Hi Bud,
Back in about '73, or so, having just gotten licensed 2 years earlier, I was
"blessed" with my one & only visit from a representative of the Department
of Communications here (our FCC) due to one of those nasty little 6AH6
electronic T/R switches...
My 6T9 8-watt rig was wiping out a neighbour's TV set half a block away ---
and this, despite my use of a low pass filter.
Ever since that time I've always looked upon such devices with a jaundiced
eye...
~73~ Eddy VE3CUI - VE3XZ
----- Original Message -----
From: "W2RU - Bud Hippisley" <W2RU@frontiernet.net>
To: <amps@contesting.com>
Sent: Wednesday, February 22, 2006 10:04 PM
Subject: Re: [Amps] QSK
> Although I've used QSK from the very beginning of my on-air activities a
> half-century ago, and feel like I'm blindfolded if I don't have it, I've
> known many excellent operators who didn't use it. A prime example is
> W1AX (ex-W1JYH), who is one of the best operators I've ever had the
> privilege of meeting, and he never had QSK during the years that he and
> I operated the same contests. What he _did_ have, instead, was a foot
> switch-driven PTT line, a nimble foot, and the "smarts" to lift his foot
> frequently to make sure he wasn't "stepping on somebody" (so to speak).
>
> The technology of QSK is an interesting issue. As a young Novice I used
> a separate antenna for my receiver. It was vacuum tube equipment, of
> course, and my transmitter only ran 15 watts output, so I never had to
> worry about blowing out the front end of my receiver. In college I
> built up one of those 6AH6 units that went inside my transmitter, where
> it hung off the high impedance end of the plate tank circuit with a
> coaxial cable capacitive divider. One bonus with that setup is that you
> could (and still can) quickly tune your final by listening to the band
> noise in your receiver.
>
> When finances allowed, I bought a "pre-owned" Johnson TR Switch, and
> I've used those ever since. In fact, I have four of them here. About
> the only improvements I'd make to them today is to add a dB or two of
> gain on 10 meters, extend their "official" operating range down to 160
> meters, and redesign the power transformer to run a lot cooler. The
> 6BL7 inside is a pretty rugged tube. My antenna tuners and the natural
> selectivity of my dipoles and Yagis keep the out-of-band signal levels
> down low enough that I don't suffer from cross-mod or blocking problems.
>
> Early on, I had to modify all my HF gear to be able to run QSK. Whether
> Hallicrafters or Collins, the exciters needed to have an additional
> mixer keyed so that there was absolutely no feedthrough of mixed local
> oscillators during key up periods. In contrast, today's transceivers
> all handle QSK pretty well -- up to the 150 or 200-watt level, at least.
>
> Amplifiers are another story. Over the years I've modified every
> amplifier I've ever owned (Collins, Heath, Hallicrafters, Amp Supply,
> homebrew, etc.) with Zener-diode biasing schemes (sometimes keyed) to
> cut off the plate current during key up periods. This eliminates any
> shot noise or partition noise at the output of the amp where the vacuum
> tube TR switch input is connected, and has the side benefit of reducing
> heat generation when operating CW.
>
> I currently own an Amp Supply LK-550 with a factory vacuum relay QSK
> system installed but I've never used this built-in QSK hardware because:
> a. It would probably make too much mechanical noise for me; and
> b. The key line that has to run through the QSK circuit (to
> provide proper time sequencing of the amplifier vs. exciter) doesn't
> function when the key down voltage on the key line is a Vsat above
> ground. I haven't had time to rebuild the solid state outputs of my
> various el-keyers to offset their outputs to 0.0 volts or below; and
> c. There's no (easy) way to get the output of the el-keyer in my
> transceiver to the QSK system in the LK-550.
>
> Another factor for me is that I am totally opposed to keying any
> unnecessary relays at a CW rate except for the high speed relays in my
> transceivers that I can do nothing about. I know there are PIN-diode
> QSK boxes out there, but I've heard of too many failures in them to be
> interested -- yet.
>
> I think many folks avoid QSK today because of the economics. I have in
> the back of my head that adding a manufactured QSK option to most
> commercially available amplifiers is around $400 -- provided you can
> afford an amplifier that _has_ a QSK option available in the first
> place. My primary amplifier is a Heath SB-220, so I'd have to get an
> external QSK box that costs about as much as the amplifier itself is
worth.
>
> But the truth is -- if you feel competent making simple mods to the dc
> bias circuitry in your amplifier, you can have noiseless QSK for far
> less than the cost of a commercial QSK box or a new QSK-enabled amplifier.
>
> That's why I keep on truckin' with my vacuum tube TR switches. Johnson,
> B&W, Handbook 6AH6 -- doesn't matter, they all do a comparable job
> except I'm not real keen on having to separately bandswitch a TR switch,
> so there's no bandswitched B&W units here.
>
> Bud, W2RU
>
>
>
>
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