.
Fm Radio Reception - Page 1
Forum section: electronics / rf-microwave

author: nvidia
author_rank: Regular Contributor
timestamp: October 09, 2019, 01:16:08 am
content: is this the best way to get better Reception or is there a cheaper way

author: xrunner
author_rank: Super Contributor
timestamp: October 09, 2019, 01:19:53 am
content: Quote from: nvidia on October 09, 2019, 01:16:08 am"best" and "cheaper" do not go together.The best way is to put up an outside antenna and run a coax to your receiver.

author: Shock
author_rank: Super Contributor
timestamp: October 09, 2019, 05:02:31 am
content: You can make an indoor antenna as well for a few bucks look up FM dipoles and folded dipoles. It really depends on you're situation, how far you're away from the transmitter, what radio, what antenna you are currently using.
Fun with ring modulators for inverted SSB and crazy audio (video) - Page 1
Forum section: electronics / rf-microwave

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: October 09, 2019, 03:15:18 am
content: If you've never played around with a ring modulator I recommend you do so.I used it to invert an SSB signal. That allows you to hear LSB signals on a receiver that only does USB.Other applications include voice scrambling and electronic sound effects.A ring modulator just needs two audio transformers plus four diodes.And an audio signal generator.More here!
Is it possible to inject audio on a TV antenna coax? - Page 1
Forum section: electronics / rf-microwave

author: Chris Wilson
author_rank: Super Contributor
timestamp: October 03, 2019, 12:20:13 pm
content: Is it possible to feed audio, like you can DC, into a terrestrial TV antenna coax whilst retaining its function for UHF TV reception as you inject and remove DC on antenna feeds? Thanks.

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 03, 2019, 12:51:52 pm
content: Sure, and with the same approach as for DC: you can couple the audio into and out of the coax with a series inductance that has very low parasitic (parallel) capacitance (ie - as few turns as possible, and preferably with a core that is lossy at UHF). The inductance will present a high impedance to the UHF signal while presenting a minimal impedance to the audio signal, and even a few hundred nH will be more than sufficient here.

author: tkamiya
author_rank: Super Contributor
timestamp: October 08, 2019, 08:56:32 pm
content: I've only read about this and don't have a first hand experience.But according to later version of ARRL ham radio handbook, it states using coaxial cable or terminating audio output with capacitors are bad ideas because it can throw some amplifiers into oscillation. lf you feed audio into coax, from amp's prospective, it will look like huge C across terminals and L in series. This is mentioned in RFI prevention section of the handbook. I don't have one handy to mention exact phrase or page number.
News story about VK5ZAI. ABC Australia  - Page 1
Forum section: electronics / rf-microwave

author: wilfred
author_rank: Super Contributor
timestamp: October 06, 2019, 07:14:03 am
content: https://www.abc.net.au/news/2019-10-06/nasa-considers-amateur-radio-buff-part-of-astronaut-family/11530046I saw it today and thought It might interest some Hams here.
315MHz RF Receiver Troubleshooting - Page 1
Forum section: electronics / rf-microwave

author: Rofflesaur
author_rank: Contributor
timestamp: October 02, 2019, 11:25:36 pm
content: I have a RF receiver from a Volkswagen key-less entry system (circa 1997). The receiver is part of the alarm module, and contains relays for the horn honk and light flash, as well as starter bypass. Everything on the board functions as it should, however the range for the key fob transmitters is literally about 1-2" from the PCB. I did replace the battery, as well as purchase a new transmitter with fresh battery. The transmitters both pair and function, but at an extremely short range. I repair PCBs daily, but RF is completely out of my area of expertise. All the components on the board look okay too. I've done some research and found a ton of info for troubleshooting for poor transmitter performance, but what exactly would make a receiver perform poorly? The antenna connections to the board are solid, and I even resoldered to be sure. I tried winding that variable inductor in and out a couple turns in each direction and it also had no affect. I'm not sure where I should begin to look.Here's pics of both sides of the board:Thanks.

author: radiogeek381
author_rank: Regular Contributor
timestamp: October 03, 2019, 12:31:17 am
content: Is Q1 cracked or otherwise damaged? I can't tell from the pic if that mark is a crack, or just a mark.In any case, there will be an RF amplifier somewhere in there. It may be discrete (like Q1 maybe) or it might just be a component on one of the multi-pin chips...

author: floobydust
author_rank: Super Contributor
timestamp: October 03, 2019, 01:00:53 am
content: Check for cracked solder joints on the RX antenna and U1 pin 1 needs more solder.Otherwise I would try re-tune the receiver. It looks like a typical ASK detector so U1 might be the RX op-amp.When the unit is powered up, the RF oscillator radiates strongly nearby, I have used that to tune them with a sensitive freq. counter or SDR and probe nearby.Without that equipment, note where L1's slug is and give it 1/4 to 1/2 turn in a lucky direction and see if range improves.
A Possible Solution to GPS Reception Problems - Opinions Please - Page 1
Forum section: electronics / rf-microwave

author: German_EE
author_rank: Super Contributor
timestamp: October 14, 2019, 06:56:38 pm
content: Like many I have poor GPS reception due to a poor location and an inability to mount the antenna in a better spot. I therefore have the following idea.1) I use four of the small puck antennas rather than one, all of them mounted on a ground plane more than a quarter of a wavelength apart.2) Each of the puck antennas are connected to a bias-t at the SMA end with the inductor going to a common 3.3V low noise supply and the capacitor connected to a four input combiner.3) The output of the combiner is connected to the GPS receiver.This will not be cheap as I am working at 1.5 GHz here so I would appreciate some opinions before heading for Minicircuits.

author: Ian.M
author_rank: Super Contributor
timestamp: October 14, 2019, 08:11:12 pm
content: Any satellite in a direction where there's an odd number of half-waves difference in the path length between two of the antennae will have their contribution to the received signal cancel out. There will be more complex nulls formed by the interaction between pairs of each possible pair of antennae as well. Due to the number of satellites required for a fix, the odds are that the improvement in reception from the higher gain directions where the signals are in phase wont actually give you a more reliable fix because as they move, it will keep loosing ones that were at a good signal level into a null.

author: Dek
author_rank: Regular Contributor
timestamp: October 15, 2019, 07:55:41 pm
content: A home built Quadrifilar Helix Antenna would make a good project.Dek.

author: Gribo
author_rank: Frequent Contributor
timestamp: October 16, 2019, 06:13:56 pm
content: Do you have access to the roof? If so, a repeater is the easiest and cheapest solution. Take into account that it will give you the roof's coordinates.

author: Berni
author_rank: Super Contributor
timestamp: October 16, 2019, 06:26:12 pm
content: No you can't combine multiple antennas like this because the signals are coming from various directions depending on where the satellite is. So if its directly above all antennas recieve the signal in phase, if its 45 degrees you get half the distance between them out of phase and if its at 90 then you get one whole distance out of phase.As mentioned by Dek a Quadrifilar Helix design is nice for GPS due to the signals rotational polarization. Ground planes do help patch antenna designs a lot. The professional high precision GPS antennas also tend to feature multi path suppression rings around the antenna to improve signal quality(especially the phase information). These are basically just vertical cylinders around the antenna that capture signals coming in at shallow angles.You can buy antennas like this in the form of GPS survey antennas that are in the shape of large >15cm diameter discs or domes, might want to look on the used market for one as new ones can quickly cost over a grand.
HP8753C/D option installation guide - Page 1
Forum section: electronics / rf-microwave

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: October 03, 2019, 04:16:32 pm
content: Update:Found it. Basically works the same for the c/d as for the later models. Just follow the guide below.Only jumper is different. It is a 2.54mm pinheader (the only one) with a jumper. Normaly the jumper is to one side, marked "NORM", move that jumper to the other side "ALTE".HiIs there sombody who's tried that?I went with Kirkby's idea to add option 002/010 to my 8753D:https://www.kirkbymicrowave.co.uk/Everything-you-wanted-to-know-about-the-HP-8753-VNA/And I got the paswords, yayHowever, searching for an upgrade guide like this:https://xdevs.com/doc/HP_Agilent_Keysight/8753ES_8753ET/8753ES_Option_010_TDR_Upgrade_Kit_Installation_Note.pdfyelded no results. Nothing in the sm as wellApparently it was the same for the c/d version but certainly different on the e/es etc. versions since they have another firmware and cpu board.
MC1496 or NJM2594? - Page 1
Forum section: electronics / rf-microwave

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 15, 2019, 09:08:58 am
content: Helloin a circuit they used a MC1496 or NJM2594. there are two signals at the inputs which one is Carrier and another is a Signal and both are single ended.there are two ways to detect the signals:which one is better?as you see both Signal and Carrier are Single Ended if we use MC1496 we should use a Balun to translate them to a differential signal but in the second approach we don't need the Baluns at all but which one is better? for example the first solution can eliminate even harmonics and I think the measurement would be smoother.plus I want to replace MC1496, is there any equivalent for this Modulator IC?Thanks

author: wraper
author_rank: Unknown
timestamp: October 15, 2019, 09:25:44 am
content: MC1496 and NJM1496 is the same IC. Using Balun or not is in not dependent on which of these 2 ICs you use.

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 15, 2019, 09:33:59 am
content: Quote from: wraper on October 15, 2019, 09:25:44 amI'm sorry I edited the second pic. MC1496 and NJM2594
Sanity check for LF-VLF Loop Antenna idea... - Page 1
Forum section: electronics / rf-microwave

author: Co6aka
author_rank: Unknown
timestamp: October 02, 2019, 05:38:05 pm
content: Maybe I'm off, or on, my RX ("meds") so just in case a sanity check please...I'm thinking about testing a galvanically isolated unshielded RX loop for LF-VLF. My wild idea is to pass the loop through a 500kHz BW current transducer and then impedance match the transducer to a low noise JFET amplifier. I have 10-foot diameter frame from long-past experiments with tuned loops to mess with. I haven't actually tried the current transducer idea yet; I'm wondering if anyone has, or what any thoughts might be. Thanks!

author: radiolistener
author_rank: Super Contributor
timestamp: October 02, 2019, 06:36:53 pm
content: could you please draw the picture what you're talking about? Is it magnetic loop with transformer coupling followed by LNA?

author: Co6aka
author_rank: Unknown
timestamp: October 02, 2019, 10:59:45 pm
content: Basically just a 10-foot diameter circular conductor running through the aperture of a AC current transducer, with the transducer matched to a JFET LNA.I'm looking for my current transducer which, if merember correctly, is spec'd "30Hz to 500kHz" or something like that. I don't recall the "sensitivity" ratio though. Actually, I don't want to hear stuff much below 10kHz, so rolling my own transducer with a more appropriate core and ratio might make more sense.
RF SMD component ID help - Page 1
Forum section: electronics / rf-microwave

author: NikkiC
author_rank: Contributor
timestamp: September 29, 2019, 08:22:35 pm
content: Have what looks like a couple of GasFETS that I could use some help on identifying. These are from an SAT dish LNR PCB. I'd really like to figure out how to utilize these in a possible project. Part of the thrill I get out of building things comes from building them from parts I have in the junkbox. This includes stuff like this. I'm hoping there is someone who has already been there and done that with these. If nothing else, get an idea as to which pin is GDS would be helpful. Anyone? Attached are PNG's of the two devices.TIA,Nikki
simple RF calibration/checkout tool sought  - Page 1
Forum section: electronics / rf-microwave

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: September 28, 2019, 12:28:18 am
content: I need to provide my mast-monkeys and site surveyors with a very simple tool to check on the function of a portable spectrum analyzer. Given a device setting, it needs to produce a well defined screen picture if used. Besides that, it must have a activation switch, function/battery indicator and (preferably) an N-type quick shove-on connector.And above all, it needs to be monkey proof. this precludes anything with open connections, such as a Minicircuits whatsit with wires. Frequency of interest is somewhere around 1GHz.Anyone seen something akin to it?

author: xrunner
author_rank: Super Contributor
timestamp: September 28, 2019, 12:53:14 am
content: What do you want them to see on the screen of the SpecAn? Like the same single-tone modulated FM signal (or AM) signal every time (or some other display)?I guess the power can be pretty low since it can just be directly connected.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: September 28, 2019, 01:07:58 am
content: Yes, the screen should show the same signal every time. Although it would be better if it could be coupled via a small auxiliary antenna too, as the site survey config does its measurements using an antenna.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 30, 2019, 02:37:11 pm
content: http://www.appliedemtech.com/usbsmain.htmlI have one of these:http://www.hsmicrowave.com/CMG.htmlSimple matter to mount the above in a box with a N connector, attenuator, PP3 battery and Led as needed.-------------------http://www.schwarzbeck.de/en/reference-radiators.html----------------------------------Steve

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: October 01, 2019, 11:00:36 pm
content: Thanks - thats it. I forgot about HSM, had found them once. Case closed.
Hallicrafters S53A repair - Page 1
Forum section: electronics / rf-microwave

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 24, 2019, 12:50:31 am
content: In this video I start a repair on an old Hallicrafters shortwave receiver from the early 1950's.Main failure was the 455Kc IF transformers. The dreaded silver mica disease.After 3 hours of repair I trimmed the video to 1.5 hours.Interesting what you find in these old radios.EDIT, forgot to hit post

author: xrunner
author_rank: Super Contributor
timestamp: September 24, 2019, 12:52:31 am
content: Cool will watch later tonight.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 24, 2019, 11:58:41 pm
content: Thanks, hope you get something from it.

author: German_EE
author_rank: Super Contributor
timestamp: September 26, 2019, 06:14:42 pm
content: Remarkable how that gunk comes off the chassis when you use the right solvent. I love this old stuff, especially when most of your pieces were made before I was born.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: September 28, 2019, 07:09:34 pm
content: Quote from: German_EE on September 26, 2019, 06:14:42 pmYep, right stuff takes it off. I use WD40 to clean most chassis. Stuff works great. A lot of the stuff I work on is older than myself.
2.4ghz antenna design - Page 1
Forum section: electronics / rf-microwave

author: jpwm
author_rank: Newbie
timestamp: September 21, 2019, 04:04:06 pm
content: Hi,I am currently designing a board which includes an ESP32, so I also need to add an antenna to make use of the WiFi and Bluetooth capabilities. I want to add a pcb antenna and have read through some application notes from various companies on how to do it, but I still can't resolve one question.A different pcb stacking, different FR4 material, plastic housing and practically everything will influence the resonant frequency of my antenna. In this application note TIhttp://www.ti.com/lit/an/swra117d/swra117d.pdfstates that this can be solved by making the antenna (in this case an inverted F antenna, the type I am planning to use) slightly shorter/or longer. But which part of the antenna ( i added the picture from TI) should be shortened or extended? Only L1 or every part (essentially scaling the whole antenna), or something different?It would be great if someone can answer this question and I don't have to try a dozen designs to find out.

author: awallin
author_rank: Frequent Contributor
timestamp: September 22, 2019, 03:37:23 pm
content: FWIW this reference seems to scale all (?) dimensions for two different PCB thicknesses:https://www.silabs.com/documents/public/application-notes/an1088-designing-with-pcb-antenna.pdfwithout real-world measurements and a simulation that matches the real-world this is going to be a hard thing to get right on the first try...

author: mayor
author_rank: Regular Contributor
timestamp: September 26, 2019, 09:09:08 am
content: I have implemented this antenna in a Bluetooth project. As you say, the environment has a huge impact on the match, and other TI app notes suggest using a Pi network rather than changing the length of the antenna.Do you have access to a VNA?

author: jpwm
author_rank: Newbie
timestamp: September 26, 2019, 09:43:17 am
content: I also implemented a pi-matching network for impedance matching, but still the resonanz frequency of the antenna should match the frequency that are used for wifi. I have a spectrum analyzer and a swr bridge available (though only very cheap ones). I will use a mathematic approach to calculate the actual impedance of my antenna (I found a detailed desciption here:https://mightydevices.com/index.php/2019/08/complex-impedance-matching-using-scalar-measurements-math-and-resistors/). In the coming month I might have the chance to use a vna in a university lab, but that lab is rebuild at the moment, so I don't want to depend on it.I will share my results when I have some;)

author: mayor
author_rank: Regular Contributor
timestamp: September 27, 2019, 09:34:25 am
content: Hi, check out this app note:http://www.ti.com/lit/an/swra227e/swra227e.pdfIt's a different antenna, but it may give insight as to length adjustments for your own.
Australian amateur licence conditions liberalised - Page 1
Forum section: electronics / rf-microwave

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: September 25, 2019, 11:46:33 am
content: Changes to the Australian amateur licence conditions released today have increased scope for construction and experimentation.Foundation licensees are the biggest winners, with the requirement to use commercially-made transceivers scrapped. They can also use computer controlled and digital modes.Also all hams can transmit wider bandwidth modes, enabling more experimentation with data modes.However the changes don't grant the extra transmit power and frequency allocations that some were hoping for.Summary video here:

author: mark03
author_rank: Frequent Contributor
timestamp: September 25, 2019, 04:52:37 pm
content: The replacement of specific bandwidth and mode restrictions with a blanket power-density limit (1 W / 100 kHz) is very interesting. I am wondering if there are other jurisdictions with similar rules, or is Australia the first?There are some potentially interesting things one could do with spread-spectrum modes on HF. Narrow-band is intrinsically less efficient due to frequency-selective fading, but that can go away with sufficient bandwidth. It depends on conditions, obviously, but off the top of my head I think something like 100 kHz is usually enough to get into the regime of uncorrelated fading across your signal.For those unfamiliar, imagine something like OFDM with coding across frequency, i.e. over the tones/carriers. With enough bandwidth, there will be roughly half of the carriers at above-average SNR while the other half are in a fade. This improves power efficiency vs. narrow-band modes like WSPR where the only option is to code across time.
Help characterizing my MCL 20db attenuator using my CMU200 - Page 1
Forum section: electronics / rf-microwave

author: sab
author_rank: Contributor
timestamp: September 23, 2019, 08:37:36 pm
content: I was trying to see how well my MCL 20db attenuator (specified to 2Ghz) worked and used FreRes with my CMU200. I stumbled upon several things.First, the output of my CMU200 isn't very stable between 500Mhz and 2.1Ghz. It varies by about -2.5db.Next, the attenuator does something bizarre. It is almost as if there are resonances at regular intervals. BTW, I tried with other attenuators and received similar looking results.Any advice would be much appreciated.

author: TheSteve
author_rank: Unknown
timestamp: September 24, 2019, 01:10:25 am
content: Does the CMU200 have a "normalize" option?Have you verified your cable/connectors are good?

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: September 24, 2019, 10:55:06 am
content: Resonances like that at regular intervals are typical of reflections. Sometimes they are there on purpose (filters/matching), sometimes they are parasitics.This is actually something you can also observe in some (lower cost) coaxial cables where the shield is wrapped as a ring of foil. The regular intervals where this foil overlaps always causes a tiny reflection, but over long lengths of cable this adds up.This is also why it is important to accurately measure (With lots of frequency points) when you use something past its rating - in this case the notches are quite wide, but sometimes they are very narrow, and if you use too few points you can easily miss it (and then be very confused as the results when using the component are all over the place).Could be that the cable you are using or the attenuator itself are showing this effect.My first guess would be poorly torqued connectors somewhere, then cable, but in this case, as the level is also a bit strange - I think it could be the output of the CMU itself. As the level is not stable, it suggests something is broken in there causing the ALC to fail. This same component might add missmatch.What you can do is just add bit of cable between attenuator and the CMU output. You should see the gaps between notches shift by a similar amount as twice the electrical length of that cable.

author: sab
author_rank: Contributor
timestamp: September 25, 2019, 03:36:38 pm
content: The CMU 200 doesn't have a normalize option, sadly.My cables are the generic cheap ones from ebay. I didn't suspect them but I will dig in.Thanks,Sanjay

author: sab
author_rank: Contributor
timestamp: September 25, 2019, 03:39:47 pm
content: I'm not sure I have the expertise to inspect the ALC, but I'll (i) do the cable experiment you suggest with an additional length of cable and (ii) plot more points.Thank you,Sanjay
PE43702 digital attenuators on ebay - Page 1
Forum section: electronics / rf-microwave

author: rhb
author_rank: Super Contributor
timestamp: September 23, 2019, 10:56:25 pm
content: I got some to play with. The first pair had a "grey shift" OLED screen with a large chip missing and a bad PE43702 board. The chip was *not* in the bag. So someone packaged known bad parts. The other one was fine. This model does not have a shield and uses the serial interface.I got two more with shields and configured for the parallel interface. However, other than by flipping the DIP switches under the shield they cannot be adjusted. None of the header pins on JP1 are connected to the D0-D7 lines on the PE43702. The DIP switches ground D0-D7. So the logical interface for the parallel mode is to ground the desired steps. But someone failed to connect the JP1 pins.One of the units would not select a -2 dB step using the DIP switches whereas the other did.As a test I rejumpered the one that would not select -2 dB to the serial interface and lo and behold it works.The response it not very flat above 2 GHz, but might be acceptable with calibration and MCU control.The one that came jumpered for serial use also doesn't have the JP1 pins connected to D0-D7. So don't plan on getting one of these and using toggle switches to set values unless you're willing to rewire the DIP switch. The serial UI board is configured to set values which the board won't do. But does do the ones that exist when you set them.I thought it curious that I couldn't find much mention of these. I think I might have found out why.Have Fun!Reg

author: radiolistener
author_rank: Super Contributor
timestamp: September 24, 2019, 06:13:20 pm
content: I think this is a crap with high noise. It's better to buy SMA attenuator kit for the same price.

author: rhb
author_rank: Super Contributor
timestamp: September 24, 2019, 07:04:51 pm
content: Quote from: radiolistener on September 24, 2019, 06:13:20 pmDo you *know* anything about them? Dismissive opinions are neither interesting nor useful.I have lots of attenuators, both SMA and N. Mostly fixed, but also some good quality adjustable units.I bought these to have some which could be controlled by an MCU for automating an annual full bench calibration system.I started the thread because I did not find any discussion of these. I thought that rather odd. Peregrine lists these as obsolete, so these are either old stock or counterfeits made by a Chinese fab house hired to make them who then stole the design.I've swept these from 1 MHz to 2.9 GHz with an 8560A w/ TG and they are quite good below 1 GHz. They ring a bit above that, but I suspect that is the PCB and SMA connectors, not the Peregrine 43702.I'll submit them to the tender mercies of my Tek 11801 & SD-24 when I get time. That will identify the source of the ringing. But the SMA footprints on the PCB are the leading candidates. The ground vias appear to be randomly sprinkled in sections of the board which suggests less than skillful board design.But at the moment, I have lots of paper work to sort and file.Have Fun!Reg
Telefunken "the rainbow" E127/kW5 - Page 1
Forum section: electronics / rf-microwave

author: Martin.M
author_rank: Frequent Contributor
timestamp: September 09, 2019, 05:13:39 pm
content: Boatanchor restoration,this is the Telefunken E127/kW5.A portable radio (it have 2 handles), around 44kg.Shortwaves Receiver, single conversion super, 8 tubes, revolver selection.This radio can listen AM, CW and sidebands by using it`s BFO.Filters: there is a adjustable crystal filter in the IF providing 4 bandwiths.BFO: ±3kHzTubes: all SQ types, mostly EF805sElectrolytics: not one ! all MPTuning: Geartrain with push for coarse (1:1) and pull for fine (20:1)scaling: 5 bands rainbow with a lot of light.The IF of 525kHz is the same then the second IF from the E108 VLF radio and the E104 SW radio, so it can use the same additional equipments like sideband selector, RTTY interface and so on.Case: steel made.Color:As E127/kW5 grey, used by the governement and the navy,nato green used by the army.It have a little loudspeaker and a holder for papers.civil version (E127/kW4, rare) is also grey, the different to the kW5 is: kW5 have all plugs on the front plate, kW4 have that at the backside only.You see here the grey kW5.first picture: it`s the right side up, "the rainbow"is the most cute boatanchor from Telefunken.

author: InductorbackEMF
author_rank: Regular Contributor
timestamp: September 22, 2019, 03:12:37 am
content: Hello martin!Just wanted to say thanks for all the great pictures/videos of all of gear you got!You are a amazing fellow and great "Doctor" for all valve/vintage gear.Ps Do not hurt your back lifting them things!Alex.
Deriving equations for coupled line transmission line for even-odd modes - Page 1
Forum section: electronics / rf-microwave

author: promach
author_rank: Frequent Contributor
timestamp: September 20, 2019, 11:23:00 am
content: Is V2e = V1e ， V2o = V1o ？If not, how would we arrive at equations relating {V2e, V2o} to {V1e, V1o} respectively ?
sharing UHF TV antenna for data reception - Page 1
Forum section: electronics / rf-microwave

author: Avi
author_rank: Contributor
timestamp: September 19, 2019, 11:59:43 am
content: I'm looking for a way to split a 75 ohm TV antenna connection (belling lee male) to both a 75 ohm TV (belling lee female) and a 50 ohm 915MHz data transceiver (SMA female).Any ideas/suggestions?

author: Gyro
author_rank: Super Contributor
timestamp: September 19, 2019, 07:06:23 pm
content: transceivermight be the key word here. What are the chances that you are going to overload the AGC in the TV tuner (presumably UHF band?) and cause breakup?

author: james_s
author_rank: Super Contributor
timestamp: September 19, 2019, 08:10:09 pm
content: If it's a transceiver you'll probably need a relay to disconnect the path to the TV whenever transmitting is taking place. 75 ohm cable and antenna is far from optimal for a transmitter expecting 50 ohm too.

author: donmr
author_rank: Regular Contributor
timestamp: September 19, 2019, 08:45:36 pm
content: If the data transceiver operates on a narrow channel then you could use filtering to split/combine the signals. Lookup how VHF/UHF repeaters are built.

author: Avi
author_rank: Contributor
timestamp: September 20, 2019, 02:14:18 am
content: I should point out, it is just in listening mode all the time, no trnasmitting. Im just looking for some sort of solution to match all the impedances and without a lot of loss (as resistors would do)

author: james_s
author_rank: Super Contributor
timestamp: September 20, 2019, 02:56:07 am
content: Any form of passive splitter is going to be -3db for each of the two outputs. Just get a splitter designed for TV antenna splitting, they are readily available off the shelf. If you don't want loss you can get an active splitter that contains an amplifier but they have disadvantages of their own.
BFR99 LTspice data - Page 1
Forum section: electronics / rf-microwave

author: ermeneuta
author_rank: Newbie
timestamp: September 12, 2019, 01:18:44 pm
content: Good afternoon all,I am in need of the LTspice data of the BFR99 PNP RF transistor. It looks interesting, 2 GHz ft, and low noise.I bought a few at an ham fair, and would like to simulate a couple of circuits before melting solder...Any takers ? Thanks in advance.Alberto

author: aurelZ
author_rank: Contributor
timestamp: September 16, 2019, 05:16:47 pm
content: Wellwhen i see BFR i was thinking that is plastic case transistor but i was wrong.according to all data sheet it is metal case UHF transistor Vmax 25V which lead me tothink that is some sort of BFY90 but little bit modern version.so it can be used like VHF-UHF common base amplifier on high freqs also as osc/mixer .
field strength measurement at LF? - Page 1
Forum section: electronics / rf-microwave

author: awallin
author_rank: Frequent Contributor
timestamp: September 14, 2019, 11:38:20 am
content: are there good DIY ways to measure radiated field strengt from an LF transmitter (100kHz or so), with reasonably accurate calibration so that the result in dBuV/m is good to preferably <<3 dB?I would probably need a mobile setup to map out the field strength by driving further away from the transmitter.ideas?DIY magnetic loop, with measured area and number of turns, followed by amplifier with known gain?DIY calibration of a mini-whip antenna - can this be done by driving a reasonably-sized (1m square) plate-capacitor with a known voltage and placing the mini whip mid-way between the plates??thanks for ideas/product-suggestions,AW

author: chris_leyson
author_rank: Super Contributor
timestamp: September 14, 2019, 12:10:19 pm
content: From the Radio Laboratory Handbook

author: radiolistener
author_rank: Super Contributor
timestamp: September 14, 2019, 05:52:38 pm
content: you're needs to measure it at least half wavelength away from transmitter antenna. It means that for 100 kHz you're needs to measure it at least 1500 meters away from antenna. Otherwise your measurement will be incorrect due to near field influence.You can use SDR receiver to measure relative transmitter power level. If you want to know absolute power level, you're needs to calibrate. With different antennas you will get different results, so you're needs to calibrate it with the same antenna which will be used for measurement.
Simple AsubL calculation, am I getting it wrong? - Page 1
Forum section: electronics / rf-microwave

author: Qmavam
author_rank: Regular Contributor
timestamp: September 10, 2019, 03:51:26 pm
content: I have a E core with a large 0.225" gap.I put 337 turns on it and measure the inductance at 401mH.From that I calculate AsubL at 3530.But that seems way to high, with that gap.What have I got wrong?Mikek

author: Qmavam
author_rank: Regular Contributor
timestamp: September 10, 2019, 04:35:08 pm
content: I think I might have figured this out, but I need some confirmation.I put a winding on the outer legs of the E coreTesting one coil 337 turns I get 401mHTesting the other387 turns I get 528mH.In series aiding, I get 1819mH.But what is the flux doing?I think it is ignoring the center leg and almost all of the flux flows in the outer legs.I should have connected the coils series opposing and then the flux would be forced to flow in the gap.Mikek

author: duak
author_rank: Super Contributor
timestamp: September 10, 2019, 06:05:04 pm
content: You've got it - the reluctance of the air gap is higher so it has much less flux than the outer legs.For the most part, If you connect the coils in opposition, the MMF (Magneto Motive Force - Amp-turns) just cancels. However, the flux in the gap may increase. If you do this with DC you should see if an iron object is attracted more or less to the gap. Let us know.

author: Qmavam
author_rank: Regular Contributor
timestamp: September 10, 2019, 07:50:26 pm
content: Finally, things are making sense.I put two coils on the core, one on each outside leg, around 100 turns each.One coil measures15.12 mH, the other 21.12 mH.Series aiding 74.23mH.Series opposing 2.97mHWhen I put a tight fitting toroid in the gap, the inductance changes.Series aiding 75.89mH with toroid in gap vs 74.23mh with open gapSeries opposing 13.95mH with toroid in gap vs 2.97mH with open gap.It made no sense before when I saw so little change of inductance when I filled the gap.Now with series opposing connection I see a large change.I only wound 200 turns, 100 on each coil, this is about 1/3 of the previous coils.I applied about an amp, yes there is a magnetic pull to each side of the gap.I put the toroid with turns making a 124uH coil into the gap and varied it down to 11uh.I ran a series and the current is about 3 times more than it was when I had the 724 turns.So now all is right with the world.Next problem, how do I find the permeability of the E core material.However I measure it the core AsubL is right at 3500.It seems to me, using the area, volume or maybe magnetic length,I should be able to back into Effective permeability and and then interpolate for Relative permeability.Any help there? The Ecore has these dimensions,
2 meter preamplifier for sale - Page 1
Forum section: electronics / rf-microwave

author: bob91343
author_rank: Super Contributor
timestamp: September 10, 2019, 11:01:14 pm
content: Maybe this isn't the place to post this; if so, I apologize. I searched for a swapmeet place to no avail.Anyway I have a tiny pramplifier I will never use. Here are a couple of pictures as well as a frequency plot.Open to price or swap.Bob K6DDX

author: bob91343
author_rank: Super Contributor
timestamp: September 10, 2019, 11:03:17 pm
content: Doesn't seem that the attachments got through.

author: tautech
author_rank: Super Contributor
timestamp: September 11, 2019, 04:17:52 am
content: Pop a duplicate posting here for better exposure:https://www.eevblog.com/forum/buysellwanted/