A well-designed amplifier QSK circuit should never allow hot-switching
of the amplifier's T/R relays under any circumstances. There are several
ways to accomplish this goal, none of them expensive or complicated. For
example, in my own QSK design (QST June 2015, expanded info at
http://www.w8zr.net/QSK), there are two modes of operation. The first is
"semi break-in", where the only control line to the amplifier is the
ordinary relay output from transceiver.
The other mode is "full break-in" which routes the keying line through
the amplifier's QSK-IN and QSK-OUT jacks before it reaches the
transceiver. In this mode, the amplifier is ready to receive RF before
the transceiver begins to transmit. In both modes, however, the
amplifier will not key up if RF is prematurely present at its input, and
all internal amplifier relay and bias sequencing is done properly.
For operators running semi break-in with any amplifier, whether QSK or
not, is it is necessary to set the transceiver's TX Delay menu setting
to give advance warning to the amplifier that RF will shortly be on its
way. For my design, the amp simply won't key up if this warning is too
short, so choosing the correct setting is easily done. The K3's default
setting of 8 mS is plenty long enough for most modern amplifiers. With
the Flex, shorter delays are possible and can be found by trial and
error. In the full break-in mode, it doesn't matter how fast or slow the
amp relays are, because there is never any possibility of hot-switching.
73,
Jim W8ZR
Consider, for example, the K3 and Flex 6000 series transceivers. The K3
defaults to an 8msec delay, through menu setting TX DLY, and is
djustable up to 20msec.
N7YK discovered...that his K3 was hot switching his homebrew QSK
amplifier. I repeated his measurements using a scope on my K3. Both
radios had the KSYN3A synthesizer upgrade, which apparently changed
things. I also measured a friend's K3 that did NOT have the KSYN3A
upgrade, and the results were quite different.
73,
Bob, N6TV
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