High frequency compensation of T/R relay

Discussion in 'Amateur Radio Amplifiers' started by K9FV, May 5, 2012.

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  1. K9FV

    K9FV Ham Member QRZ Page

    Hello all, I just found a new article by Owen Duffy (vk1od) on compensation of T/R relays.

    link: http://vk1od.net/transmissionline/concept/RelayComp/index.htm

    Owen has a great site with LOTS of good tech info there. He really helped me with designing my 6 meter amp - as did several other folks here. Once I got my amp past the testing stage I thought it was close, but the SWR thru the T/R relay (bypass) was a bit higher than desired. Owen made the suggestions in his article and boy did it work! I put a 15pF (didn't have the 12pF) cap across the relay to ground as shown in his article and the SWR in bypass mode dropped right down to not measurable.

    Owen has many more good articles on his site.

    I'd like to say "THANK YOU" again to Owen for all his help,

    73 de Ken H>
  2. K9FV

    K9FV Ham Member QRZ Page

    The link seems to be good after all - I saw the "....." in middle and didn't think it was good.

  3. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Thanks for passing that along he does have some good stuff up there. :)
  4. KM3F

    KM3F Ham Member QRZ Page

    Just this last winter I had gone through extensive testing doing the same thing at 70 cm with both a power amplifier and a recieve amplifier switching that power.
    The input and output matching can be greatly improved by these type methods on amplifier input and output RF paths.
    At 70cm I found that inductive reactance takes over from excess lead lengths that often can't be avoided working with an existing design and needs capacitive reactance to counter.
    A side effect to consider is often there is more insertion loss introduced so a balance needs to be considered between match and loss.
    Trying to get common relays to work higher in frequency even with improved matching often results in a noticable insertion loss.
    When that is the case, closely look for any signs of heating that could lead to distruction if substantial power is involved.
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