hybridfree/eevblog-posts huggingface dataset:
Zero ohm voltage source - Page 1
Forum section: electronics / rf-microwave

author: R_G_B_
author_rank: Frequent Contributor
timestamp: May 17, 2020, 11:31:01 am
content: Hi,I built a VCO circuit that would work using the analogue discovery wave gen as a voltage source to drive the VCO circuit. However when I decided to build my own voltage source using a op27 to drive the VCO it would not work I noticed the op27 output impedance must be too high. I read the reference manual for the analogue discovery wave gen and also the forums state it's wave gen has a zero ohms option.Indeed setting the output to 50 ohms on the bnc adapter board the VCO would not change frequency. Setting it back to zero the VCO functioned as expected. I now need to create a low impedance voltage source close to zero. Maybe aDifferent opamp such as a FET type? I did try over opamps such as those in the PSOC. Can anyone offer any suggestions. Help appreciated.R_G_B

author: Kleinstein
author_rank: Super Contributor
timestamp: May 17, 2020, 11:58:35 am
content: AN OP like the OP27 wired as a voltage follower is pretty close to zero ohms output impedance, at least for the lower frequencies. I is actually more like a few µH and thus can start oscillating or at least tend to ring if too much capacitance is added.The normal VCOs use a varactor diode or two at the input. This does not require a low impedance drive signal, so 50 Ohms would be perfectly OK.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: May 17, 2020, 12:17:04 pm
content: Thanks I can look and try to find a more suitable opamp that's able to drive the VCO.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 17, 2020, 04:57:56 pm
content: Using a PSOC suggest a relatively low voltage. The OP27 needs quite some supply voltage and has a limited common mode range. With a low voltage one may need a single supply or Rail to Rail OP (e.g. LM358, LT1013, MCP6001). Noise and drift may also be a factor that can be important.

author: tggzzz
author_rank: Super Contributor
timestamp: May 17, 2020, 05:12:46 pm
content: Quote from: R_G_B_ on May 17, 2020, 11:31:01 amShow the circuit schematic, the tests, and why you came to your conclusion (and therefore your remedy).Without that we are flying blind. Personally I doubt your conclusion is correct.
Video: 3rd order Intermodulation Distortion basics, and the effect in a receiver - Page 1
Forum section: electronics / rf-microwave

author: w2aew
author_rank: Super Contributor
timestamp: May 07, 2020, 02:35:08 am
content: I recently posted a video that covers the basics of 3rd order IMD (intermodulation distortion), including some of the basic effects inside a radio receiver and how simple front end attenuation can help to alleviate the problems caused by it.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 07, 2020, 09:26:56 am
content: Please go back to pencil and paper style, with live operated instruments on a workbench, with circuits and wires, pointing to the signals on the screens and so on, not computer graphics.Thanks for all the great videos!

author: w2aew
author_rank: Super Contributor
timestamp: May 08, 2020, 01:11:38 am
content: Quote from: RoGeorge on May 07, 2020, 09:26:56 amI certainly will. This video is an offshoot of something I did for work, so that's why it has a little more of a professional (less personal) feel to it.

author: paul002
author_rank: Regular Contributor
timestamp: May 27, 2020, 12:06:10 pm
content: I agree, the paper and pencil approach is what we really enjoy. Also as an amateur how can I measure this with limited equipment. I just got rid of all the spurs of my DDS VFOnow I am looking at my first mixer which is now a common 4 diode balanced mixer, maybe to replace it by a jfet mixer in common source or common gate. Interesting to see some of these in comparison. But I like the video's you make. Thanks
RF amp simulation with MicroCap - Page 1
Forum section: electronics / rf-microwave

author: Yrrah
author_rank: Contributor
timestamp: May 17, 2020, 12:01:13 pm
content: Hello,I am simulating a simple RF amplifier, as part of an oscillator I want to built. I use MicroCap 12, for free now. I am having trouble getting the results I expect, and measured at my VNA. I guess the transformer is incorrect. The idea is to simulate the complete oscillator. I already have the crystal where simulation and measurement matches fine. Please advise.Harke
MOVED: Picking RF ceramic capacitors and SMT inductors (experimenters sample kits?) - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: May 16, 2020, 03:55:08 pm
content: This topic has been moved toBeginnersbecause it's a very basic question.https://www.eevblog.com/forum/index.php?topic=242306.0
Feeding a high input amp, load xformer, don't load? - Page 1
Forum section: electronics / rf-microwave

author: Qmavam
author_rank: Regular Contributor
timestamp: May 20, 2020, 06:33:13 pm
content: I have a FET follower RF amp. It is a high input impedance ~330kΩ and a 100 Ω output impedance. I have it on an antenna that has a 330 Ω output impedance. The antenna works fine NOT being terminated with 330 ohm,i.e. it's fine seeing the 330kΩ load of the amp input.The amp does two things, it doesn't load the antenna so I get about 2 times the voltage output. Second, it does an impedance conversion, in this case a 1.8 voltage gain over the step down of a matching transformer. That all conspires to be ~ 9.8db of gain.My question with the caveat, that over driving the input of an amp willcause unwanted problems.(but how far can I push it)Now, say I put a step up transformer on the antenna to feed the amp input, say 1 to 3, i.e. 330 Ω to 2,970 Ω, a 3 X voltage step up.Now I have 3 times the voltage on the input of the amp. and another~10db of gain. That seems to come at no cost, unless I start to over drive the amp.My question: The antenna impedance is 330 ohms, I wind a transformer that is 330 Ω to 2,970, that would be driving a 330k Ω circuit.That's seems to be a problem, but maybe not, the antenna would just see the transformer as a much higher impedance, just as it originally saw the amp, when it was connected directly to the antenna.I would think the antenna sees a inductive reactance load instead of a resistive load. The obvious solution would be to put a 2,970 Ω resistoron the amp input.Do I calculate the inductance of the primary any different than usual since the secondary is unloaded? Should I just add the resistor.Here's a schematic of the amp.>https://www.dropbox.com/s/x6z2vpbseri7ysu/2%20FET%20Troubleshoot.jpg?dl=0Your suggestions please.Mikek
Yaesu SCU-17 show up as unknown device?! - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: April 23, 2020, 01:39:31 pm
content: I had that device before on my pc and the did work. Sadly my USB over Glasfiber didnt work so I had to install a fresh Win7. Everything else work beside of the Sound Modem Yaesu SCU-17.When i connected it to a USB 3.0 Card the show up as unknown device on my USB 2.0 the worked.So what could be? On the old Win 7 installation the did work before.When I try to manually install the driver the show "unknown device" is the current driver?!Any idea?Thanks

author: arno
author_rank: Contributor
timestamp: April 28, 2020, 04:21:33 pm
content: Hi,I have had issues with my Yaesu FT991A on USB 3.0 ports as well, USB 2.0 works (Thinkpad with Arch Linux).73 de DL2SSB

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 11, 2020, 11:34:58 am
content: I connect it with my Thinkpad (W7) via Glasfiber - USB and it works there.
Questions about microstrip array antenna - Page 1
Forum section: electronics / rf-microwave

author: promach
author_rank: Frequent Contributor
timestamp: May 10, 2020, 08:11:14 am
content: 1. Why is 100 ohm transmission line used inthis microstrip array antenna?2. WhyA quarter-wavelength transformer of 70 ohm is used to match the impedance line of 100 ohm to the impedance line of 50 ohm.?3. Would abutler matrixbe better than these simple impedance transformers in terms of reducing MIMO diversity issue ?4. Is thisstacked array antennadifficult to realize ?

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: May 10, 2020, 12:51:34 pm
content: You should really avoid asking the question here, and on the /r/rfelectronics and on stackexchange, or at least tell people. It is somewhat frustrating to find out that after spending half an hour answering your questions, it's all already been solved by the guys at /r/rfelectronics and you probably won't listen/need any more help.

author: radiolistener
author_rank: Super Contributor
timestamp: May 10, 2020, 09:55:48 pm
content: may be for impedance matching and phase shifting between elements for directivity adjustment.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: May 11, 2020, 08:32:38 am
content: Quote from: radiolistener on May 10, 2020, 09:55:48 pmIndeed. The specific question was answered on Reddit as well.If you do the math, you will find that to match 100 ohm to 50 ohm with a quarter-wave transformer, an impedance of 70 ohm is about ideal.Most of the line impedances in the paper can be found with simple first-year EM course matching networks.
PCBs for a RF active probe and a noise generator - Page 1
Forum section: electronics / rf-microwave

author: profdc9
author_rank: Frequent Contributor
timestamp: May 07, 2020, 01:39:06 am
content: So I got the RF active probehttps://github.com/profdc9/ActiveRFProbeand the Noise Sourcehttps://github.com/profdc9/RFNoiseSourcebuilt up. I am waiting for some equipment so I can test these better. There are a few bodged 220 ohm resistors in there and I had to swap out the regulator. But I will see if they actually meet specifications.

author: awallin
author_rank: Frequent Contributor
timestamp: May 07, 2020, 05:31:57 am
content: would the probe run on +5VDC from USB? Most new scopes have USB at the front panel so this would be convenient instead of finding a +9VDC source (or is the idea to cable-tie a 9VDC battery to the PCB?)what is the lower right output (2 terminals) in the schematic?looks interesting, please post measurement results - especially if you do get towards 1 GHz BW

author: profdc9
author_rank: Frequent Contributor
timestamp: May 07, 2020, 01:04:30 pm
content: The probe would work fine from 5 VDC. You might have to some extra filtering on the supply. I intended it to work from a 9 volt battery to minimize noise as it seems to be very sensitive.The RF probe also has a peak detector on it (a 1N5711-type low capacitance Schottky diode) for slow scopes or just measuring power.
Do I need that additional RF amplifier? - Page 1
Forum section: electronics / rf-microwave

author: technix
author_rank: Super Contributor
timestamp: May 06, 2020, 06:40:17 pm
content: Since I got that IKEA Zigbee Light Link bulb, I need a Zigbee dongle to talk with it, and I plan to build it myself. The core of the design I have in mind is AT86RF231. I do have a chip balun for AT86RF231, and I plan to use a ceramic chip antenna for it. Now I am wondering if I should insert an RF switch/PA/LNA combo chip, AP1286S, between the balun and the ceramic chip antenna? (AT86RF231 have two digital IO pins, DIG3 and DIG4, when configured to reflect internal RF switch status, can control AP1286S correctly, including RX, TX and sleep modes.)
Damage and/or degradation of magnetic circulators - Page 1
Forum section: electronics / rf-microwave

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: May 15, 2020, 01:45:08 am
content: Can anyone shed some light on the effects of external magnetic fields on those components?When I took that question to our supplier, I got some harrumphing and was reminded that any metallic object (correct would have been any object with a permeability significantly different from air) does influence the behaviour of the circulator, i.e. will detune it.But that was not what I was after, as I have looked for permanent effects. My current understanding is that this would depend mainly on the coercitive field strength of the permanent magnet in use.Or is there any effect on the ferritic material too?To put it on a wider base, any information on the failure modes, effects, and underlying causes that affect those components is welcome!

author: Wolfgang
author_rank: Super Contributor
timestamp: May 15, 2020, 02:08:03 am
content: ... just from personal experience:- Have not experienced any significant effect when mounted on (nonmagnetic) metal.- tried to keep line transformers, ... away. Might have been overcautious.- Had some old ones with bad VSWR and shifted center freq. Suspected fading permanent magnet, but didnot crack them up.- If you kill them, its normally by too much power and/or missing terminations- generally fairly robust and long-lasting parts, IMHO- dont drop them, however. The magnets are normally brittle and can crack.

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2020, 03:21:38 am
content: look into inductor stability to get an idea of what mechanisms can effect ferrites. I would imagine any effect that causes a measurable electrical change in the ferrite material used in the circulator (imagine it was taken out and used to make an inductor and measured before and after the 'damage'), would effect the waveguide in some way.Some inductors drift quite nastily, unfortunately for the junk box power electronics salvage guys. As far as the specific material used in circulators, I don't know.Possibly a relevant start on research:https://www.mouser.com/pdfdocs/Doc1192_Notes_on_thermal_aging-2.pdfhoweverDetails of the exact materials used by Coilcraft and other inductor manufacturers are undisclosed, being proprietary information, so it is not feasible to make exact predictions on the lifetime effects of thermal aging. Nor is it feasible to make definitive statements of suitability for use in any particular application. The information provided here is based on the test results described with the single intent of informing about the thermal aging phenomenon in iron powder cores.And, MWave is probably even worse in terms of secrecy.
Looking for service manual with schematics; HP8505A VNA - Page 1
Forum section: electronics / rf-microwave

author: nnills
author_rank: Contributor
timestamp: May 02, 2020, 09:21:16 pm
content: I recently bought a "working" HP 8505A VNA. But after only the most rudimentary of tests I found that it only worked between 640MHz and 660MHz(middle of the max 1300MHz frequency). The LO warning light is on while the sweep is outside of that range. When out of that range it also has a noisy signal and the amplitude is way off. Also the frequency counter only works in that range.The service manual that I found only shows way's of measuring the performance and making adjustments(manual on xdevs.com). I found a seller on ebay who claims to sell a service manual with schematics and theory of operations but i think it can't hurt to ask here(mainly for the manual. But if you have an idea why this problem happens feel free to tell me!)Thank you in advance

author: Tony_G
author_rank: Super Contributor
timestamp: May 03, 2020, 03:21:31 pm
content: Artek manuals have some with Schematics in them -http://artekmanuals.com/manuals/hp-manuals/TonyG
Q Factor & DC Current of Inductor - Page 1
Forum section: electronics / rf-microwave

author: thelearner
author_rank: Contributor
timestamp: May 02, 2020, 05:48:20 am
content: Hello,I am using Skyworks 66420 for my design. In the reference design, they used inductors with the following specifications1. Package = 0402(1005 metric)2. Maximum DC current = >500mA3. Q minimum = 8 to 20To reduce the size I want to use 0201(0603 metric) packages for my design. I couldn't find inductors with the same Max. DC Current specification. The total current consumption of the SKY66420 is around 350mA.So can I select the inductors with Max. DC Current of 350mA?In SE2435L reference design, they used inductors with Max. DC Current of 300mA, whereas the total current consumption of SE2435L is 450mA.What is the effect of Max. DC Current on filter circuit?What are the parameters to be considered while selecting an inductor for a filter circuit?What is the optimum value of Q to be considered while selecting the component?TIASKY66420 Reference Design:https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/2801-2900/SKY66420_11_204006G.pdfSE2435L Reference Design:https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/601-700/SE2435L_202412K.pdfRegards,thelearner

author: radiolistener
author_rank: Super Contributor
timestamp: May 02, 2020, 10:45:40 pm
content: Quote from: thelearner on May 02, 2020, 05:48:20 amUsually smaller inductor size means worse Q factor (smaller Q), because smaller inductor uses more thin wire, so it has higher resistance, higher loss and low power.Quote from: thelearner on May 02, 2020, 05:48:20 amDC current doesn't matter for filter, but it can be used as indirect indicator for inductor max power limit on high frequency. More thick wire will have higher DC current specification, so inductor with higher DC current most likely supports higher power.if you use low power signal, it doesn't matter for filter. For high power signal (such as transmitter output) you will need more thick wire for inductor for low loss, because even a small loss for high power can damage inductor with heating. If inductor uses core (metal powder or ferrite) it is even more critical, because high power may damage inductor core, so you're needs to make sure that inductor core supports expected power level.Inductor core material also affects working frequency range.Quote from: thelearner on May 02, 2020, 05:48:20 amThe main inductor parameter for filter circuit is Q factor.Higher Q factor means lower loss and more sharp filter slope.Also make sure that inductor has proper working frequency range.Quote from: thelearner on May 02, 2020, 05:48:20 amHigher Q means better filter performance, so it depends on filter performance which you want to achieve.In short:
[Solved] Any QS1R owners on the forum ? Looking for Revision D schematic - Page 1
Forum section: electronics / rf-microwave

author: chris_leyson
author_rank: Super Contributor
timestamp: March 12, 2020, 09:02:49 am
content: Just wondering if there are any QS1R owners on the forum, I've lost my copy of the Rev D schematic and I haven't heard back from Phil N8VB, not surprised to be honest. Would be nice to add a few features maybe.Been using my QS1R as an EMC test receiver recently and using the wideband FFT feature really speeds up.RegardsChrisThanks OH2LIY

author: charliedelta
author_rank: Regular Contributor
timestamp: May 02, 2020, 04:56:58 am
content: Does the QST have a Quasi peak detector and EMC bandwidths like CISPR 9khz?I really dont know why there is not a single SDR receiver with a Quasi peak detector and CISPR bandwidths? Its just a simple programming job not a hardware mod.
Odd mini whip problem - Page 1
Forum section: electronics / rf-microwave

author: veedub565
author_rank: Frequent Contributor
timestamp: April 12, 2020, 09:38:19 pm
content: Hi, I'm currently using a mini whip on HF. I've noticed that when listening in on a good signal, switching the power on or off to the mini whip makes little if any difference to the signal.The box of tricks for the mini whip is grounded to an earth rod. The rig is grounded to an earth rod.It's weird that with no power to the mini whip, and the shield (presumably) grounded, it still pulls in a signal.Any ideas ?

author: charliedelta
author_rank: Regular Contributor
timestamp: May 02, 2020, 04:44:41 am
content: That should not happen, unless its not working at all and the feedline is working as the antenna since the signal is strong?Another possibility is that the power supply capacitors are fully charged and is still powering the antenna.I have about 10 different active whips and when i shut the power off all signals disapear. Maybe as a temporay measure power it from a battery and then disconnect and see what happens.
Harmonics of RF Front End Modules - Page 1
Forum section: electronics / rf-microwave

author: thelearner
author_rank: Contributor
timestamp: April 21, 2020, 06:27:11 am
content: Hello,I am using Skyworks Front End Module SKY66420-11. In the datasheet, it is specified that maximum power at 2nd harmonic measured with continuous-wave is +7dBm(Max) at +27dBm output power(Table 5). But in the performance characteristics graphs(Figure 9), the maximum power at 2nd harmonic is approximately -15dBm at +27dBm output power.So what value is to be considered?TIALink to datasheet -https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/2801-2900/SKY66420_11_204006G.pdf

author: OwO
author_rank: Super Contributor
timestamp: April 21, 2020, 07:13:22 am
content: Bet you they confused dBm with dBc. 27dBm - 15dBc = 2dBm, add some margin and you get the 7dBm maximum 2nd harmonic spec.

author: thelearner
author_rank: Contributor
timestamp: April 21, 2020, 09:35:41 am
content: No in the data-sheet is specified in dBm only.

author: OwO
author_rank: Super Contributor
timestamp: April 21, 2020, 09:56:19 am
content: That graph is wrong; the units are dBc and not dBm.

author: miken
author_rank: Regular Contributor
timestamp: April 29, 2020, 03:14:34 am
content: Figure 9 is Typical, not guaranteed. Table 5 is a Specification, stating the worst case. You would want to do your own qualification testing for the part to see how much you trust the "typical".
Wet coax cables and MHz transmission - Page 1
Forum section: electronics / rf-microwave

author: aussie_laser_dude
author_rank: Contributor
timestamp: April 26, 2020, 09:18:02 am
content: Hey guys,my understanding is that wet coaxial cables are bad because they could electrically short. Is there, for small amounts of moisture in a coax cable, an effect on bandwidth transmission due to maybe a change in dielectric properties?Another way of asking this is: would a 300 MHz signal be attenuated more/less than a 600 MHz signal when a coaxial cable (say 50 / 75 ohm impedance) is subjected to minor water damage?I'd love to try this out with a spectrum analyzer and a piece of coax but unfortunately I have no such equipmentThanks for any help

author: David Hess
author_rank: Super Contributor
timestamp: April 26, 2020, 02:55:08 pm
content: Wet coaxial cable has much greater loss which increases at higher frequencies; the loss at VHF and UHF can be considerable. This is a good reason to use cables which are resistant to damage from water in exposed locations.

author: richard.cs
author_rank: Super Contributor
timestamp: April 27, 2020, 12:52:18 pm
content: Air spaced coax can also have the disappointing feature of acting like a pipe and channelling water into your equipment. This used to be a common problem associated with TV antennas and the "low loss" coax with the hollow polythene spacer.

author: David Hess
author_rank: Super Contributor
timestamp: April 27, 2020, 09:11:30 pm
content: Quote from: richard.cs on April 27, 2020, 12:52:18 pmAir spaced coax can also "breath" causing condensation on the inside which then accumulates.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 27, 2020, 11:18:52 pm
content: Quote from: richard.cs on April 27, 2020, 12:52:18 pmIt was quite shoddy, but there was nothing fake about its low losses.I remember during a Telethon, we had to set up some domestic TVs to be fed from a UHF CCTV feed carrying programme material, where the sound could be turned off separately from the normal feed, for operational reasons.We ran out of the "crappy" coax, for a fairly long run, & tried to substitute RG59, but the signal was unuseable.We had to run around like "headless chooks" to get some of the air core stuff.Next Telethon, we organised a "workaround", & could use AV feeds instead, so the problem went away.RG6, which is widely used now, doesn't have spectacular loss figures, but is really durable.Proper air spaced coax, like that used to feed TV transmitting antennas, is pressurised, either with dry air from. a dehydrator, or nitrogen.
A Circular-Polarization Reconfigurable Meng-Shaped Patch Antenna - Page 1
Forum section: electronics / rf-microwave

author: promach
author_rank: Frequent Contributor
timestamp: April 27, 2020, 01:30:12 pm
content: Have anyone simulated thisantenna with chinese character?What is the purpose of the pin diode in this antenna ?

author: coppice
author_rank: Super Contributor
timestamp: April 27, 2020, 02:32:57 pm
content: Are these special anntenae for use on the walls of red houses?

author: promach
author_rank: Frequent Contributor
timestamp: April 27, 2020, 02:35:19 pm
content: I do not understand how the pin diode in the paper actually related to circular polarization
Yet another similar project, a noise source - Page 1
Forum section: electronics / rf-microwave

author: profdc9
author_rank: Frequent Contributor
timestamp: April 24, 2020, 12:24:57 am
content: So I was thinking of using the 2SC3356 reverse biased emitter-base junction as a noise source, being a wideband transistor with a low breakdown voltage. So I drew up an idea of my own.I use a 10k resistor on the base on the noise transistor, and a ferrite bead and a PCB inductor on the emitter to try to not ground either side of the noise source, as to direct the noise into the emitter follower (high impedance) stage. Think this is a viable solution? Here is the projecthttps://github.com/profdc9/RFNoiseSourceI include the PCB layout so you can see the inductor as well as the current schematic here.

author: David Hess
author_rank: Super Contributor
timestamp: April 24, 2020, 08:53:45 pm
content: I have thought about breakdown noise sources for a while and I think what I would do is use a pair of sources with a differential amplifier to reject any influence from the supply voltage. Then I might use three sources with three differential amplifiers so failure can be detected.

author: fourfathom
author_rank: Super Contributor
timestamp: April 24, 2020, 10:02:21 pm
content: I don't see how the ferrite bead or the PCB inductor help. The noise from your E-B breakdown source needs a current path to generate a voltage across the 10K resistor. The series inductance will attenuate the high-frequency noise. You should at least add a RF bypass capacitor from the emitter of the noise junction to ground. You also want a RF bypass at the regulator output, that 22uF does nothing at high frequencies.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 24, 2020, 10:25:17 pm
content: Not totally offtopic, but a sidestep request, please.Whatever schematic you'll choose in the end, please measure the noise amplitude and spectrum when brand new, vs. later in time, after many hours or weeks of continuous functioning, and publish the results here. I've read that reverse polarized BE junction tends to "wear out" with time, and the noise level become much lower.
Subtracting Noise from Measured Signal - Page 1
Forum section: electronics / rf-microwave

author: TeddyPython
author_rank: Contributor
timestamp: April 19, 2020, 03:33:58 pm
content: Hi, I'm currently reading through CISPR 11. Annex C describes a method for removing background radiation from a spectrum measurement (under certain conditions). It gives this as:Where Eg is em disturbance, Et is measured field strength, and Es is field strength of noise source you want to remove (all in uV/m). I presume the 1,1 is the European way of representing a decimal number (1.1), but I am unsure why these values are raised to power of 1.1. Where does this come from?

author: Kalvin
author_rank: Super Contributor
timestamp: April 20, 2020, 02:20:35 pm
content: As I understand it, the given formula is empirical approximation which gives sufficient accuracy for the practical purposes under the given conditions. (Yes, the exponent is 1.1).

author: TeddyPython
author_rank: Contributor
timestamp: April 20, 2020, 04:28:07 pm
content: Understood, thanks very much Kalvin.
Programmable bandpass filter for SDR - Page 1
Forum section: electronics / rf-microwave

author: srce
author_rank: Regular Contributor
timestamp: April 23, 2020, 08:32:49 am
content: Are there any ideas for an electronically programmable bandpass filter circuit, that can be tuned over a wide range (100MHz to 6GHz) that would be suitable for use before the input of an SDR? (Possibly after a wideband LNA). Bandwidth could probably be fixed, but if that were tuneable too, then even better.I'm guessing there probably isn't, at least not easily, as most SDRs I've don't seem to have them, and seem to have separate filters for different bands, but maybe there are some ideas out there?

author: David Hess
author_rank: Super Contributor
timestamp: April 23, 2020, 12:38:14 pm
content: Switched filters are the easiest way however it is common for higher performance receivers to use LC based tracking preselectors controlled by varactor diodes for each band; this greatly improves overload performance. Varactor diodes can also be used to tune helical resonators for even better performance however the tuning range is limited.A YIG based preselector could be used over a much wider frequency range and I suspect some military receivers intended to operating under hostile conditions include this.

author: MarkF
author_rank: Super Contributor
timestamp: April 23, 2020, 01:04:16 pm
content: I think you will find this video interesting:Agilent 8445B Auto Preselector

author: 9aplus
author_rank: Regular Contributor
timestamp: April 24, 2020, 08:03:40 am
content: Here using whole old ICOM PCR-1000 like preselector for LimeNET microTaking the signal out at 10,7 MHz IFThan go up - conversion to 74,3 MHz with moRFeus, because Lime RX input performs better on VHFAll that is now boxed in one pelican case like Wifi/Ethernet remote RX system useful from 150 kHz to 1,3 GHzFirst remote set PCR on the begining of band of interest, for example 50 MHz than can browse through500 (800 max) kHz up, which is seen like 74.3 to 74.8 MHz on Lime. Software is Soapy Remote plus CubicSDR.Preparing to extend up with one SHF 4 Ghz mixer from Anaren but still considering how to manageBPF for 1,3 GHz to 4 GHzSystem now running on AC 220 V but preparing to go on 24 V DC and generate all lower voltages on clean RF side19 V, 12 V, 5 V

author: M0HZH
author_rank: Regular Contributor
timestamp: April 24, 2020, 09:10:17 am
content: As David Hess said, there are two options: the simpler one is switched octave bandpass filters (good performance), the more complicated one is switched narrowband tracking bandpass filters (best performance). For the second one, varactor diodes, DACs and some software magic is necessary. For the first, good PCB design and a VNA are enough.A switchable narrow band-stop filter for the 2.4GHz WiFi band might be useful if you want to look at low signals in that segment and you find local WiFi is oveloading your receiver. The same with 88-108MHz broadcast.
Looking for a datasheet; Avantek UTC10-113M LNA - Page 1
Forum section: electronics / rf-microwave

author: 0culus
author_rank: Super Contributor
timestamp: May 01, 2020, 05:40:19 am
content: At the title says. I got this LNA (pictured) in a grab bag of RF parts, and I've struck out trying to find a datasheet for it. It's a 5-1000MHz LNA that runs on +15 Vdc. I confirmed via tracking generator testing that it indeed shows a bandpass that meets label specs, and has a nearly flat gain between 14.6-15.2 dB across the rated bandpass, after which performance degrades rapidly. However, I'd like to compare my findings to a datasheet if possible.Thanks!

author: rfeecs
author_rank: Frequent Contributor
timestamp: May 01, 2020, 05:52:50 pm
content: You may might find something similar here, but not the exact part number:https://archive.org/details/avantek_Avantek_Modular_and_Oscillator_Components_2nd_ed/page/n13/mode/2upOften these were semi-custom made, tweaked to the customer's requirement. The catalog parts just served as a starting point.

author: 0culus
author_rank: Super Contributor
timestamp: May 01, 2020, 07:21:06 pm
content: Thanks! I'll look through it. If anything, the key for decoding what the model numbers mean provides some insight.
High-frequency trading and directional Radio Communication - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: April 24, 2020, 04:22:57 pm
content: HiRecently on ARTE (a French - German TV Station) have a report about High-frequency trading and Microwave directional Link.The bought an old Antenna Station and build there own Radio Network. When I heard about how much the payed it sound insane.Does anyone here come in touch with such?(For everyone who speak Austrian: Die Geldroboter)

author: 0culus
author_rank: Super Contributor
timestamp: April 24, 2020, 04:39:34 pm
content: Also, these companies pay huge premiums to have datacenter space as physically close to them as possible. Possibly tens of millions of dollars to have their rackspace on a certain side of the datacenter.

author: ogden
author_rank: Super Contributor
timestamp: April 24, 2020, 04:44:42 pm
content: It's physics. Signal in the optical fiber travel slower than EM waves in the air.

author: Lord of nothing
author_rank: Super Contributor
timestamp: April 24, 2020, 04:53:10 pm
content: QuoteHow is a Stock Exchange connected to the rest of the Internet?What I know ISP use a Peering point to connect with each other in Vienna its the VIX.Does a Stock Exchange peer on such Peering Point to?

author: ogden
author_rank: Super Contributor
timestamp: April 24, 2020, 04:56:42 pm
content: Quote from: 0culus on April 24, 2020, 04:39:34 pmThere are more than single type of HFT. Those who are trading in the single stock exchange, usually uses co-location services offered by exchange itself. Those who build radio networks usually are connected to at least two stock exchanges, they are Hi-Freq "flash traders" - they obtain information in one exchange to trade in another.

author: ogden
author_rank: Super Contributor
timestamp: April 24, 2020, 05:12:12 pm
content: Quote from: Lord of nothing on April 24, 2020, 04:53:10 pmVia firewallHi-freq traders do not use "common internet" for connection but direct link to datacenter of exchange instead. Internet is full of info about this stuff. Just one resource to mention:https://www.investopedia.com/
Dipole Ends - Page 1
Forum section: electronics / rf-microwave

author: veedub565
author_rank: Frequent Contributor
timestamp: April 10, 2020, 07:13:49 pm
content: Hi, bit a of a newbie question. If I loop the ends of my dipole back on itself and fix with a cable tie, will this affect the tuning ? i.e. will folding the ends over tune it the same as trimming it ?I'm not planning on soldering the looped over end back onto itself, I'm just looping it over and through a dogbone insulator so I can keep some tension on the wire.

author: Ian.M
author_rank: Super Contributor
timestamp: April 10, 2020, 07:30:42 pm
content: How long is the dipole (measured to the tip of the loop) and how long is the looped end? Unless you are working at (or above) VHF frequencies, the loop is almost certainly entirely negligible. However I wouldn't trust plastic cable ties to hold a wire under tension outdoors, as they will loose strength due to UV exposure. A Talurit crimp splice, at least TWO cable clamps or a tight racking seizing done with wire and well tarred to reduce corrosion would be vastly preferable. Insulated wire is a different problem - the core will slip within the insulation under tension if its only held by the insulation, therefore you need to use a knot that does not kink (and thus weaken) the standing part of the wire. I suggest a buntline hitch.

author: bd139
author_rank: Super Contributor
timestamp: April 10, 2020, 07:32:59 pm
content: It'll be fine on HF and yes it has the same effect as trimming. My dipole was folded to about 8 inches over itself round a dog bone insulator. Just make sure you tie the conductors close together rather than dangling and it'll be fine. I got 1.2:1 easily with that and didn't need a tuner.

author: veedub565
author_rank: Frequent Contributor
timestamp: April 10, 2020, 07:56:47 pm
content: Sorry I should have said it's a fan dipole for HF with various elements. It's loft mounted so not outdoors and the wire is PVC insulated. I never thought of the core slipping within the insulation. It doesn't need a lot of tension in it, just tieing up the ends to stop them drooping down. The elements are supported along their length (it's running through electric fence insulators fixed to the rafters)

author: Ian.M
author_rank: Super Contributor
timestamp: April 10, 2020, 08:13:36 pm
content: No worries then. As its supported at points throughout its length and there's no wind swaying it I doubt there's enough stress to cause the wire to slip and as there's no UV, black nylon cable ties should be fine.

author: tkamiya
author_rank: Super Contributor
timestamp: April 19, 2020, 03:48:25 am
content: If your wire is insulated, you loop around and twist, its electrical length will be somewhere between the total wire length and folded length. On HF, it really doesn't matter. I used to do this all the time. It works just the same.
Trio TS-120 help needed please - Page 1
Forum section: electronics / rf-microwave

author: christopher iles
author_rank: Regular Contributor
timestamp: April 12, 2020, 06:38:52 am
content: Hello,I have a TS-120s with no receive, just a faint hiss from the speaker.Checks so far:VFO is good, digital readout on all bands is fine.I have checked the voltages on every pcb and they are all correct.I have scoped the oscillators and they all are present.When I connect a signal generator to the antenna socket, I see it on the input of the rf board but not on the rif out.So, I injected 8.83MHz on to the rif input on the IF board..still nothing.If I pull the 2 pin connector (+14v and RB) off the IF board I get white noise out of the speaker.Obviously, I have checked that the rf gain pot and all other controls are set as they should be so the radio SHOULD WORK!I've checked all the devices on the IF pcb and the board for dry joints, broken tracks etc and all appears ok.It's starting to baffle me now; any help would be GREATLY appreciated, thank you.73, Chris G0VOE, Somerset, Southwest England.

author: 9aplus
author_rank: Regular Contributor
timestamp: April 12, 2020, 08:11:20 am
content: You may check RED voltages on Q1 to Q4if ok, than follow the RF signal along the path...that band pass filter switch may be source of trouble.schematic sourced from:https://www.qsl.net/wb4kdi/Kenwood/#TS-120Scope may not be enough to follow the signal along the path,spectrum analyzer or wideband SDR with buffer preamp. canbe useful.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 12, 2020, 08:25:54 am
content: Try to bypass the band selector. This is a mechanical device and considering the age of your radio might be worne out. Do also check the diodes D2 to D5. If that don't help i would put a signal on the antenna socket and start to trace it along the signal path.LA9XNA

author: christopher iles
author_rank: Regular Contributor
timestamp: April 14, 2020, 06:20:19 am
content: Thank you for the reply.Am I correct in assuming the top voltages are rx and the lower voltages are tx?They are BOTH in red!!Kind regards,Chris.

author: 9aplus
author_rank: Regular Contributor
timestamp: April 14, 2020, 11:48:07 am
content: Quote from: christopher iles on April 14, 2020, 06:20:19 amYes, that may be.Put some dummy load on ANT and test.

author: tkamiya
author_rank: Super Contributor
timestamp: April 19, 2020, 03:42:57 am
content: You said VFO is good, but what and how exactly did you test? As I recall, TS120 has a provision for an external VFO. That means there are relays and rotary switches that hasn't been moved for 20 years maybe? I'd check that....Fixing HF gear from that era happens to be my favorite pass time. Almost every time, the issues are switches and relays. Attenuator switch (which TS120 does not have) are common issues. Band switches, ditto. VFO switches, too. Next up in antenna relay.I'd very much doubt mechanical issues. While you are in there, also be on a look out for potential modifications. It wasn't unusual to remove CW filter when selling a radio. If SSB filters were removed too, it will result in exactly the same scenario.Good luck.
Combining Matching Circuit Components in Series (2.4GHz Chip Antenna) - Page 1
Forum section: electronics / rf-microwave

author: NickAmes
author_rank: Contributor
timestamp: April 16, 2020, 03:58:40 am
content: Hello all,Being a newbie to RF design, I'd like to get your thoughts on if it's ok to combine two series inductors in a matching network. I'm trying to connect an nRF52811 Bluetooth IC and a Johanson 2450AT42E010BE chip antenna. The nRF52811 datasheet specifies a 3.9nH inductor between the antenna pin and the 50 ohm transmission line. Likewise, the antenna datasheet specifies a 1.5nH inductor from the transmission line to the antenna input pin.If my transmission line is short (less than 5mm, which is less than 1/20th of the wavelength), is it ok to combine the two components into one 5.6nH inductor? Logically it seems like that'd be fine: if there's no transmission line in between (since the distance is so short), then I just have two series inductors.Thanks!

author: ThomasDK
author_rank: Regular Contributor
timestamp: April 16, 2020, 09:41:27 pm
content: Quote from: NickAmes on April 16, 2020, 03:58:40 amYou will need to do your own matching network. The shown value is just what is needed on the evaluation board. Note that the antenna is pretty narrowband in the first tuning example - ideally you would want at least 6dB RL over the whole band of interest.From the datasheet:Quote
50 Ohm Impedance matching  - Page 1
Forum section: electronics / rf-microwave

author: thelearner
author_rank: Contributor
timestamp: April 13, 2020, 06:06:59 am
content: Hello,I am using a Skyworks Front End Module SKY66423-11. In the datasheet, they have specified to terminate the unused RF pins with 50 ohms. So how can I terminate the TX_ALT pin of SKY66423-11 with 50 ohms?TIALink to datasheet -https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/2801-2900/SKY66423_11_204566H.pdf

author: ogden
author_rank: Super Contributor
timestamp: April 13, 2020, 07:06:12 am
content: No. Most likely TX and TX_ALT pins are connected internally. It means that you have to leave TX_ALT pin floating. It is done so in the evaluation board as well.

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: April 13, 2020, 07:07:07 am
content: As I read it, if you're not using TX_ALT, you should leave it unconnected. I base that on these 3 observations:The photo of the evaluation board (Figure 3) shows that path entirely unpopulated.Both of the schematics, Figure 4 and Figure 5 show the series resistor unpopulated.Tables 5 and 6 specify their test conditions as "all unused ports terminated at 50Ω, unless otherwise noted". I think this is a lazy description of their test conditions and not instructions that you must terminate every single unused pin. I kind of doubt they actually put a 50Ω resistor on TX_ALT. In any case, I think my first 2 observations above are enough.

author: thelearner
author_rank: Contributor
timestamp: April 13, 2020, 10:25:23 am
content: Hello,I am not able to get +27dBm output from that front end module. I have used the same schematics with minor changes. I am using it for 868MHz design.The changes areRemoved a 0.6nH inductor which is is series with VCC1 pinRemoved ferrite bead at VCC0 pinRemoved 4.7uF capacitorLink to datasheet -https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/2801-2900/SKY66423_11_204566H.pdfHow can I get +27dBm with +8dBm input power?TIARegardsLearner

author: ogden
author_rank: Super Contributor
timestamp: April 13, 2020, 12:53:12 pm
content: Quote from: thelearner on April 13, 2020, 10:25:23 amHow much do you get? 26.9dBm?Apart from stating actual figure, it is worth to tell *how* you measure - whole setup. Describe not only what you use but tell all variables necessary to replicate your measurement.QuoteDid you design matching network accordingly- for 868MHz? Please tell more about layout - it is copy of evaluation board? If differs then how? Could you share pic of layout itself and populated board as well? What kind of inductors you use - mfg and partno?
Odd Comparison - Page 1
Forum section: electronics / rf-microwave

author: 4asifm
author_rank: Newbie
timestamp: April 14, 2020, 12:04:25 pm
content: Hi All,I am looking for an oscilloscope - I am mostly interested in homebrew, ham and such.I have an offer of a Agilent 54616B 500MHZ 2GSa/s (OLD) and Siglent 1202X-E (NEW) for about the same price. Once is a digitizing scope another a digital scope. I also understand that Agilent doesn't have the fancy FFT transforms and advanced math functions of the Siglent. But then higher sampling, single-shot bandwidth etc makes it very attractive. But the Agilent is old, discontinued and probably if it goes bust on me, I wouldn't be able to repair it or get it repaired.I am mostly interested in HF (below 100 Mhz) work in homebrew. For homebrew and HAM work is higher frequency bandwidth a better option over advanced math functions like FFTThoughts?This is my first post - please ignore any mistakes I made

author: OwO
author_rank: Super Contributor
timestamp: April 14, 2020, 02:43:11 pm
content: For RF work you want the maximum possible bandwidth. If you want to accurately see the waveform on a power amplifier you need to be able to see at least up to the 5th harmonic, preferably more. I would personally ignore any scope without a 50ohm input. You won't be using the math functions, because anything calculated will be horse shit since there is no such thing as measuring voltages and currents at RF; the voltages you see will bear little relation to reality and the only thing you should expect to see is the waveform shape (not even that if you don't get your probing technique right).

author: TheMG
author_rank: Frequent Contributor
timestamp: April 14, 2020, 07:32:05 pm
content: I find FFT on scopes not to be all that useful for this type of work, especially when you want to look at things like harmonics and IMD. You really want a spectrum analyzer for that type of stuff. Even a 40 year old analog spectrum analyzer will blow away any affordable oscilloscope's FFT function when it comes to looking at harmonics and distortion products that are many tens of dB lower than the fundamental. The FFT function just doesn't have the dynamic range required, and has other limitations compared to a spectrum analyzer.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: April 15, 2020, 12:58:47 pm
content: Quote from: OwO on April 14, 2020, 02:43:11 pmIf you are probing a system with 50 ohm impedance, the voltage very much will be sensible. The statement that there is no such thing as measuring voltages and currents at RF is simply not true. Sure, it requires a bit more finesse and you can't just stick a probe somewhere, but you really can still talk about voltage and currents.