Taking Off The Training Wheels

Discussion in 'Homebrew and Kit Projects' started by VK4FFAB, Apr 18, 2017.

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  1. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I've worked Don, also -- he's pretty local and very strong on 40CW in the late afternoons before the band stretches out.

    I read his writeup and didn't see anywhere he plotted switching vs. frequency other than to write "HF" and such. The spectrum analyzer captures are cool but I didn't see anywhere he defined the X axis for actual frequency.

    I don't think his switch using 1N4007s will work at 1.8 MHz. Of course, technically, that's not "HF," it's really "MF" (HF starts at 3 MHz), so this wouldn't be a correction to anything he wrote. But it would be interesting to test it all on 160m. My guess is: It won't work.
    AF6LJ and N2EY like this.
  2. N2EY

    N2EY Ham Member QRZ Page

    It was a great QSO - the Southgate Type 7 on my end and his all-homebrew rig on his end. Old and new technologies! And of course great CW - which is the only real reason to have QSK.

    1N4007s work OK in the Elecraft K2. (It covers 160 with an add-on option). Wayne and Eric have designed and built a few rigs........and they actually work.

    73 de Jim, N2EY
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    True, but the K2 is a 10W rig. I wonder if the "1N4007" QSK works on 160m?

    That's really been the obstacle in many PIN QSK circuits, even using real bona fide PIN diodes designed for that application. The majority are "microwave" PINs and carrier lifetime is too short to work below 3.5 MHz, so they tend to rectify at lower frequencies, add distortion, and get hot.

    My own SS QSK circuit uses parallel Unitrode/Microsemi UM400X series that have very long carrier lifetime and does work at 1.8 MHz with no ill effects, at 1500W key-down power. Bias switching doesn't use power FETs as Don did it, it uses a Mercury-wetted relay that's incredibly fast and can handle millions of cycles. FETs would have been cheaper.:p
    Last edited: Apr 19, 2017
  4. N2EY

    N2EY Ham Member QRZ Page

    Yes, it does.

    Of course there's a 100 watt option. You can check out the circuits on the website.

    Works for Elecraft.


    There's also the vacuum relay approach. But....if one operates CW a bit......you'd be surprised how quickly a million cycles adds up.

    in fact....

    Let's do the math!

    Say someone operates 30 wpm (a pretty moderate speed).

    The standard word "PARIS" has 15 operating cycles in it, so 1 minute works out to 450 operating cycles at 30 wpm. Times 60 minutes is 27,000 cycles per hour. Divide 1,000,000 cycles by 27,000 and you get.......37 hours!

    Of course in amateur operation one isn't transmitting all the time - say, 1/3 of the time. Now we're up to 111 hours. If the relay lasts 10 million cycles, that's 1,110 hours. Operating just 1 hour a day, that's about 3 years.

    73 de Jim, N2EY
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    My Mercury wetted (old C.P. Claire) relay in my QSK box was completed in 1989 and has been in almost continuous use since then.

    I'd estimate ~4 hours/week or actual "use" (since a lot of bench sitting is just receiving). That would be only about 5616 hours of use. At 27K cy/hr > 150 million operations! It still works.:p

    I don't actually recall what it was "rated" for, but I think around 30 million cycles or something. I've almost surely exceeded that.
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  6. VK4FFAB

    VK4FFAB Subscriber QRZ Page

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  7. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    What you are looking for in a switching diode...
    1. Low forward voltage (low on resistance)
    2. Low reverse capacitance. (for HF a few PF)
    3. Reverse voltage rating well above the peak RF voltage plus the maximum DC voltage used to cut off the diode.
    4. Forward current rating high enough to allow for the RF power under less than ideal conditions, like running into a less than desirable load.

    The reverse recovery time is not that important for an SSB or CW transceiver.
    VK4FFAB likes this.
  8. N2EY

    N2EY Ham Member QRZ Page

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  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

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  10. VK4FFAB

    VK4FFAB Subscriber QRZ Page

    Thanks everyone.

    Thanks Sue, that will help me evaluate things better.
    AF6LJ likes this.

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