Someone needs to explain how the Alpha then is not "hot switched".
Bob,
The Alpha circuitry senses when RF is present at the input BNC connector in
relation to the arrival of the PPT key line and in/out relay closure -- or
in the case of the 86, 89, and 87A amps, the output state of the PIN diodes.
I have been using several Alpha amps over the years and not once have I
encountered a hot-switching issue with the PIN diode amps, nor with the
older "K logic" Alpha 77Dx. These are intelligent amplifiers.
My only hot-switching issue occurred when someone suggested using TX-OUT
from an Omni Six to the input of my old Alpha 70V. This scheme is posted on
the Alpha website but the problem is that TX OUT (at least on the Omni Six)
results in no delay of the RF envelope. That's why the keying loop is
really needed to handshake back to Tx EN. The amp keying system that Alpha
shows on their website should not be used. It may work with some amps like
the sophisticated Alpha 80 series, but for anything with lesser
intelligence -- find a better solution.
My Alpha 70V uses a relay accelerator circuit, but there is no intelligence
to monitor the previously-stated keying conditions. In that event,
hot-switching occurred when I used TX OUT by itself. The solution was to
modify the Omni's output by sensing the "T" voltage line. I have never uses
a key loop on my amps and have never needed one. I would rather correct the
timing issue where it matters most, and that's inside the transceiver. Of
course, I could have used the loud, slow amp relay in the Omni Six, but what
fun is that for a high-speed op?
The key loop structure used on some amps is generally not a tool to correct
for inadequacies of the amp. It's a tool to deal with inferior transceiver
designs. TX OUT should only be used with TX EN -- not by itself unless a
scope is used to ensure that an amp is not hot-switching.
Paul, W9AC
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