[Amps] QSK (okay, not QSK...)

R.Measures r at somis.org
Sat Feb 25 15:52:13 EST 2006

On Feb 25, 2006, at 6:26 AM, Ian White GM3SEK wrote:

> R. Measures wrote:
>> In my experiences, an RJ-1A will not do 50wpm without a speedup 
>> circuit
>> to decrease its make time from c. 6mSec to 2mS.   see
>> http://www.somis.org/D-a-07B.jpg
> It all depends how much character distortion you're prepared to
> tolerate,

The problem is hotswitching, not distortion.

> given that one dot at 50wpm is 30ms long.
> Many transceivers cannot do full QSK at anywhere near 50wpm either. 
> This
> puts the squeeze on the amplifier designer, to avoid making a bad
> situation even worse.

As long as the amplifier can switch faster than the transceiver, there 
will be no hotwitching.
> The critical timing is when switching from RX to TX,  and the RF relay
> changeover isn't the only time delay involved. It's best not to switch
> the bias until *after* the relay has changed over and connected the 
> tube
> to a safe load. So you then need time to switch the bias and let the
> tube settle to its new DC operating condition. To  further reduce the
> risk of hot-switching or distortion of the keying waveshape from the
> transceiver, it would be prudent to add a safety margin of a few more
> milliseconds.
> Thus a 6ms delay in the relay can easily imply a total dead time of 
> like
> 10ms or even more - which is a very significant fraction of 30ms. If 
> 6ms
> can be reduced to 2ms, that would a very worthwhile improvement.
> Vacuum relays like the RJ-1A respond very well to speedup circuits that
> deliver a 'kick' of high current at switch on. Rich, Paul WD7S and I
> have all measured similar improvements.
> The speedup circuit I use was designed by K1KP and publicized by K6XX,
> and has the advantage that it works from the existing 24V rail. It also
> includes a fast PTT input that won't damage the solid-state PTT output
> of any transceiver.
> http://www.ifwtech.co.uk/g3sek/in-prac/best-of.htm#speedup
> -- 
> 73 from Ian GM3SEK
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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