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, 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.
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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