swr bridge re use+ repair - Page 1
Forum section: electronics / rf-microwave

author: p.larner
author_rank: Frequent Contributor
timestamp: January 18, 2024, 02:33:22 pm
content: I have the swr bridge/coupler pcb from an old yaesu fl-2100z linear,it has the detector diodes open circuit,firstly can i use 1N5711 diodes for replacements,also this was originaly on the antenna side of the linear,can i use this in a atu low to medium power say 25w max?.

author: A.Z.
author_rank: Super Contributor
timestamp: January 18, 2024, 03:38:33 pm
content: So, basically you have the PB-2056A board from the FL-2100Z and you found that the diodes were damaged ?In such a case you'd better use a couple of diodes matching the characteristics of the original 1SS97 oneshttps://datasheetspdf.com/pdf-file/788831/NEC/1SS97/1but then, you'd better check the other components on the board, since they may be damaged as well, at that point you may add the metering circuit and use a known good meter to adjust the measurement, notice that nothing forbids you to connect two instruments to the board and have fwd and ref measurements at the same time

author: p.larner
author_rank: Frequent Contributor
timestamp: January 18, 2024, 04:19:34 pm
content: i just wanted to know if the 1n5711 diodes would work?,also it looks like the torroid coil in the schematic has a center tap going to c+r 21,mine doesent look like its tapped,just 1 wire thru its center and the coil wound around the core without a tap as far as i can see looking at the pcb,any ideas?.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 18, 2024, 08:22:30 pm
content: Quote from: p.larner on January 18, 2024, 04:19:34 pmDefine what you mean by work? Will your diode rectify AD to DC to drive a meter, sure, any old diode will do that. Is your diode a drop in replacement that will not require calibration, absolutely not. Just check the datasheet for your diode to ensure it will deal with the voltages and do some quick calculations to make sure that the directional coupler is wound to deal with your power levels. You want to run at say 50W, but if this came out of a 1KW rated amp, its winding ratios will be all wrong and you wont have enough voltage to overcome the forward bias drop of your diodes.You are just going to have to do some math. The actual diode you use, seems to me to be the least of the problems with repurposing this. The thing to remember with a SWR meter, its all about the meter rating really, you start with it and work backwards. Say you have a 50ma meter, you design all the rest to give a 50ma deflection at the highest input rf power.

author: A.Z.
author_rank: Super Contributor
timestamp: January 18, 2024, 09:04:26 pm
content: a savy man once said"never argue with an idiot, he'll drag you down to his level and beat you through experience"now check the post history for the OP and make yourself an educated opinion.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 18, 2024, 09:31:23 pm
content: Quote from: A.Z. on January 18, 2024, 09:04:26 pmThen don't argue or debate with him. Just present the facts. Will this diode work? Yes it will, But....reasons. I am not doing the math and design work to ensure its fine, that is all on him. Just point in the right direction and leave it be. I am a home brewer, respect to anyone that is giving it a go, even the rude little men who cant say thanks. I came to the realization a long time ago than ham radio is filled with autists and other assorted social retards, so I have pretty low expectations to begin with. But its still better to offer basic facts than offer nothing at all.Hopefully someone else finds this thread and the information contained in it useful.

author: A.Z.
author_rank: Super Contributor
timestamp: January 18, 2024, 10:21:08 pm
content: roger to it, out and over.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 19, 2024, 01:59:13 am
content: can you say why the schematic shows a center tapped torroid but my original pcb has no tap?.thanks.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 19, 2024, 02:36:25 am
content: Quote from: p.larner on January 19, 2024, 01:59:13 amAre you sure your pcb wasn't pulled out of a FL-2100B?

author: p.larner
author_rank: Frequent Contributor
timestamp: January 19, 2024, 10:28:51 am
content: its funny you say that as the amp doesent have the warc bands but the front pannel switches are deffinatly for a 2100z,did they make an inbetween model,would knowing the serial number help?.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 19, 2024, 10:34:29 am
content: just looked mine has the multi position rotary switches for meters+swr call,not the rocker type like the "B" model,its odd.73

author: A.Z.
author_rank: Super Contributor
timestamp: January 19, 2024, 01:55:31 pm
content: Quote from: p.larner on January 19, 2024, 10:34:29 am@p.larnerA question, if I may; do you have around a couple of dual gang air variables with a max capacity of about 365pF or 500pF ?

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 19, 2024, 09:42:54 pm
content: Quote from: p.larner on January 19, 2024, 10:34:29 amThere is a fair chance what you are looking at was modified by someone back in the day. Seeing you are only concerned with repurposing the SWR meter portion, you do not have a lot of circuit to draw out and work out what is what.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 19, 2024, 10:01:34 pm
content: once againe whats with the torroid center tap on the schematic tht my pcb doesent have,ive never seen a torroid used for sampling swr with a center tap,is it common?

author: Andy Chee
author_rank: Super Contributor
timestamp: January 20, 2024, 05:54:03 am
content: I wouldn't say it's common, but I wouldn't say it's unique either.If I had to guesstimate a percentage of SWR coupler designs, I'd say 25-30% use this technique.It's just a different way to skin a cat.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 22, 2024, 10:37:28 pm
content: in answer to the fella who wants to know if i have variable caps,theres a few kicking around in my junkbox,its an odd question,the reason i asked about using 1n5711 diodes is there all i have apart from some old unmarked mullard germainium point contact diodes,i wasnt sure what to use,the originals are o/c and the r2 resistor is cooked with most of its body missing,looks like the amp had a hard time at some point,i brought it from peter roddmel from linear amp uk,brought it for just the transformer for a project and decided it was worth rebuilding,it had missing psu caps no valves and the plate load cap busted as well as a fried bandswitch wafer and all the hv caps missing,it then worked and if driven would output about 800+watts,i had a fright when i saw its power consumption,it was like keying up a 3bar electric fire!,just been sat doing nothing since,i never did get around to wireing up the swr meter so didnt know the bridge was busted 73.

author: A.Z.
author_rank: Super Contributor
timestamp: January 23, 2024, 08:10:46 am
content: Quote from: p.larner on January 22, 2024, 10:37:28 pmNot so odd, you opened a gazillion threads, first regarding your "doublet" antenna, then about ab attempt to wind a balun, then about an attempt to build an antenna matching unit and then, again, about a directional coupler, now since all those discussions are related, I was curious to know if you have some DUAL GANG air variable capacitors, even the type used in old radios will do, as long as they have a max capacity (per gang) of 350...550pF, do you have a pair of those around ?

author: p.larner
author_rank: Frequent Contributor
timestamp: January 23, 2024, 08:17:28 am
content: yes i have plenty of caps,before you ask,ive built an l match atu thats working great,its just the metering that i need too finish.

author: A.Z.
author_rank: Super Contributor
timestamp: January 23, 2024, 06:26:47 pm
content: Quote from: p.larner on January 23, 2024, 08:17:28 amstrange, last time you wrote you were about to dismantle it since it wasn't working ok...anyhow, if it works and you like fiddling with the roller coil and with switches, fine with me <g>

author: p.larner
author_rank: Frequent Contributor
timestamp: January 24, 2024, 07:31:30 am
content: yes i had to strip it as the turns counter stopped working,was a pig due to corrosion,lots of stuff sheared off,spent about 5hrs on the roller it had a lot of issues due to age,i have a homebrew t match as well,that also works well,with the lmatch,it was ok on 80+40m but didnt work on higher bands,it was a 1000pf cap so had too much min c,ive removed 2/3 of the plates ish,and switch in 1400pf of silver mica padding caps for the lower bands,as i said its just the metering to finish,i have the bridge for that now nearly finished,just the power range adjustment pots and switch to fit,should be ready for testing later today 73.

author: A.Z.
author_rank: Super Contributor
timestamp: January 24, 2024, 09:42:41 am
content: Quote from: p.larner on January 24, 2024, 07:31:30 amI see, as I wrote if you are ok fiddling with roller coil and/or "band select" switches, then fine with me, but there are other antenna matching networks around than the T or L, and some which don't require switching, just adjusting two capacitors, nothing else, an examplehttp://dl4cs.de/funktechnik/ant/fri-match/en.htmthe only switches there are the bypass one and the second which allows to "flip" the circuit to deal with low or high Z, depending from the band, no complex wiring or special stuff, further examples and infos can be foundhereandheregetting back on topic, a good coupler schematic can be found herehttps://vk8rhradioprojects.com/power-swr-meter/along with infos about the windings, the dots in the above schematic show how to wind the coils around the toroids and the URL above gives informations about the number of turns to use which mostly depend from the desired attenuation, nothing special, no rocket science

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 25, 2024, 07:30:41 am
content: Quote from: A.Z. on January 24, 2024, 09:42:41 amI would not trust those dots as fact. They are an artifact of LTspice and how you orientate the part in the schematic. there is way to much assumption that the author was right or knows what they are talking about. I cant find any decent textbook with anything in it to confirm or deny anything.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 25, 2024, 11:06:33 am
content: well i have made this(see pdf),i have my rig going into the 50 ohm in as marked on the pdf,the 50 ohm out goes to my daiwa swr meter and then into my atu,if i tune say 80m and then insert the pcb from the pdf the swr goes nuts,as soon as i remove it its fine,i need to work out what goes,the only thing is ive used 1n5711 detector diodes and unknown torroid cores from my junkbox,i am off too a radio rally pn sunday so will buy some 43 mix torroids.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 26, 2024, 09:16:59 am
content: well i made this and fitted it between my atu and existing swr meter,if i tune my antenna to read 1-1 when i fit the new coupler my existing swr meter goes from reading 1-1 to over 3-1,would having the wrong torroids cause that?,i hope tht make sense?.its the cct in my attatched pdf i built.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 27, 2024, 01:57:26 am
content: Quote from: p.larner on January 26, 2024, 09:16:59 amYou cant have 2 swr meters in series. they will affect each other.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 27, 2024, 04:03:11 am
content: why is that,as i said could the wrong torroids cause this?

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 27, 2024, 09:32:14 pm
content: Quote from: p.larner on January 27, 2024, 04:03:11 amWithout greater information, pictures and other such tests, my gut says user error in the build. You have a VNA, do an S21 on both SWR meters and see what is what from 1 to 30mhz. An swr meter is essentially a pass though as far as anything connected to it is concerned, it should be invisible and not add any load to the system. Grab a stack of 3 or 4 of these riods you used and pass them over an sma patch cable and put them on the VNA for an S21.Without data we can only offer advice, with hard data we can look over your build for obvious errors, I cant see how the torriods can be placing such a load into the system. It should be just a single wire passing though the center, its not adding and tranformative effects, a poor choice of material will effect how accurate its measurements will be over frequency, becoming poorer at higher frequencies.Here's one i prepared earlier. Your S21 should look something like the image below.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 27, 2024, 09:49:27 pm
content: Quote from: p.larner on January 27, 2024, 04:03:11 amHere is a random green ferret, well no so random, i use these for other things,its a little more lossy than other ferret mixes, but would be suitable for HFThis is a type 43 mix sleeve, a little less lossy across HFSo, if the pass through of your SWR meter does not look like any of the above plots, you did something wrong and if the ferrite mix you used does not present a rather flat S21 from 1 to 30mhz, then they are useless for the task. Post some pictures, lets see what you have going on.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 28, 2024, 07:07:34 am
content: would you have the artwork to the bridge shown so i can etch one?.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: January 28, 2024, 10:23:27 pm
content: Quote from: p.larner on January 28, 2024, 07:07:34 amI am not sure that the 50ohm resistors I used are commonly available, or the huge binocular, it was made with what crap I had here in mind, not actual repeatability. It based off the schematic by Diz at Kits and Parts, beafed up to take 200w continious. He sells a complete kit for 12 bucks and a bare PCB for 4 bucks. Pretty sure there are chinese clones of this on ebay as well for very little money.I can teach you how to layout a pcb and have it sent off to china for making. 5 pcb 100x100mm cost like 5 bucks delivered.

author: p.larner
author_rank: Frequent Contributor
timestamp: February 02, 2024, 09:46:00 am
content: how many turns doe T1+ T2 have on there secondarys?.

author: VK2AZT
author_rank: Newbie
timestamp: February 02, 2024, 08:27:36 pm
content: The diagram shows that the secondaries take 10 turns. No idea what gauge wire is used but a thin diameter would be best.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: February 03, 2024, 12:20:10 am
content: Quote from: p.larner on February 02, 2024, 09:46:00 amIt depends on the amount of power you are driving though it and the ma rating of the meters you are using. For mine, its designed so that the tapped off voltage is a maximum of 5V at 200W as the maximum input voltage to the ADC i am using is 5V.But if you are using physical meters, you want the turns ratio to give you the maximum defection at the highest power the meter will see. As designed in the schematic, its 10 turns for 5W continuous with 50ma meters. Which should be fine for 50 to 100w with appropriately rated 50ohm resistors.

author: A.Z.
author_rank: Super Contributor
timestamp: February 03, 2024, 07:55:03 am
content: well the ratio also affects the min measurable power btw

author: p.larner
author_rank: Frequent Contributor
timestamp: February 03, 2024, 09:53:39 am
content: Quote from: vk4ffab on February 03, 2024, 12:20:10 am

author: p.larner
author_rank: Frequent Contributor
timestamp: February 03, 2024, 07:34:16 pm
content: well i rebuilt this coupler(see pdf),the first attempt was using unknown torroid cores,this made the swr rea 3+ when inline between my swr meter and atu,i was going to try and get some 43 torroids from a rally on sunday but there was none there,i got 10x ft-50 43 mix torroids from ebay,now its working ok,73.

author: A.Z.
author_rank: Super Contributor
timestamp: February 04, 2024, 02:03:41 pm
content: I believe the main issue is the fact that you're using torroids, while any other uses toroids

author: p.larner
author_rank: Frequent Contributor
timestamp: February 04, 2024, 05:25:39 pm
content: does the lh side go to the rig or rh side on the pcb,all it says is 50 ohm in 50 ohm out,is it the same convention,ie power input from the left?,i am unsure how to connect it,thanks in advance for a basic question.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: February 04, 2024, 09:33:09 pm
content: Quote from: p.larner on February 04, 2024, 05:25:39 pmWithout looking at your schematic, or how you built the bridge, there is an input side and an output side in relation to the meter display, you can reverse the input and output and it will reverse the meter movements, IE FWD becomes REV. So even if its unmarked in your document, you can determine experimentally which is which.

author: p.larner
author_rank: Frequent Contributor
timestamp: February 04, 2024, 11:49:48 pm
content: this is what i built see pf,its to fit inside an atu,i dont want to have to rewire it once in,hence need to know what side goes to the rig,all it says on the pf is 50 ohm in 50 ohm out,!.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: February 05, 2024, 08:56:06 am
content: Quote from: p.larner on February 04, 2024, 11:49:48 pmTake a look at your linked file again, its all in there in one of the diagrams. Big labels saying IN and OUT.

author: p.larner
author_rank: Frequent Contributor
timestamp: February 05, 2024, 09:55:31 am
content: i see the in and out but is in from the rig or antenna,its confusing.

author: A.Z.
author_rank: Super Contributor
timestamp: February 05, 2024, 07:49:02 pm
content: so long, and may we never meet again.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: February 06, 2024, 04:48:46 am
content: Quote from: p.larner on February 05, 2024, 09:55:31 amNo idea, but, if you think of input and output as in which way the RF travels through the device while making a measurement, In and Out then make sense. Power travels from the transmitter through the device to the antenna you are trying to measure.