hybridfree/eevblog-posts huggingface dataset:
Coax length affecting reception - Page 1
Forum section: electronics / rf-microwave

author: veedub565
author_rank: Frequent Contributor
timestamp: December 03, 2016, 08:37:40 am
content: Hi,I built myself one of those chinese airband kits you see on ebay. It's all assembled into a metal project box and working well.The problem I have is that it works well with a 5m length of coax, but when using a 1m length then the reception is quite poor. Which seems a bit odd, I'm guessing maybe something to do with swr and matching?The antenna itself is a homebrew dipole at the appropriate length for civil airband.Really strange I seem to get more gain if you like with a longer feed coax

author: Paul Rose
author_rank: Regular Contributor
timestamp: December 03, 2016, 02:35:46 pm
content: I had a peek at e-bay. This look like a fun kit with a well designed circuit. I might have to get oneIncidentally, the circuit looks like it is from Tony van Roon's web site:http://www.sentex.ca/~mec1995/circ/aviarx/aviarx.htmlItcouldbe a impedance issue. A length of coax will transform the impedance of the load as seen by the source if the impedance of the source, load, and characteristic impedance of the coax don't all match.This can actually be put to use for matching:Zo = sqrt( Zs * Zl )Where Zo is the characteristic impedance of a 1/4 wave long piece of matching coax, and Zs and Zl are the source and load impedances. This is awkward to use, however, because usually Zs and Zl are set in stone, and you can't just order up an arbitrary impedance Zo coax to fit your need.Is your dipole acting like a dipole? Can you get a peak/null on a distant source by rotating the antenna? If not, then it may be that the whole feed line is acting as part of your antenna. Itcouldbe a balance issue. A balun at the feed point of the dipolemighthelp here. A receive only balun at this frequency should be easy to achieve, even an old VHF TV balun might be OK.

author: veedub565
author_rank: Frequent Contributor
timestamp: December 03, 2016, 08:28:22 pm
content: Thanks Paul,Been looking into it this morning and I think it may be a dodgy BNC connector on the kit. When I fitted the kit into a project box I used a bulkhead BNC salvaged from an old piece of equipment.I inserted the 1m length in between the receiver and the 5m length and the signal dropped right off. I tried 3 different 1m BNC leads and result was the same. I reattached the 5m length directly to receiver and jiggling the connector I was able to make the signal strength come and go. The connector on the 5m length must be making better contact than the others.So new BNC connector on order.I did try rotating the antenna but I was getting some strange effects due to the proximity of my hand, probably due to the dodgy BNC. I'll have to read up on Baluns.The kit has been fun to build, and a learning experience, which was partly the point. I could have bought a cheap readymade airband receiver for £50 or whatever, but this has been much more fun. I made some mods to improve it from standard too
HELP RFID NXP NTAG - Page 1
Forum section: electronics / rf-microwave

author: SwissEngineer
author_rank: Contributor
timestamp: November 29, 2016, 03:23:48 pm
content: Hello everyone,I'm not really good with RFID stuff so I am seeking some help!I'm trying to have a design using the NXP NTAG I2C plusNT3H2111_2211(http://www.nxp.com/documents/data_sheet/NT3H2111_2211.pdf)I have the demoboard and everything works fine, now I wanted to use another antenna to suit my needs:taoglas FXR.07.A.dg(http://www.taoglas.com/wp-content/uploads/2016/11/FXR.07.A.dg_.pdf)Because I need a round and with ferrite because I need to have it close to a steel product.But I can't get it to work!I am using the same design as the demoboard, with just a capacitor of 56pF between the leads of the antenna, and going directly to the chip.So what am I doing wrong?Thanks!
MOT Power Supply  - Page 1
Forum section: electronics / rf-microwave

author: dizz
author_rank: Newbie
timestamp: November 24, 2016, 07:33:45 pm
content: Hello EEVblogers. This is my first post here. I'm somewhat new to the electronics hobby if you call it that. I do work in a semi-related industry though as a cable splicer for ATT.I'm building a Power Supply [Microwave Oven Transformer....... rewound]. I have rewound the Xformer to 12.5v AC at the moment. Now it's time for me to build the rest.Sure, there are a ton of guides on Youtube etc but I have a few questions that I'd like to direct to the vast knowledge base that floats around here. The guide I plan to parallel is ...The video's author being Aussy (I assume) he's in 220v land. I'm US so I'm 120v.This really should have zero bearing on the inner circuitry though -correct? I mean once I've rewound my transformer to 120v : 30v, the rest of the video's circuits should work for me fine right?Happy Thanksgiving!!

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: November 24, 2016, 07:40:37 pm
content: Very neat construction. I have done this several times myself but not as neat. When you power it up what is the voltage? I assume you have a multimeter.

author: dizz
author_rank: Newbie
timestamp: November 24, 2016, 07:53:21 pm
content: Right now it's 12.5. Which is fine enough for a little power supply, but was considering making that a center tap and adding a few more windings for the main variable part of the supply.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: November 24, 2016, 09:23:58 pm
content: These make excellent power supplies. I found them cheap to get and am regulating them using a cheap thyristor to limit the current and adjust the voltage. I put this before the mains input. If you run these rewound MOT'S in staturation the can get quite hot so you can use a current sharing ballest resistor if you want more regulation. If you plan to make an arc welder then of course use the full power.

author: dizz
author_rank: Newbie
timestamp: November 24, 2016, 10:08:20 pm
content: I've seen those welders. Pretty cool stuff. It's not at all my intention to step up on this project. Might be fun (albeit dangerous) project in the future though. They kinda scare me a bit lol. I do respect those electronsMuch of what you describe are things I have not learned yet. I'm going to see what I can find online so it makes some more sense. Thanks for the reply and suggestions/advice

author: dizz
author_rank: Newbie
timestamp: November 24, 2016, 11:05:09 pm
content: Since this is going to be variable, I went ahead and soldered a tail at 15v and added another several windings. So now I have 3 terminal leads of which I can yield:6.27v15.08v21.38vfrom my 120v AC in.I could probably squeeze a couple more turns but there's not much more room for any more so that's probably gonna be it. Would have been nice to hit 25
APRS - any bit field expert? - Page 1
Forum section: electronics / rf-microwave

author: Dave_PT
author_rank: Frequent Contributor
timestamp: November 18, 2016, 07:19:04 pm
content: Hello.I want to make a little software to create the bit frames to send via AFSK, to the APRS network.Is there someone here who would like to help and / or collaborate with me?Thank you.

author: JimRemington
author_rank: Regular Contributor
timestamp: November 18, 2016, 09:57:25 pm
content: You can buy ready made modules or roll your own with Arduino (ATMega) or PIC processors. There are plenty of APRS tracker projects on line, too.Some leads at these sites:https://www.tracksoar.com/http://www.trackuino.org/http://unsigned.io/category/microaprs/(see also libAPRS for Arduino).https://www.byonics.com/

author: Dave_PT
author_rank: Frequent Contributor
timestamp: November 19, 2016, 06:10:25 pm
content: Thank you friend.Some I already knew, but some did not. I'll explore better.

author: dkozel
author_rank: Regular Contributor
timestamp: November 23, 2016, 05:57:25 am
content: Here's a report which talks in great detail about the APRS protocol.http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=2449&context=theses

author: Howardlong
author_rank: Super Contributor
timestamp: November 23, 2016, 06:46:10 am
content: Quote from: dkozel on November 23, 2016, 05:57:25 amThat looks like a really useful document, one that I could've done with fifteen years ago. Documentation around all amateur packet radio facets has traditionally been steeped in folklore and voodoo: only a very few ever really understood it to this level of detail.I'd also recommend that the OP look up FX.25, which is a backwards compatible FEC implementation of AX.25. Possibly the biggest drawback of AX.25 is the lack of FEC. Another is the modulation and coding scheme, but changing that would preclude backwards compatibility.I haven't read it all, but as an aside I did find it somewhat amusing that the author fights to map the stack to the ISO OSI straitjacket model: it looks like academia continues to peddle this massively over-egged and largely unnecessary abstract model made up of word soup that you learn by rote. I remember it being preached to me back in the early 80s at university, and when I asked for a practical example of it so I could better understand the abstraction, it was almost a tumbleweed moment. Since then ethernet and then TCP/IP have become unbiquitous and de facto, but both at the time and since then, there have been many other stacks that people feel the need to shoehorn into the OSI model, possibly the worst being the multiple protocols inside IBM's SNA architecture which were even more ill-fitting.
Converting Single ended to Differential Insertion Loss. Possible? - Page 1
Forum section: electronics / rf-microwave

author: hazuki
author_rank: Contributor
timestamp: December 09, 2016, 06:39:33 pm
content: Hi all,I have a project where I am trying to measure the differential insertion loss of a pair through a system with a VNA and then compare that to the basic model of the system where insertion losses for each component (connector, microstrip lines, cables, etc) are tabulated for each frequency and then simply added up. I am at a loss however to determine how single ended insertion loss compares to differential insertion loss when generating this table. For instance, I have single ended insertion loss per inch data for a particular dielectric that I am running differential microstrip over, but how do I translate this into a differential insertion loss per inch? I feel as though I would need some more information..Thanks

author: Earendil
author_rank: Regular Contributor
timestamp: December 11, 2016, 08:53:28 pm
content: According tohttp://www.magazines007.com/pdf/DC10_Loyer_Kunze.pdf:"Measuring differential insertion loss (SDD21) historically requires a 4 port VNA or TDT measurement, typically with 2 ports measured at one location, while the other 2 ports are measured at another location.""SDD21 is derived from four singleended measurements as SDD21=0.5*(S21-S23-S41+S43).""For ideal symmetric traces, S21 ~ S43 and S41 ~ S23. The equation then simplifies to SDD21 = S21 – S41."In actual manufacturing, the traces won’t be perfectly symmetrical."As for your last question inmy opinionthe answer depends on the differential pair's properties and cannot be answered generally.
Interesting Aerial Facilities PIN switch (?) - Page 1
Forum section: electronics / rf-microwave

author: wkb
author_rank: Super Contributor
timestamp: November 21, 2016, 07:52:11 pm
content: Found this cutie on a HAM fair here in PA country (the Netherlands).Manufacturer is Aerial Facilites Ltd, and it was hand marked as "70MHz" stuff. Does anyone on this forum have any info on this beast?I am curious about the 'coiled' interconnects between the chambers in the milled-aluminium box. It looks like very thin semi-rigid coax.Any clues?tnx Wilko

author: w2aew
author_rank: Super Contributor
timestamp: November 21, 2016, 09:38:54 pm
content: Those coiled sections could be 1/4 wave transmission lines, which could be used in switch applications for things like T/R switches. I did a video of one such PIN diode based T/R switch (using lumped elements instead of a 1/4 wavelength line). Here's the video on that, if you're interested:

author: raspberrypi
author_rank: Frequent Contributor
timestamp: November 22, 2016, 12:21:39 am
content: Great explanation answered all my questions too. Where do you buy the parts to make your inductors?

author: langwadt
author_rank: Super Contributor
timestamp: November 22, 2016, 12:46:37 am
content: Quote from: w2aew on November 21, 2016, 09:38:54 pmin NMR it is commonly done passively, basically the same circuit just skip the control and replace each diode with a set of antiparallel diodes

author: w2aew
author_rank: Super Contributor
timestamp: November 22, 2016, 03:21:33 am
content: Quote from: raspberrypi on November 22, 2016, 12:21:39 amI get a lot of my toroids from here:http://kitsandparts.com/or here:http://qrpme.com/?p=product&id=PT
Free Explore RF - Online training - Page 1
Forum section: electronics / rf-microwave

author: SKPang
author_rank: Unknown
timestamp: November 17, 2016, 02:27:47 pm
content: Free online training and ebook:http://erf-training.com/wolfspeed_signup.html

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: November 18, 2016, 03:52:15 pm
content: Anyone else take closer look ?I down loaded the ebook , and watched the 1st video .In the vain of trying to learn more about RF , I have my ham ticket and is the main reason for looking at , or my second - I seem to chase hobbies for a secondary reason - to learn & put in practice new skills .In this case electronics .Many others in the past , most recent benchrest shooting , I call it the most accurate type of shooting , example 5 shoots in 7 min. at 100 yrds , some of my better groups have been .032 of an inch , in practice and .082 in competition .I wanted to know how to do it , not just understand , but be able to do myself , did that for about 10 yrs. and partnered with a fellow shooter in his retied custom at home machining business , because that kind of accuracy can not be achieve with custom building with extreme tolerances .Well the same thing with ham radio , communicate around the world with very low power - how to do that , got my ham lic. and started playing with a new bunch of subjects electronics / RF .Do not have the time or money to go to school to become a electrical engineer , would like to .So back to the topic , this link .The 1st video was ok , would have liked to see examples during the overview of software , then I see that with most of the rest of the videos , there is a label saying no audio , that always puts me off , watching a video takes time and no audio leaves that time with less efficient / or lack of info ?Then not sure yet , but it may be a sales method , thats ok because of the effort put into the book & video .Looking for other views ?

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: November 21, 2016, 02:35:45 pm
content: Well , about 1/3rd of the way through it , and learning and reenforcing some of what I have learned - I need lots of repetition to pickup new thingsProblem is my math sucks .So this looks good ,
Best amp tube for low rf output  - Page 1
Forum section: electronics / rf-microwave

author: Jesset1996.5
author_rank: Regular Contributor
timestamp: November 17, 2016, 04:23:33 am
content: Hello, i am looking for suggestions for what tube i should use in my linear amp project. I have some radios that have a max of 30-40watts and id like to make a legal limit amp for them. I have all the other bits and pieces figured out except for which tube/ tubes to use. Im looking for a tube with a decent price and is readely available that can provide that kind of power. I was also looking to use GM3SEK’s controle board which can be used on either a triode or a tetrode. Amp will be used for 1.5mhz to 30mhz. Might even go to 50mhz while im at it. I have looked online at designs but id rather have other hams opinions. Any and all suggestions are much appreciated. Thanks AC8WP

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 17, 2016, 11:23:55 pm
content: GS35B?There's a very simple one described and even available in kit form athttp://f1frv.free.fr/Main costs are a safe HV setup and the cost of known good vacuum variables, but a tube is a lot more forgiving than a semiconductor

author: Jesset1996.5
author_rank: Regular Contributor
timestamp: November 18, 2016, 03:48:16 am
content: I could probably use 2 gs32b tubes. I was thinking of coppying this build.http://jetpropulsion.co.uk/gw0fzy-amateur-radio/gs35b-hf-linear-amplifier. It uses 1 gs32b but requires 85w drive to provide 900w. I could use 2 i guess and double the output with 30-40w drive.
bluetooth for Ham radios ? - Page 1
Forum section: electronics / rf-microwave

author: Flump
author_rank: Frequent Contributor
timestamp: October 25, 2016, 01:32:17 pm
content: I Use a 2m Handset on my Mobility Scooter but would like the speaker and microphone audioto be handled wirelessly using a headset, the PTT switch can be separate and wired.Does anyone know of a way of linking a bluetooth headset to the speaker audio& microphone audio so its full duplex ?I have found thesehttp://www.ebay.co.uk/itm/291619858437?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITbut cant see any reviews on the web yet and I would prefer the sound to be in both ears and not just 1.

author: Lord of nothing
author_rank: Super Contributor
timestamp: November 05, 2016, 01:07:02 pm
content: Does your Radio have BT?

author: Stephen37
author_rank: Contributor
timestamp: November 15, 2016, 09:15:56 pm
content: You could use any bluetooth headset, the best chip to search for ishttp://www.csr.com/products/csr8645(but it doesn't really matter for ham radio)However you need a special bluetooth interface for your radio if it does not have one, and here's the issue. A bluetooth module will transmit and receive at the same time only if it is set in headset or hands-free profile, and the only device that can do that is a cell phone or a custom device. Also, there is a catch because you would have to output and receive the ham radio's signals on the phone's headphone input/output.https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles#Hands-Free_Profile_.28HFP.29It's possible, but the main issue is software. In the past there have been bluetooth devices like the Jabra which converted an old phone to bluetooth and streamed directly back and forth. Nowadays that's not necessary unless one receives a call so one needs an application that is capable of setting the bluetooth headset in call mode and route the streams to the headphone output of a phone and with android that's not possible.So unless you have a raspberry pi or maybe an orange pi zero with a USB Bluetooth module & sound card and you are willing to kill a few of your neurons trying to route the sound from one to another in Linux it's pretty hard to make an interface for a ham radio.You could replace the raspberry pi or orange pi with a computer with either windows or Linux, but you still would have to write some software/configuration to do some magic and you could even replace the PTT switch with the accept call button on the headset.If you are lucky you can just play around in Windows with the Headset Profile and listen to the bluetooth microphone on the sound card and listen to the microphone or line-in of the computer with the speaker of the headset.Alternatively you can use an android/ios device to connect to a a radio remotely through the internet with an application that supports bluetooth headsets.
looking for good RF pcb factory in china. - Page 1
Forum section: electronics / rf-microwave

author: czorgormez
author_rank: Contributor
timestamp: October 21, 2016, 06:14:27 am
content: hii am looking for pcb manufacturer in china (preferably in shen-zhen) reliable and experienced with high frequency pcb. they all say they do Rf pcb and they fail. i need a factory who understand basic rf concepts and material use for high frequency. my project needs a different stack up than usual. (using 3 X 7628 prepregs)

author: KJDS
author_rank: Super Contributor
timestamp: October 21, 2016, 06:31:02 am
content: If you're wanting them made properly then you'll either need to be doing sufficient business with them to have your own QA employee supervising their production, or else you'll be better off getting them made somewhere else.

author: sanny
author_rank: Newbie
timestamp: November 09, 2016, 03:36:22 am
content: a very small amount irresponsible factory and suppliers damage the image of Chinese company , but do the vast majority of companies are conscientious in fact. This situation not only in China, but also exist in other area.

author: XFDDesign
author_rank: Frequent Contributor
timestamp: November 14, 2016, 02:30:58 pm
content: Quote from: sanny on November 09, 2016, 03:36:22 amI've been fond of GoldPhoenix PCB, but what you might be running into is the fact that these people are not RF Design Engineers, they're PCB manufacturers. For example, what band are you looking to operate on? The answer to this question is going to eliminate some vendors right there, as they might not offer the substrate you need. What kind of transmission line are you doing? Your substrate will have an impact on this. In the larger companies, usually we actually do our own characterization of the PCB vendor's materials, domestic or foreign. Where the cheap-as-chips Chinese shops fail is in the lack of consistency in substrate sourcing, which can lead to erratic spreads of Dielectric constants from board-to-board, and lowers your yield.

author: coppice
author_rank: Super Contributor
timestamp: November 14, 2016, 02:44:15 pm
content: Quote from: sanny on November 09, 2016, 03:36:22 amMost are pretty good these days, but there aren't many with deep experience of doing RF work.
Controlled impedance or RF PCB prototype supplier? - Page 1
Forum section: electronics / rf-microwave

author: dcarr
author_rank: Regular Contributor
timestamp: November 04, 2016, 07:54:03 pm
content: Hi all,I've been doing some design work near 10GHz recently and I'm looking for a prototype supplier that can supply PCBs with relatively well known Er (low loss is a bonus). Cost is a factor because I'm just doing this for fun. Homebrew isn't an option because I need lots of small plated holes (coplanar waveguide and QFN paddles).Does anyone know of a PCB house that either uses FR4 with a tight Er range or alternately does "RF-type" materials at reasonable prices (say <$50 for 2"x2")?FWIW - I've tried OSH Park but their FR4 Er spec is something like 4.0-5.4 which is too wide for repeatable results and the parts cost per board (~$100) is too high for me to risk willy-nilly.Thanks,David

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 05, 2016, 04:20:43 am
content: Cut it yourself by hand.You're looking at professional services starting around $500, I would guess. If you can't swing that, well...Tim

author: KJDS
author_rank: Super Contributor
timestamp: November 05, 2016, 03:51:07 pm
content: Isola are my go to manufacturer of good FR4. Far better performance than standard without the costs of Rogers or Taconic materials.

author: tggzzz
author_rank: Super Contributor
timestamp: November 05, 2016, 04:30:09 pm
content: Woven PCBs, e.g. FR4, have the disadvantage that the impedance can depend on the position of the weave relative to the track (both horizontally and vertically). There are mitigations, but how effective are they at 10GHz?

author: nctnico
author_rank: Super Contributor
timestamp: November 05, 2016, 06:46:19 pm
content: How about just ordering some boards and measure the Er? Overall an Er of 4.5 has led to good results for me but you can vary the board thickness to reduce the influence the Er of FR4 has versus trace width variations due to etching. Also the weave patterns can have an influence but it depends on your circuit whether this is a problem or not.At 10GHz there will be losses due to the FR4 material so I recommend simulating the critical parts of the layout with a simulator (like Sonnet) first.

author: rfbroadband
author_rank: Unknown
timestamp: November 05, 2016, 08:22:46 pm
content: EuroCircuits has an RF Pool that offers for example:2 layers2 x 2 inch0.5mm thicknesssolder mask: green, legend : white35$ / pcb using I-Tera43.55$ / pcb using Rogers 4350for this example I used 5 PCBs totalgo the websitehttp://be.eurocircuits.com/shop/orders/configurator.aspxand use their online calculator for immediate pricing information.

author: eb4fbz
author_rank: Regular Contributor
timestamp: November 07, 2016, 12:18:36 pm
content: PCBCart works with some high frequency laminates:http://www.pcbcart.com/product/high-frequency-pcb.html
Signal comparator/converter circuit - Page 1
Forum section: electronics / rf-microwave

author: Dajgoro
author_rank: Frequent Contributor
timestamp: November 01, 2016, 05:41:45 pm
content: Hi.I have a old vacuum tube RF signal generator which works, but the output amplitude is a bit attenuated.I remember some time ago on one of Dave's video he had shown some little board that can receive a signal of any amplitude and turn it into a square/clock output.Does anyone know what was that board, or if there is something similar which can be bought/built without too much hassle?
Looking for a radio powered by replaceable lithium-ion 18650 batteries. - Page 1
Forum section: electronics / rf-microwave

author: nbritton
author_rank: Frequent Contributor
timestamp: October 27, 2016, 05:02:10 am
content: I'm looking for a radio that is powered by user replaceable 18650 lithium-ion rechargeable batteries. I have a sizable cache of 18650 batteries and associated charging equipment, I would like to find equipment that can take advantage of these batteries. I'm primarily interested in handheld transceivers for use in emergency situations, but I'm interested in knowing more about any type of radio that takes 18650 batteries.The only radio I know of at the moment which takes 18650 batteries is the Tecsun PL-880.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 29, 2016, 12:48:39 pm
content: Hmm. So I'm guessing by the silence and the lack of search hits on google means these things just don't exist yet. This is a shame because the 18650 is probably the most common battery type in the world, practically every rechargeable lithium-ion battery pack uses these cells.How about a radio that can be recharged via a 5V USB port? Or 12 VDC?Alternatively, below is the battery bank that I own, it supports 3.6V, 5V, 6V, 9V, 12V, 15V, 16V, 19V, or 21V.https://www.aliexpress.com/item/3-6V-5V-6V-9V-12V-15V-16V-19V-21V-output-mobile-notebook-power-bank-box/32236605150.html?spm=2114.13010608.0.0.1oM74Q
Auto fuse to protect radio? - Page 1
Forum section: electronics / rf-microwave

author: w3amd
author_rank: Regular Contributor
timestamp: October 24, 2016, 07:30:07 pm
content: I just discovered this but it looks an auto fuse would be useless to protect a radio. You might as well use straight wire and hope for the best.Example:http://www.littelfuse.com/~/media/automotive/catalogs/littelfuse_fuseology.pdfor20A fuse rated at 100A in 1 second or 300A for 10ms.This would protect, NOTHING!

author: wkb
author_rank: Super Contributor
timestamp: October 24, 2016, 08:22:54 pm
content: Well.. it will prevent your car battery from boiling it's acid dry

author: Ian.M
author_rank: Super Contributor
timestamp: October 24, 2016, 08:41:14 pm
content: Fuses generally don't protect semiconductors because they are too slow. They are there to protect the wiring and reduce the risk of fire.

author: w3amd
author_rank: Regular Contributor
timestamp: October 25, 2016, 01:41:11 am
content: I guess that I'm trying to make the comparison between a fast acting more expensive fuse and the typical auto cartridge. There's a large difference in I^2T fuse blow time.I seen one YouTube with a 30A auto fuse on the input of a 100W Icom 7100. This fuse has even higher I^2R. Yes a 100W radio is going to have some current surges I'm sure. But 100W RMS is only 8A current @ 12.7V.From the one radio example where the entire board was wrecked the only fire prevention was the chips self destructing and UL94V ratings.Why would Icom put 30A fuse. This makes no sense to me. Even fire prevention could be questionable here.

author: dmills
author_rank: Super Contributor
timestamp: October 25, 2016, 01:47:31 pm
content: Well a 100W TPO radio will be somewhere around 40-50% efficient give or take, so maybe 16 - 20A or so at full snout, and if you are running RTTY or FM you are running full snout all the time the key is down.Of course SSB will be a fraction of that RMS, but still higher then you would expect as efficiency drops as you reduce the power, typically current falls as the square root of the fractional power.A 30A fuse on a rig that might hit 20A seems quite appropriate to me, I would probably even be ok with a 40A part, but 30A is a more common automotive part.In an automotive application wire size is far more typically limited by voltage drop then current rating, so while the fuse will not protect the rig, that is not its function, it is there to stop a car fire if there is a short circuit.Even the **EXPENSIVE** 'FF' semiconductor protection fuses only sometimes manage to fully protect the semiconductor, and those semis are typically huge geometry IGBT or Thristor parts not RF power sand with multiple emitter bond wires just waiting the blow open.73 Dan.
Vivaldi antenna  - Page 1
Forum section: electronics / rf-microwave

author: MrOmnos
author_rank: Frequent Contributor
timestamp: October 22, 2016, 02:42:00 pm
content: I need a couple of a couple of vivaldi antennas for my RADAR project. I need it to operate in ISM band and something that I can etch at home on FR-4 board. I am thinking of single clad notch element with coaxial line feed. Does anyone have any printable files as per my requirement? If not What software can I use to design one? I tried using kicad but it was a lot of hassle getting the exact shape and dimension.

author: LukeW
author_rank: Frequent Contributor
timestamp: October 23, 2016, 11:23:00 am
content: What frequency are you working with?I know this does not answer the question you actually asked about DIY artwork, but these ones for sale look nice.http://www.wa5vjb.com/products.html

author: Ammar
author_rank: Regular Contributor
timestamp: October 24, 2016, 10:56:46 pm
content: Most CAD softwares allow you to export gerber files if that is what you after.I once made an antenna by sticking pieces of duct tape on FR4 and etching with Ferric Chloride.
DDS controlled phasing method direct conversion receiver - Page 1
Forum section: electronics / rf-microwave

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: October 23, 2016, 07:28:03 am
content: A video describing and demonstrating a receiver covering 2 - 8 MHz AM/SSB/CWUses a direct digital synthesiser and the phasing method to (partially) null out the opposite sideband responseOnly the audio amplifier stages have a lot of discrete parts

author: German_EE
author_rank: Super Contributor
timestamp: October 23, 2016, 11:11:01 am
content: Nice work! I'm guessing that the boards you used have either square or round pads at the bottom rather than the boards with strips of copper, these are quite happy up to low-VHF frequencies and the version with a copper ground plane on one side will go even further. As for your transformer filter, the capacitors may not be needed, I use these transformers in some of my circuits and their frequency response falls off at about 3.7 KHz due to the core material.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: October 23, 2016, 11:41:20 am
content: Quote from: German_EE on October 23, 2016, 11:11:01 amMost boards I use have no copper pads - just join it up underneath. Though it gets a bit tricky under the 74HC4053. I've played around with capacitor values and they definitely have an effect - the sharper the roll off the better.

author: Kalvin
author_rank: Super Contributor
timestamp: October 23, 2016, 02:36:50 pm
content: If one wants to tune into higher frequencies, some minor changes needs to be made:- The AD9850 DDS has limited output frequency in a range of 30MHz - 40MHz as you have stated in the video, limiting the maximum receiver frequency below 10MHz. However, the DDS will be driving the digital inputs of the 'HC4053, so the DDS outputs can also be digital. The ADF4350 / ADF4351 and similar parts like Si570 can output higher frequencies in 100Hz steps or even less. For the ADF4351 the minimum output frequency will be around 35MHz and for the Si570 the minimum frequency is around 10MHz, but a synchronous divider by 8 will take care of that quite easily so you can go down to 160m band (1.8MHz).- The analog switch like the 'HC4053 has its own limitations as the part is quite slow and the internal resistance is quite high. For the low frequencies the device works pretty well, as you have observed. For the higher frequencies one has to use faster analog switches. There are faster parts with less internal resistance: For example the FST3253 and similar analog switches can give much improved performance. The switching rate of the analog switch in the commutating/tayloe mixer needs to be four times the receiver frequency. For example for a 10m band (28MHz) the switching frequency needs to be around 4 x 28MHz = 112MHz, which is not usable with the 'HC4053 analog switches any more, but the FST3253 can still be switched using this frequency.It was a nice video you have made, thank you!
CCI Motorola EB104 HF Amp - Page 1
Forum section: electronics / rf-microwave

author: cncjerry
author_rank: Unknown
timestamp: October 19, 2016, 10:50:03 pm
content: Years ago I bought a CCI 600w amp kit based on the Motorola EB104. For a host of reasons, I just started building it after 11yrs. It took me almost a month to find the transistors that Tom Sowden had sent me in 2005. Having all the pieces now I am starting the board + copper spreader + heatsink. I have a complete CNC machine shop so I shouldn't have problems in the physical construction.I am looking for others that have build this amp. The main question I have is the replacement of T3 with a transmission line transformer (TLT). I can't find the TLT information though admittedly I've only done a cursory search. I've found some note on the TLT on eHam but no building instructions.The power supply looks easy and I plan to get a transformer either from Ameritron or there is a toroidal transformer company that has an off the self transformer that will work. I have a lot of computer grade caps, diodes, etc. I'll probably add a micro-based SWR monitoring and control system as well as automatic band switching for filters.Any pointers would be appreciated. Also, if others have been kicking around starting this project, I'll help them with the machining of the heatsinks and spreader.Thanks,Jerry

author: German_EE
author_rank: Super Contributor
timestamp: October 23, 2016, 11:19:02 am
content: You may find the following links of interest:http://www.eham.net/ehamforum/smf/index.php/topic,83561.0.htmlhttp://home.earthlink.net/%7Echristrask/Trask1to1IsolBalun.pdf73German_EE
The Elektromagnitnyy Pushka - don't try it at home - Page 1
Forum section: electronics / rf-microwave

author: zapta
author_rank: Super Contributor
timestamp: October 22, 2016, 03:40:51 pm
content: Hilarious

author: ChristofferB
author_rank: Frequent Contributor
timestamp: October 22, 2016, 04:38:39 pm
content: Jeez

author: wraper
author_rank: Unknown
timestamp: October 22, 2016, 05:17:10 pm
content: They proven that tinfoil hat actually can be useful.

author: rob77
author_rank: Super Contributor
timestamp: October 22, 2016, 06:05:30 pm
content: apparently fakebut kind of entertaining
VNA Calibration - Page 1
Forum section: electronics / rf-microwave

author: D3f1ant
author_rank: Frequent Contributor
timestamp: October 16, 2016, 11:02:44 pm
content: Is it better practice to calibrate a VNA at the port and use port extension, or calibrate at the end of the cable/probe?I've just designed in the murata MM8030-2610 (suggested elsewhere by Howardlong) and have just received the matching probe with SMA connector. While I wait for the board, is it worth the effort making a little VNA calibration pcb with Open Short and Load for the cable/probe and these tiny connectors?

author: KE5FX
author_rank: Super Contributor
timestamp: October 16, 2016, 11:22:00 pm
content: It's always best to calibrate as close to the DUT as you can. Port extensions assume the interconnects are flat Zo transmission lines, so you need to think carefully about when that assumption is "close enough" and when it's not. If you are using 11 GHz connectors you're more likely to fall into the latter category than the former.A homebrew load with 0402 or 0603 resistors (use two 100R parts rather than a single 49.9R) can actually perform quite well up to several GHz. Not to 11, though.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: October 17, 2016, 02:15:12 am
content: Thanks that's what I thought would be the case. Its in the sub to low ghz range and using these connectors because they are so small and as bonus switched. Hopefully this is easier than soldering coax to a pad.

author: G0HZU
author_rank: Super Contributor
timestamp: October 17, 2016, 10:28:02 pm
content: Yes, see below for a screenshot of a cheapo 50R load I made many years ago using a salvaged SMA connector and some SMD 100R resistors.I used this load as part of a homebrew SOLT kit for many years with my old 3GHz HP8714B VNA.I've measured it below using a newer VNA and a modern Agilent Ecal module.

author: Koen
author_rank: Frequent Contributor
timestamp: October 18, 2016, 12:14:23 am
content: Hey, I had the same question some months ago and indeed, following the forum advices by moving to these connectors and calibrating on the PCB directly made a huge difference. If you need to match something, check outhttp://www.atyune.com/Both made the operation a breeze.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: October 18, 2016, 08:26:26 am
content: Atyune is good, been using it a while and just got some extra libraries

author: Andrey_irk
author_rank: Regular Contributor
timestamp: October 21, 2016, 03:48:20 pm
content: Quote from: G0HZU on October 17, 2016, 10:28:02 pmNice results! Can you show us a photo of the load?
Interesting amplifiers - GSM 900/1800 MHz - Page 1
Forum section: electronics / rf-microwave

author: max-bit
author_rank: Frequent Contributor
timestamp: July 31, 2016, 07:44:18 am
content: I have recently bought interesting amplifiers - GSMUSHR-900 and USHR-1800They characterized by very good parameters.More on the page.http://www.rflab.pl/rflab_wp/wzmacniacze-gsm-ushr-900-1800/The parameters much better than many Chinese - amplifier

author: Lord of nothing
author_rank: Super Contributor
timestamp: October 17, 2016, 09:29:18 pm
content: even in Polant its illegal. I will visit your Country soon.
SAW filter input output interchangeablity? - Page 1
Forum section: electronics / rf-microwave

author: daqq
author_rank: Super Contributor
timestamp: September 28, 2016, 07:34:30 am
content: Hi guys,Assuming that a SAW filter has both input and output impedances equal, can it be assumed that the input and output are interchangeable? I'm measuring one now, and it seems so. Is this correct, or is there something I'm missing?Thanks,David

author: chota.sanjiv
author_rank: Contributor
timestamp: October 16, 2016, 09:37:53 pm
content: The impedance must be matched so as not to de-tune the freq, but I don't think it would work in opposite direction, it just cuts the frequencies in which we are not interested.

author: KE5FX
author_rank: Super Contributor
timestamp: October 16, 2016, 11:19:30 pm
content: It'll work fine in both directions.
Singer CMS-1 - Page 1
Forum section: electronics / rf-microwave

author: silverlego3
author_rank: Contributor
timestamp: October 17, 2016, 12:42:55 pm
content: Hello! Just a few days ago I picked up this beautiful piece of kit as I build my collection. I'm a wanna be ham and working to get my technician licence.As far as I can tell it works just fine and on frequency (as well as I can test anyway).Does anyone know anything about this company history? There is almost no information about them online, Luckily I got the full service manual and instruction manual with it.It does just about everything from RF generation to a simple spectrum analyzer.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: October 17, 2016, 06:57:51 pm
content: That's strange, I was convinced Singer only made sewing machines! But the logo font is identical, so I guess it must be them.Just did some reading. Singer aquired a lot of electronics companies in the 1960's, so it may be another company's gear re-badged.
Decent RF product manuals as reference - Page 1
Forum section: electronics / rf-microwave

author: setq
author_rank: Frequent Contributor
timestamp: October 16, 2016, 02:54:46 pm
content: I've traditionally used a combination of sources to learn about various things. Typically a textbook or two and technical manuals for products. Some examples of the latter being lots of old Heathkit manuals, the Tek 321 and 465 manuals, US army PRC-77 manual etc. These are fundamentally very well written and easy to read and you learn a lot from them.Can anyone recommend any more, particularly covering superhet design, SSB and antenna systems?
Non inductive resistor brand/series? - Page 1
Forum section: electronics / rf-microwave

author: setq
author_rank: Frequent Contributor
timestamp: October 13, 2016, 06:16:48 am
content: Is there a canonical low power line of non inductive resistors suitable for building stepped attenuators for 0-200MHz max 1/2W dissipation.Also same question for 50 ohm load/termination resistor up to 10W? Assuming caddock for this?

author: daqq
author_rank: Super Contributor
timestamp: October 14, 2016, 06:10:15 am
content: Vishay has some RF resistors. See:http://sk.farnell.com/rf-resistorsThough at 200MHz you should be OK with most of the standard SMD thick/thin film stuff I think.As to the load, well, seehttp://sk.farnell.com/johanson-manufacturing/tf010bb1l/thick-film-resistor-flanged-50/dp/1754938

author: setq
author_rank: Frequent Contributor
timestamp: October 14, 2016, 06:14:39 am
content: Excellent thanks for suggestions.
Shh! Turn off that microwave! - Page 1
Forum section: electronics / rf-microwave

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 04, 2016, 02:11:09 am
content: Tim

author: tec5c
author_rank: Frequent Contributor
timestamp: October 04, 2016, 02:56:18 am
content: Great find. Thanks for sharing

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 04, 2016, 05:43:04 am
content: I suggest everyone sub to Tom Scott's channel. Great presentation of various cool sciencey stuff.Tim

author: daqq
author_rank: Super Contributor
timestamp: October 04, 2016, 08:41:57 am
content: Nice, thanks!
Rogers PCB manufacturing? - Page 1
Forum section: electronics / rf-microwave

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: September 27, 2016, 08:11:12 pm
content: I ordered some Rogers 3003/3006 and Duroid samples, The company was really nice and sent me a ton of extra PCB material. I mainly wanted to test it out for a line of hairpin filters I thought might sell well considering the price of a mini circuits and saw filters at common frequency's (about 15 -20) dollars. The PCB material works well and really outshines FR4, does anyone know a PCB house where you can order smaller quantity's 5-20 pcbs at a reasonable price, and uses high frequency materials?

author: KE5FX
author_rank: Super Contributor
timestamp: September 27, 2016, 08:24:24 pm
content: Sunstone can handle Rogers, and they're very convenient to order from.Sounds like a very interesting project -- more BPF options are always welcome!
Circular polarized cantenna feed for dish for 1500-2000mhz - Page 1
Forum section: electronics / rf-microwave

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: September 21, 2016, 09:23:35 pm
content: I am not sure if I have this down right but... If I wanted to build cantenna dish feed, for l-band sat and not wifi would I do this...First off can diameter, I used this calculator. I entered 1700 for the freq and 120mm for diameter and it seems this is pretty ideal.http://www.changpuak.ch/electronics/cantenna.phpNow as far as length im not sure if this is a calculated factor I read the longer the better?Second doing the Left Hand Circulation I would install one probe at the bottom and one on the left hand side of the tube. Next I would use something like the coax phasing system used in a cross yagi in order to get the proper phasing?What about ditching the probes and just using something like a cloverleaf in the can? From what I understand you dont want a crazy hi gain antenna feeding a dish though if I am correct this will just cause a ton of side lobes?I also thought about feeding with a "cross fire" antenna the FPV people are using, should I use a wave guide for any feed antenna I choose? Im not going helical. This is a small 18 inch dish and is only going to give me 15-20db max at 21cm /L Band. Also Ive seen dual feeds but I dont see many details on how there made... If I wanted a wide band 1500-2000(1900mhz really) and a 290-1320 feed of the same dish how could I achieve that?This is my first work with a dish so im sorry if these are stupid questions, almost everything I have done has been vertically polarized except a patch.
Lab Have new member just come - Page 1
Forum section: electronics / rf-microwave

author: ebclr
author_rank: Super Contributor
timestamp: September 20, 2016, 02:40:24 pm
content: What are the useful accessories to buy

author: LaserSteve
author_rank: Super Contributor
timestamp: September 20, 2016, 03:46:40 pm
content: Many 3 and 10 dB Attenuators, I keep a 3 DB on my SA as a form of cheap protection at all times.A few TTL crystal clock oscillators to make harmonics for sanity checks. 1.0, 3.3, 5.0, and 10 Mhz are typical, unless you have the tracking generator, in which case you probably don't need the harmonics.I find a 50 ohm load to be useful for determining if that weak spike is a spur or a actual signal, by shorting the input with the load. Also pays to have 50 Ohm dummy loads if working with higher power or transmitters.A directional coupler (better yet a pair of them ) for the region of interest.A near field probe for the region of interest, can be home made.A 6" / 15 Cm collapsible whip antenna.As many as you can afford GOOD QUALITY Adapters between BNC/SMA/N for versatility. You'll find BNC cables much more fun to use then N cables unless your in a professional lab. Avoid adapters with internal coil springs, such as some low cost BNC "Tees".Lots of high quality short cables with various SMA, BNC, and N connectors.... Short cables are usually a better idea then using a lot of adapters.A few WA5VJB Log Periodic Antennas across the spectrum if you want to hunt signals in the far field.If you don't have a tracking generator, a PTS160 or PTS250 synthesizer with the front panel knobs is a blessing and cheap. If you have time to make a set of switches, a PTS160 without the knobs goes for cheap, using the rear panel programming.On my buy soon list is one of these:http://www.hsmicrowave.com/CMG.htmlSteve

author: tggzzz
author_rank: Super Contributor
timestamp: September 20, 2016, 03:50:24 pm
content: Sacrificial N-type connectors/adaptors semi-permanently attached to the SA, to save the SA's connectors from wear.If DC on the input is prohibited, a DC block.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 20, 2016, 05:17:52 pm
content: If your into lasers, microwave, RF preamps, a Bias Tee and or a DC block is darn useful, but you should get some practice in first.Steve