hybridfree/eevblog-posts huggingface dataset:
NFC Antenna design - Page 1
Forum section: electronics / rf-microwave

author: iak
author_rank: Newbie
timestamp: July 06, 2018, 10:08:43 pm
content: Hello people,Just a general question. I was looking at some PCB NFC antenna design from NXP and I have noticed that they go in an interesting fashion.Lets say I have a 3 loop NFC PCB antenna. It looks like NXP route half of the first loop before jumping into the second with a via and half of the second before jumping to the third by via, the third loop is finished before returning to the second half of the second loop and then it return to the second half of the first loop [Something like this photohttp://www.entras.cz/images/foto/microcontroller/IMG_1440_up.jpg]. Why is it routed like this, I was expecting something like it finish the first loop and jump to the second without any via and then finish the second loop and jump to the third without any via and then finish the third and return to the beginning with two vias something like thishttps://b2bsol.panasonic.biz/semi-spt/apl/en/tool/nfcdesignnavigator/image/Caution_Gerber.JPGApparently both approaches are widely used but I see the former more, what is the reason of doing that. What advantages does it have, any reference when designing the shape of an NFC antenna.Also I have seen some commercial NFC antenna where the middle of the tracks is connected to GND, why is that so like when it goes through half of the antenna, the track is connected to GND using a VIA before returning to the start, why is that.I would really appreciate if anybody helped with these two question. A referenced answer where I can read more from the sources would be great, as I am having trouble finding a good source for general practises used when designing NFC antenna.Thanks !.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 07, 2018, 06:16:23 am
content: Just how the PCB designer decided to do it.The interleaved turns will have more self capacitance, which is generally undesirable for an inductor, actually. But this is well below the self resonant frequency, regardless, so it makes little difference.Tim

author: iak
author_rank: Newbie
timestamp: July 07, 2018, 10:02:49 am
content: Yeah, I guess. But there should be a reason why somebody would make it more complicated by going half of each turn, while he can simply do it the other way.Most NXP antenna with devkits are designed this way, yet I cannot seem to find any document that explains why.Any comment about connecting the the middle of the antenna to GND. Why from my point of view you would be expecting the voltage level halfway through the antenna to be 0 ?.Thank you for your comment.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 07, 2018, 06:22:24 pm
content: Centertapped is better: the voltage is balanced around zero, so the net electric field at a distance is zero. This gives lower RFI and better selectivity to near field objects. This may be a reason behind the interleaving.Tim

author: iak
author_rank: Newbie
timestamp: July 08, 2018, 11:24:19 am
content: Thanks Tim. That kinda make sense now
ultra narrow band antennas? - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: July 10, 2018, 01:23:28 am
content: What is the most narrow band antenna that can be made? Is it a thin dipole? Are there any tricks?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 10, 2018, 02:50:55 am
content: Superconducting resonators have Q up in the 10^7 range, open a pinhole on that and you'll have an antenna with mediocre efficiency and a more than uselessly narrow bandwidth.Presumably such a structure could be miniaturized, as a small helical resonator open to space (a Tesla coil as it were), rather than a nearly-closed Helmholtz resonator; at significant cooling cost, of course, given present technology.Tim

author: hagster
author_rank: Frequent Contributor
timestamp: July 10, 2018, 07:46:18 am
content: The trouble with very narrow band antennas is that they are very easily detuned. This could be because of nearby materials(or people) or even temperature/humidity changes.Typically electrically small antennas are narrow band. Much of this is due to the matching network needed to maximise efficiency.An easy to envisage example is the small tuned loop. You can add more turns to the loop to increase the radiation resistance, but also increases the inductance and the required shunt capacitor size needed to match. The LC circuit becomes more and more narrow band and susceptible to slight changes in L or C.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 12, 2018, 11:25:31 am
content: For the practical, everydays use us radioamateurs normally use short loop-antennas with a variable capacitor as tuning element. In case of an environment with a lot of QRM, such a loop can give a better S/N-ratio than a dipole
LMS7002M sourcing - Page 1
Forum section: electronics / rf-microwave

author: mrf184
author_rank: Contributor
timestamp: July 01, 2018, 11:13:29 am
content: There are many projects where I need many cheap I/Q transceivers with high bandwidth (10MHz or more); using a discrete solution (synthesizer chip + quadrature demodulator + baseband filter + amplifiers + adc) uses a lot of pcb area and isn't cheap, so LMS7002M seems a better idea. However it is difficult to source, with most distributors pricing it at $110 which is way too expensive (it probably has 2x margin from the distributor) and more expensive than the discrete solution. I'm trying to find a better source for it, and it seems no one is selling it on taobao/aliexpress yet. Does anyone know of a better way to get this chip or any alternatives?
testing shielding on my acoustic probe? - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: July 01, 2018, 12:05:01 am
content: So I put a tiny buffered smd microphone on a stick (shiskabob skewer) along with some ferrite and decoupling capacitors, shielded cable, twisted pair. It was kind of tricky to build but I basically used copper tape and some silver epoxy to make a seal going down to the braid/foil on the cable. The body of the microphone is metal and I connected it to the shield with the silver epoxy. It uses very thin wire (like 32 AWG for about 2 inches, the ceramic SMD cap and ferrite are basically super glued to the microphone, and dead bug solder bridged, then this is glued to a stick, 2 inches away the wires go to a larger tantalum cap/ceramic cap, then a large gauge 4 conductor double shielded cable is used, with 2 of the wires being used for power and 2 for signal (the power will be provided by a battery), the signal will go into a commercial filter box. The whole thing is coated with nonconductive epoxy up to the microphone body, then copper tape/silver epoxy is used to basically extend the shield over everything.. the only opening being the tiny slit for the microphone. The microphone is about the size of a 1210 package. I zip tied the 4 conductor cable to the stick, covered it well with epoxy and put heat shrink on top of it to make a half decent handle.What's a good way to test immunity on it.. if I use an inductor I expect it to make some acoustic noise in addition to the fields it produces.Since the microphone tops out at like 100KHz (really like 50KHz), I can't really use a proper antenna to make a field, because it would be gigantic..Actually I don't even know if a low frequency antenna vibrates mechanically.The only idea I had is to make some kind of foam block to stick the probe in that would hopefully dampen any mechanical vibrations, and maybe keep it in the same place to see if adding the foam reduces any of the signal levels. Something like a couch cushion came to mind, but I wanted to test it on fairly strong fields, meaning placing it right against the inductor face so its being exposed as much as possible, or making some kind of like air-gapped coil or helmholtz coil to make a field.Would winding field-generating inductors on a piece of foam help, so there is foam between the wires and the core? Cotton sleeves on the magnet wire?I was gonna use a nicely shielded directional industrial pickup coil good to around 70KHz to act as my indicator or field strength
primary inductance of mini-circuits transformers - Page 1
Forum section: electronics / rf-microwave

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: June 30, 2018, 02:25:25 am
content: Hi,I'm trying to find a 1:1 mini circuits TX that has around a 5uh primary inductance to use in a tuned circuit.Can't find any data on the mini-circuits site. Has anyone compiled any data on this?Cheers,Corby

author: ejeffrey
author_rank: Super Contributor
timestamp: June 30, 2018, 04:20:32 am
content: You can download S parameters for most minicircuits parts. You can figure out what you need from that.
Sirio CXL-4 70 MHz antenna, teardown and repair - Page 1
Forum section: electronics / rf-microwave

author: FransW
author_rank: Frequent Contributor
timestamp: June 19, 2018, 01:35:13 pm
content: The attached article describes the adventures with a Sirio CXL-4 70 MHz antenna.A few days after installation the newly bought antenna appeared to automatically reduce the output power of my transciever.The swr of this antenna had changed from 1: 1.1 to infinite.Construction information was hard or not to find.So, we (a friend of mine and myself) investigated the problem and subsequently solved it.Regards, Frans

author: videobruce
author_rank: Frequent Contributor
timestamp: June 25, 2018, 01:05:24 pm
content: Excellent 'fix' .pdf. Far better than another u-boob video.What service uses 70MHz in your country?

author: FransW
author_rank: Frequent Contributor
timestamp: June 25, 2018, 05:01:01 pm
content: Hi videobruce,The 70.000 to 70.500 MHz segment is primarily used by radio amateurs.For use of the 70 - 80 MHz band in the Netherlands see attached pdf.Regards,Frans
Anyone familar using a RLB with feed lines & wide band antennas? - Page 1
Forum section: electronics / rf-microwave

author: videobruce
author_rank: Frequent Contributor
timestamp: June 24, 2018, 10:20:34 pm
content: I have two runs a cable running to two discone antennas. Attached are screen saves of the scans of each with and w/o a 50 ohm load attached. The pics are labeled "up" & "low" representing the location on the mast of each antenna. All fittings are 'N'. The RLB is a Eagle RLB150N5A.The cables are;Unknown (unlabeled) RG8/U: 50' (labeled "upper")Shireen RFC400: 60' (labeled "lower")There is also a 5' jumper w/ a lightning arrested (which I forgot they were there or I wouldn't of included that in the test).My question is do these scans look 'normal' (acceptable) or does anyone see issues here? I was troubleshooting possible reception issues, the reason for the thread.

author: videobruce
author_rank: Frequent Contributor
timestamp: June 25, 2018, 12:41:22 am
content: Just to be clear, no antennas were attached. The sweeps labeled 'load' were the reference dummy load only.I'm just interested in the feed lines themselves.
GHz PLL/VCO LMX2594/5 Any Hands-on Experience? - Page 1
Forum section: electronics / rf-microwave

author: Mr Simpleton
author_rank: Unknown
timestamp: July 03, 2018, 09:44:11 pm
content: The TI LMX2594 or 2595 looks very very sweet... Having a single IC capable of generating signals from 10 MHz to 15 or 19 GHz is pretty mind boggling! Curious if anyone here have had a chance to play with this and how hard it is to get all 100+ registers properly set. Know there is software to help, but there are so many holes to trip into. Thinking of getting the EVM, priced at ~$400 it looks like a great deal as a low noise reference is included.Information in the data sheet is very limited vs. what you see in similar products from Analog. No typical spur plots, nor switch time graphs, makes me a bit worried.... Analog is still showing its 15 GHz PLL/VCO as advanced info, and not currently available.

author: hendorog
author_rank: Super Contributor
timestamp: July 03, 2018, 09:53:11 pm
content: No experience yet, but I'm just starting on a board. I'm going to use the LMX2572 as a cheaper option for the first one - pretty sure it is pin compatible with the LMX2594/95.

author: Mr Simpleton
author_rank: Unknown
timestamp: July 03, 2018, 10:24:06 pm
content: Cool! Looking forward to read about your findings....

author: Lukas
author_rank: Frequent Contributor
timestamp: July 03, 2018, 11:20:44 pm
content: I'm just in the process of getting a board that uses the LMX2595 (originally LMX2594, but that one happened to be out of stock) for LO generation. Like a miracle, it locked pretty much on first try using the default configuration that came with the TI software. In the next few weeks, I should get around to measure some more specific performance figures.

author: Mr Simpleton
author_rank: Unknown
timestamp: July 04, 2018, 07:05:42 am
content: Oh the 2595... 19 GHz, that is spectacular.If you can make some spectral plots showing spurs and such, would be greatly appreciated!
Video: Basics of Bias Tees - including applications and demonstration examples - Page 1
Forum section: electronics / rf-microwave

author: w2aew
author_rank: Super Contributor
timestamp: June 20, 2018, 08:09:24 pm
content: Bias Tees are RF components that are used whenever you need to couple a DC, power or low-speed control signal onto an RF signal path. This video discusses the basics of Bias Tees, how they work, examples of practical construction and a few lab application examples showing them "in action". Links for the Bias Tees used in this video, as well as a copy of the video notes are here:https://www.minicircuits.com/pdfs/ZFBT-4R2GW+.pdfhttps://www.minicircuits.com/pdfs/ZX85-12G+.pdfhttp://www.dorkage.com/youtube/Basics_of_Bias_Tees.pdf

author: w2aew
author_rank: Super Contributor
timestamp: June 21, 2018, 03:30:33 pm
content: Quote from: Mechatrommer on June 21, 2018, 12:51:10 pmI hope you enjoy it when you get home!

author: LapTop006
author_rank: Unknown
timestamp: June 21, 2018, 07:00:26 pm
content: Great video as usual.Happens that I need to build a custom DC blocking terminator for a project, your explanation was better than those I've seen so far, but I still need to find a deeper background to really understand value selection for DC blocks.

author: w2aew
author_rank: Super Contributor
timestamp: June 21, 2018, 07:16:33 pm
content: It all depends on what frequency range you need. The high-pass corner on the low frequency end is easy F=1/(2*pi*C*R) where R is sum of the source and load impedance. The upper frequency will depend on capacitor selection (dielectric, physical configuration, etc.) which will determine the cap's self-resonant frequency. For really broadband high-performance DC blocking, you might want to look at the parts from Presidio - see page 10 in this catalog:http://www.presidiocomponents.com/catalog/RF-MW-FOBrochure6100RevI-May2018.pdf

author: LapTop006
author_rank: Unknown
timestamp: June 22, 2018, 04:15:51 am
content: Quote from: w2aew on June 21, 2018, 07:16:33 pmI'm rather more down to the DC end of things, some neat reading though, the SONET references do date the text rather amusingly.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 22, 2018, 05:16:33 am
content: An interesting thing is how as our target band goes up and up in frequency, the inductor becomes the easy part and the capacitor becomes an issue. The LC network can also serve as a lumped-element narrow-band matching network, and we use it on integrated circuits to tune out the gate capacitance of a MOSFET. And at some point we just give up on bias-Ts and switch to center-tapped transformers, where we use the center tap on both coils to bias the in/outputs of the system, and provide impedance matching.Excellent video.Seeing all those different cables - w2aew, do you make all your cables yourself?

author: w2aew
author_rank: Super Contributor
timestamp: June 22, 2018, 02:19:15 pm
content: Quote from: TheUnnamedNewbie on June 22, 2018, 05:16:33 amI only make a few - most of them are cables I've picked up over the years from a variety of places - ranging from online purchases to hamfest or flea-market finds.
RL of a port of a filter, need a 50ohm load on the other port ? - Page 1
Forum section: electronics / rf-microwave

author: jujun
author_rank: Regular Contributor
timestamp: June 20, 2018, 11:01:52 pm
content: Hello,I wonder if when metering the matching with a VNA of a port of a filter, is it best to add a 50 ohm load on the other port of the filter?I find that would be logical to do so, because I will use a near 50 ohm thing on this port.Sorry for the stupid question.ThanksJulien

author: jujun
author_rank: Regular Contributor
timestamp: June 21, 2018, 02:41:28 pm
content: So, I quickly tried by myself, and if I put a 50 ohm load, or without a 50 ohm load it's near the same.And if a put a short on the other input of the filter I have a very different RL curve.But when I plug nothing it's like I have an open, so why it doesn't change a lot?

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 22, 2018, 05:23:59 am
content: You always have to measure a filter with all ports terminated in their characteristic impedance. In fact, this is in the definition of s-parameters: \$S_{xy}\$ is the voltage wave out of port x, relative to the voltage wave into port y, with all other ports terminated in their characteristic impedance (note that this does not have to be 50 ohm, but whatever the impedance of the port is).Try adding a quarter wavelength of coax to the output, and then add a short and a load. If everything is working, you should see that the short suddenly behaves like an open, and the open suddenly behaves like a short. If the length of your output just happens to line up with a stub that matches to your characteristic impedance at your target frequency, it is in essence matched, just not with a 50 ohm resistor.
TNC Adapter (for CB Radio) - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: June 15, 2018, 11:15:59 am
content: HiMy Handheld CB Radio have an TNC Adapter and I will connect some Antenna.I found on Ebay some Seller who sell some TNC Adapter for ~5€.Are there any other idea for cheaper one?Thanks
How would you make this data transmitter wireless? - Page 1
Forum section: electronics / rf-microwave

author: Beamin
author_rank: Super Contributor
timestamp: June 11, 2018, 12:21:07 pm
content: I don't know where to start but I think I have the parts. I have those 433 MHz transceiver boards from ebay with the 3" stubby antennashttps://www.ebay.com/itm/CC1101-Wireless-RF-Transceiver-315-433-868-915MHZ-SMA-Antenna-Wireless-Module-/201473086248?_trksid=p2385738.m2548.l4275I have the two Arduino nanos and the screens from the video.Can you feed that yellow wire into the data lines on the transceiver?Or do you have to further modulate the signal to make it ready for RF or is that handled on the RF modual?This will be a challenging project for me as I want to make something that I created rather just following instructions. Remember I'm still new to this so don't say: "Just take an FPGA and convert to Manchester encoding using check sums for error correction." I need a simpler explanation.

author: Beamin
author_rank: Super Contributor
timestamp: June 11, 2018, 01:51:22 pm
content: So I found a flaw you have to send the clock signal over. Besides using a separate transmitter channel for the clock how do you mix the two together or is there a way to send where the clock doesn't matter?

author: IconicPCB
author_rank: Super Contributor
timestamp: June 12, 2018, 02:32:16 am
content: Have a look at Xbee modules.The can operate peer to peer or in a meshed cituation.Peer to peer mode is akin to a pair of wires data into transmitter data ut of the receiver.Thats data stream not data plus timing.

author: Lord of nothing
author_rank: Super Contributor
timestamp: June 13, 2018, 02:32:01 pm
content: I still want transmit Data who get Captures by an Phone to the others.Maybe there is still something on the Marked who works "offline".

author: Beamin
author_rank: Super Contributor
timestamp: June 14, 2018, 07:05:05 pm
content: Quote from: Lord of nothing on June 13, 2018, 02:32:01 pmChinese Data sheets are easier to understand then your post. What?Or is this google translates work?
Simple 2.4 GHz bandpass design - Page 1
Forum section: electronics / rf-microwave

author: rfspezi
author_rank: Regular Contributor
timestamp: June 14, 2018, 07:04:35 am
content: I am planing to build an 2.4 to 2.5 GHz bandpass filter (around 4th order) to improve out of band signal rejection for my WIFI RX preamp.Using Rogers PCB material is no option.FR4 is a no-go either.So i wonder what would be the easiest implementation in your experience?EDIT:It should be able to handle up to 36 dBm as the TX power also goes through.

author: yl3akb
author_rank: Regular Contributor
timestamp: June 14, 2018, 12:04:34 pm
content: Long time ago I verified that this interdigital BPF calculator works quite well:https://www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.phpI would not recommend too narrow relative bandwidths (<<10..20%) though. Here picture of my quick and dirty implementation:

author: rfspezi
author_rank: Regular Contributor
timestamp: June 14, 2018, 12:43:53 pm
content: Quote from: yl3akb on June 14, 2018, 12:04:34 pmThanks!This comb-line filter indeed looks fairly easy to build.Is there a reason why you did alternate the rod-grounding instead of having all rods grounded on the same side?Do you think threaded rods may also be used?

author: yl3akb
author_rank: Regular Contributor
timestamp: June 14, 2018, 01:17:04 pm
content: Actually this is interdigital filter which allows for less spacing between resonators for same relative (fractional) bandwidth in comparison to combline, in other words it is more compact.I guess threaded rods should work okay. Low surface loss of material is very important, if low insertion loss and/or narrow BW is required. I used tinned copper pipes, which could also be easily soldered to box walls.

author: yl3akb
author_rank: Regular Contributor
timestamp: June 14, 2018, 01:18:16 pm
content: Here is calculator for comb-line as well:https://www.changpuak.ch/electronics/combline_bandpass_filter_designer.php

author: CopperCone
author_rank: Super Contributor
timestamp: June 14, 2018, 01:54:17 pm
content: You can find a ton of wifi ones that work at that frq on ebay pretty cheap now with 5ghz fyi
lowest frequency waveguide ever made? - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: June 03, 2018, 02:12:47 am
content: Not counting horn antennas, what is the lowest frequency wave-guide made?The lowest commercial I found is WR-2300, which is good for 300MHzWhat are these used for? Are lower frequency wave guides used for anything? Usually I see high power coaxial line used instead of waveguides, but I figure there might be some interesting applications.Application of WR-2300http://slideplayer.com/slide/12972804/Synchrotron

author: Yansi
author_rank: Super Contributor
timestamp: June 03, 2018, 02:48:04 pm
content: Interesting stuff they have there

author: Richard Head
author_rank: Frequent Contributor
timestamp: June 04, 2018, 02:13:34 pm
content: I can't answer your question unfortunately but I watched a YT video the other day about the Arecibo radio telescope. They use waveguide for their 450Mhz transmitter and it looks like HVAC ducting!

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: June 04, 2018, 11:50:10 pm
content: I suppose it's all relative. Some folks who regularly work on W-band stuff visited my work, where the largest guide we use is WR-284; they looked like they'd seen a ghost.

author: dkozel
author_rank: Regular Contributor
timestamp: June 08, 2018, 01:36:27 pm
content: Waveguide I don't know, but I've seen coax that I could almost crawl through. This system runs at 233 MHz.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 08, 2018, 06:23:19 pm
content: I think I have seen some waveguides at FM frequencies. I think the main reason they are used is maximum power, which is limited in coaxial by dielectric breakdown. Losses could also be less of an issue but I don' t know how significant the losses are at these (relative to what I'm used to) low frequencies.

author: AF6LJ
author_rank: Unknown
timestamp: June 11, 2018, 12:01:33 pm
content: I remember seeing specs for waveguide that was made for 225MHZ, big stuff.

author: Wolfram
author_rank: Frequent Contributor
timestamp: June 12, 2018, 11:13:20 am
content: Quote from: CopperCone on June 03, 2018, 02:12:47 amWR-2300 waveguides were used between the klystrons and the accelerating cavities of the LHC at CERN when I was involved with that system, and as far as I know they are still using the same systems. Here is a document with more in-depth infohttps://cds.cern.ch/record/1287871/files/CERN-ATS-2010-192.pdf.

author: AF6LJ
author_rank: Unknown
timestamp: June 12, 2018, 12:57:03 pm
content: Thanks that will make for good reading.

author: jmelson
author_rank: Super Contributor
timestamp: June 12, 2018, 10:16:15 pm
content: When I worked at NASA Wallops Station, MIT had a big radar they used for space object tracking.It ran at either 450 or 900 MHz (conflicting online info), and the waveguide looked like industrial-scale air conditioning ducts.Jon
What is this RF item?? (SOLVED, RF power sensor bulkhead) - Page 1
Forum section: electronics / rf-microwave

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 12, 2018, 03:03:44 pm
content: Found this thing laying around, what is it??, It has a N Plug-Male on one side

author: Tony_G
author_rank: Super Contributor
timestamp: June 12, 2018, 04:27:57 pm
content: Looks like the bulkhead assembly from a HPAK 8400 series H-variant sensor. If you download the manual for the 8481H there is a procedure to test that assembly.Actually looking closer at the 2nd image, there should be 2 very fine gold wires coming from those little bumps on the ceramic insert (which will be the matched thermocouples (or diode detector if this is an earlier model). Anyway those wires feed into the input amplifier and are critical to the correct working on the unit - So if they're missing then it might already be dead or unusable.TonyG

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 12, 2018, 04:53:37 pm
content: Yes, spot on. Those two wires are broken. I managed to turn those 4 small allen screws and take out the ceramic insert.Should take the microscope out but I feel too lazy right now.

author: Tony_G
author_rank: Super Contributor
timestamp: June 12, 2018, 07:44:32 pm
content: Good write up of the thermocouple here -http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1974-09.pdfTonyG
this amp hour podcast may be of interest - Page 1
Forum section: electronics / rf-microwave

author: jonovid
author_rank: Super Contributor
timestamp: June 07, 2018, 05:20:56 pm
content: https://www.eevblog.com/forum/amphour/the-amp-hour-394-jeri-ellsworth-and-the-demise-of-castar/orhttps://theamphour.com/394-jeri-ellsworth-and-the-demise-of-castar/the amp hour - this two hour podcast may be of interest to radio amateurs.#394 – Jeri Ellsworth and the demise of CastARwoman did all the 3 amateur radio license tests..... on the same dayJeri Ellsworth talks about ham radio at the end of the 2 hr podcastJeri has been building a huge loop antenna 80m & 160m6000-10000V antennasstealth transceiver& more!more
MESFET vs diode mixers - Page 1
Forum section: electronics / rf-microwave

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: June 04, 2018, 11:44:57 pm
content: I've been staring at the data sheets for MESFET mixers (example: Mini circuitsHJK-372H+) for a while. They have excellent compression characteristics (+14 dBm P1dB), decent LO to RF isolation (> 45 dB at my frequency of interest) and the noise figure should equal the conversion loss (7.7 dB) since it's a passive device. All of these, particularly compression, look better than pretty much all of MCL's range of diode mixers, so there must be some reason diode mixers are still being sold. In other words, where's the catch? It can't be the high LO drive, a representative Level 17 diode mixer (SYM-30DHW+) is worse than the MESFET device in every metric, with the exception of LO port VSWR. What am I missing?

author: CJay
author_rank: Super Contributor
timestamp: June 05, 2018, 06:47:44 am
content: HJK-372 is almost twice the price of the SYM-30, the application might not need the extra performance thus wouldn't justify the extra cost.Given that they are using MESFETs I also wonder if perhaps they're more static sensitive than a diode mixer and prone to damage?
TEM mode coaxial ceramic resonators, how to use them ? - Page 1
Forum section: electronics / rf-microwave

author: jujun
author_rank: Regular Contributor
timestamp: May 30, 2018, 12:37:24 pm
content: Hello,I juste discovered that TEM mode coaxial ceramic resonators exists, and I didnt find a lot of information on them.Where can I find information on them ?Did you already used them in a design ?Thank your for your helpJ

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: May 31, 2018, 07:06:15 am
content: Arent these just bits of coax cut to size (to be crude, ofcourse they will be optimized to give reliable frequency behavior etc), which you can then use as a classic transmission-line stub/short/etc?Pretty much the same as your classic "Voodoo RF black magic" microstrip filters, just with better shielding.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 31, 2018, 09:02:30 am
content: I think I've seen these in (older?) mobile phones as duplex filters. Here's a bit information:http://www.exxelia.com/uploads/PDF/epsilon-90-1-4-v1.pdf

author: jujun
author_rank: Regular Contributor
timestamp: May 31, 2018, 01:44:51 pm
content: Thank youSo I can see it like an industrial version of a coax stub.A kind of SMD coax stub

author: JohnG
author_rank: Frequent Contributor
timestamp: May 31, 2018, 01:48:47 pm
content: The advantage over a typical microstrip or coax cable stub is that the ceramic has a much higher dielectric constant for the insulation between conductors. This lets one make it much physically smaller for a given resonant frequency.John

author: phenol
author_rank: Regular Contributor
timestamp: May 31, 2018, 02:32:08 pm
content: https://www.minicircuits.com/WebStore/dashboard.html?model=CBP-1034C%2Bi used that one in the past. Really low insertion loss in the pass band, but what the datasheet doesn't show are the higher harmonic modes that start to appear above 2 or so GHz.I've seen such resonators with loosely coupled varactors in VCOs of old Nokia mobile phones in the 70cm band. I guess they were trying to achieve superb phase noise far out from the carrier.
#167 Drake L4B Quick Fix - Page 1
Forum section: electronics / rf-microwave

author: Radio Tech
author_rank: Frequent Contributor
timestamp: May 29, 2018, 12:47:49 am
content: Someone dropped off a Drake Amplifier that had the smoke let out.Lets take a quick look and see if we can repair it.

author: AF6LJ
author_rank: Unknown
timestamp: May 29, 2018, 02:15:00 pm
content: Nicely done....

author: Radio Tech
author_rank: Frequent Contributor
timestamp: May 29, 2018, 03:30:38 pm
content: Thanks Sue. Was a easy fix on this one. Almost had decided it was not worthy of a video. But this is the third one I have seen blow that circuit out.
Pearce Simpson AM810 CB Radio - Page 1
Forum section: electronics / rf-microwave

author: Shock
author_rank: Super Contributor
timestamp: May 28, 2018, 05:28:29 am
content: Picked up one of these, so now I'm officially a HAM right? Just kidding.Kinda cute actually, anyone have the schematics, manual or service manual etc?What would be the best way to test the output without a proper antenna, swr or commercially made load? Hesitant to fire it up without a load on the output. Have an oscilloscope but just want a rough idea. As far as I'm aware it's been working anyway.Looks really simple and easily maintained inside, the outside is actually ultra clean and just a bit dusty. Even came with the bracket and a whip base but no antenna.

author: tautech
author_rank: Super Contributor
timestamp: May 28, 2018, 05:39:58 am
content: Looks pretty tidy apart from the dust.Member defpom has had a lot to do with CB rigs, check out his YT channel on the repairs he does on them.Fairly sure he doesn't connect an antenna until he needs to check receive/transmit.BTW if you can grab his attention he'll probably recognize the layout and point you to manuals.

author: Shock
author_rank: Super Contributor
timestamp: May 28, 2018, 06:16:03 am
content: Thanks I dropped him a message.It's probably only a cheap $199 job. Looks like I'm the first person inside, not really vintage material but could well be apocalypse proof.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: May 28, 2018, 06:18:33 am
content: The radio doesn’t ring a bell, that is a pretty old unit, I will have to check my files to see if I have anything on it.You could poke around my website RadioMods.co.nz to see if you find anything, I collected information for many years!

author: Shock
author_rank: Super Contributor
timestamp: May 28, 2018, 06:42:32 am
content: Quote from: TheDefpom on May 28, 2018, 06:18:33 amI'm thinking 1988 from the test sticker at the back (I put the cover back on). Says Hatadi Electronics Sydney Australia.Obviously not "vintage vintage" if you know what I mean, no bank of crystals means it's PLL right? I think they were more on 20 Channel units anyway.What can you recommend when firing it up and testing? I don't have much in the way of RF, or a radio test set or anything like that. Can I rig up a temporary antenna and approximate the tuned length?I was probably about 1988 the last time I actually saw a CB heheh.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: May 28, 2018, 06:57:07 am
content: As long as you don’t transmit you can use anything as a test antenna, it just won’t be optimal and won’t work well, but if you are going to tx then you need a proper tuned antenna or dummy load to avoid blowing the rf final transistor.
Hp 8555a / 8552a / 141t - Page 1
Forum section: electronics / rf-microwave

author: Gimba
author_rank: Newbie
timestamp: May 15, 2018, 05:24:22 pm
content: Hello everyone.First of all, I want to apologize for my poor English.I long time i want to buy spectrum analyzer, but since I'm a beginner, I do not want to extract some huge money for it. First of all, I need to learn so that older analyzers, which from time to time can and will be repaired, are most suitable for me.I found on ebay the old Hp 141t with 8555a and 8552a for very small money and I am thinking of buying it. The thing is not checked and the seller does not guarantee for him, that suits me because he leaves me with the ability to fix it (and learn). The screen works, which is very important. I'm interested in what kind of analyzer it is, whether it's good for a beginner and for learning, and what its performance is. Is it good for EMI tests? There are very few things on the forum about this unit, so i could not get information.I've never worked with the RF, I've never had contact with the spectrum analyzer, and I do not know how to make a comparison. So I have to ask.Thanks

author: mrfblf
author_rank: Newbie
timestamp: May 26, 2018, 06:51:47 am
content: Hello,the 141T / 8555A / 8552A analyzer is a remarkable piece of vintage equipment. It was even more so when it came out around 1970, setting a quality / useability / flexibility standard for decades. I think it is fair to say that this system was a historic milestone in RF measurement technology.However, at 40 to 50 years of age, any electronic equipment starts to develop problems. This spectrum analyzer is no exception, and repairing the machine is very difficult, often impossible without special test cables. Any repair requires a lot of other test equipment, not to mention a very deep understanding of RF electronics.Also, keep in mind that the equipment on the market today has often seen a lot of abuse. It is close to impossible to repair, for example, a burnt out front end in the 8555A.Regards,Martin
DIY antenna - element thickness? - Page 1
Forum section: electronics / rf-microwave

author: DTJ
author_rank: Super Contributor
timestamp: May 20, 2018, 06:17:54 am
content: I'm looking at building a simple omnidirectional digital TV antenna for RV use.I've found a design which uses a 26" diameter dipole (?) arrangement as per the attached pictures.Is the conductor diameter important?The designs seem to mostly use 1/2 copper tubing. For practicality I'd like to use something like 3mm galvanised (solid) wire rod to create the elements?Will this create a problem? Is the element diameter an issue?My intuition says element diameter wont matter but my brain says I should ask those that know....

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 20, 2018, 07:06:00 am
content: Larger diameter gives stronger coupling to space (lower Q, wider bandwidth), up to the point where the conductor fills half the space of the antenna itself (give or take), at which point, the negative space being cut off by the conductor reduces bandwidth again.The widest bandwidth designs are self-similar, where the positive and negative space are equal, under the symmetry of the antenna. The type of symmetry defines the directivity and polarization: translational symmetry (similar along an axis) gives unidirectional response, rotational symmetry gives circular polarization, etc.So, if you want a modest bandwidth, like, uh, probably 30 to 50%, for something about that size and dipole-like (I guess it's not a dipole, but perhaps a folded dipole, loop, rhombic or such; anything electrically resonant-sized), you're probably about there. But if you're going for wideband, like octaves or more, you'll want something bigger like a log periodic.Tim

author: DTJ
author_rank: Super Contributor
timestamp: May 20, 2018, 12:25:37 pm
content: Thanks Tim.I read your reply and went ahead and built it. I ended up using some 1/4" solid aluminium round bar/rod.It seems to work quite well. Cheers.

author: CopperCone
author_rank: Super Contributor
timestamp: May 23, 2018, 01:55:08 pm
content: There are tables online that can show you bandwidth vs frequency for different rod thicknesses on dipoles.Iirc a like 800MHz dipole at 1/4 inch has bandwidth of like 70MHz

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 25, 2018, 02:19:01 pm
content: Quote from: DTJ on May 20, 2018, 06:17:54 am26 what? m, cm, mm?an Half Tubing? Why do you cut the Tube?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 25, 2018, 07:13:25 pm
content: Quote from: Lord of nothing on May 25, 2018, 02:19:01 pm" is short for "inch", defined to be 2.54cm.He probably meant 1/2" tube size as well, which by the way is different from pipe size ("1/2 inch" copper pipe is actually 5/8" o.d.), but flexible tubing is nominal (12.7mm o.d.).Tim
What is the current "Digital" Sound Mode on CB? - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 07, 2018, 10:48:53 am
content: HiI plugged my Sound modem to my legal CB Radio and run the ROS Software. Now the run for 24h and nada no response or Package received.So I know here are many People from around the World and which mode is use in your Country?ROS, VARA, PSK31?THX!!

author: Ghislain
author_rank: Regular Contributor
timestamp: May 10, 2018, 11:24:37 am
content: The short (legal) answer is none, I am afraid. IMHO except for Germany, data modes are strictly prohibited for CB operators.Of course, some people will always abuse the rules and regulations and therefore you are most likely to hear digital modes being used which are no different to what licensed amateur radio operators use.The most popular ones being PSK, RTTY, SSTV, WSPR, JT65, OLIVIA....FLDIGI is a popular software that allows working with many of the digital modes listed.

author: borjam
author_rank: Unknown
timestamp: May 10, 2018, 11:30:17 am
content: Quote from: Ghislain on May 10, 2018, 11:24:37 amDigital modes are authorized in Spain as well, on a strictly experimental basis and subject to the transmission power restrictions for AM (4 W), FM (4 W) and SSB (12 W PEP) transmissions.http://www.minetad.gob.es/telecomunicaciones/espectro/CNAF/notas-UN-2017.pdfI guess the rules are the same in all the EU. Or should be!In my opinion it's a good thing, CB is a very cheap way for people interested on amateur to test the waters, so to speak.And if you are interested on ROS activity on 27 MHz, you can use PSKreporter to check it.There is some activity on 27 MHz. Although these frequencies are not part of CB, so this is actually illegal activity. Butyou can use digital modes *legally* on CB frecuencies. Check Austrian regulations first, though.https://pskreporter.info/pskmap.html?preset&callsign=ZZZZZ&mode=ROS&band=26000000-27999999&timerange=86400&showsnr=1

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 10, 2018, 01:37:27 pm
content: My ROS Client is running currently on CB Channel 25 and I got some Replays today from France, Netherlands, Germany with the legal max 12W (do some people the Radio do just 10W on SSB).

author: borjam
author_rank: Unknown
timestamp: May 10, 2018, 01:56:00 pm
content: Quote from: Lord of nothing on May 10, 2018, 01:37:27 pmTry using pskreporter searching for your call. You might find out that you have been received far away.

author: CJay
author_rank: Super Contributor
timestamp: May 25, 2018, 03:41:40 pm
content: 35MVR001?Simple answer is there's absolutely nothing you can do because it's a made up CB callsign with no issuing authority to back it up so all you can do is ask them nicely to stop, then, when they refuse, you get to feel butthurt for a while before making up a new call sign

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 25, 2018, 03:47:58 pm
content: At the moment the System Automatic replay to his calls.I will try to get my new Handhelt CB Radio faster and will make some Bus rides to find the evil Person.
Did anyone hear anything strange on SW during the last eclipse? - Page 1
Forum section: electronics / rf-microwave

author: Beamin
author_rank: Super Contributor
timestamp: May 20, 2018, 08:23:53 pm
content: I just thought of this just now, but I will have to wait 6 more years to try it again. I noticed the best short wave is during sunset and maybe sunrise but haven't tried that. For about 20 minutes on some where below 12 MHz but that could be because of my antenna I seem to be able to receive all over asia from the US. In the US SW is plagued by recoding's of religious programing that's hateful and repetitive so it's not worth listening to other then checking to see what propagation is like since its the same voice from the same location. I was surprised to hear how factual the news was in places like india where they tell about crops and other survival things. Much different then hearing about celebrities personal lives.But the eclipse must have made all sorts of strange effects since that would be in between day and night and open close layers of the ionosphere not normally open unlike sunset. Much more exciting then looking at shadows or feeling the temperature change in the middle of the day which I wasn't expecting. In the mid Atlantic we had a partial eclipse where the normally bright day sun made everything look like it was a winter noon.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 21, 2018, 09:17:38 am
content: The various HF bands will come in & out of being "open".Hams have experienced & documented this over many years.

author: babysitter
author_rank: Frequent Contributor
timestamp: May 21, 2018, 09:18:53 am
content: Some hams compared stuff before the 2017 US eclipse to stuff during the eclipse. In 1999 during a european, I was listening on the 80m and heard what was similar to a day-night change.http://hamsci.org/basic-project/2017-total-solar-eclipse73,Hendrik
Putting DC voltages into a tapped transformer: how to do it - Page 1
Forum section: electronics / rf-microwave

author: ikrase
author_rank: Regular Contributor
timestamp: May 21, 2018, 06:27:54 am
content: I have a circuit that essentially is in the form of the attachment. A tapped-and-split transformer drives a resonant loop, and a DC voltage is applied to the split transformer (from moderate-output-current op amps)How do I connect this to op amps? Just straight connection? RF chokes?
What is meant by solid ground plane ? - Page 1
Forum section: electronics / rf-microwave

author: madhu.wesly01
author_rank: Regular Contributor
timestamp: May 04, 2018, 12:35:34 pm
content: Hi,I am unable to understand, what is meant by a solid ground plane?In the datasheets, some of the manufacturers mention 'Maintain a solid ground plane underneath the module'Does that mean'I shouldn't have any traces, vias underneath the module'or/and'I should have a continuous ground plane without any islands?'Please help me in understanding thisThanks in advance

author: Rerouter
author_rank: Super Contributor
timestamp: May 04, 2018, 12:59:51 pm
content: The overkill meaning is to have absolutely no breaks in the copper layer under the module what so everThe more realistic approach is to ensure any fast signals do not cross any breaks in a ground plane where possible, and to plan your return currents to make sure they can follow your signal.E.g. you have 2 signals that cross on the top and bottom layer, well the return current on a high speed signals wants to be as close to the signal trace as possible, generally following it on the ground plane underneath the signal, you have to allow a way for that return current to follow that signal past where it crosses the other to prevent it detouring around, which makes it both more likley to radiate noise, but also be suseptible to it.One approach would be to provide some via stitching around the crossing so each return current can jump to the other side, adjacent to the signal, continue past the break, then jump back down. its not perfect, but its far better than the alternatives.At higher speeds these breaks would also appear as impedance mis-matches, as the return current has to pass through a higher impedance per unit length of signal trace.And to set the concept straight in your head, generally when the voltage changes on a pin, there will be a current loop formed, from that pin it likely goes to the supply rail of that chip, through your voltage rail, to whatever other chips supply rail pin, then completing on its input pin.

author: German_EE
author_rank: Super Contributor
timestamp: May 07, 2018, 06:43:10 pm
content: In my experience a 'solid' ground plane is one that is unbroken by extra traces that couldn't fit on other layers. This is wht four-layer PCBs are so attractive, power and ground on the inside layers and signals on the top and bottom. Extra marks if you can keep the RF signals on the top and everything else on the bottom.

author: grifftech
author_rank: Frequent Contributor
timestamp: May 24, 2018, 05:41:58 pm
content: here is the opposite (Grid)