Rich says:
> Similarly, it needs to be able to stand at least 1550
>>volts reverse on the 'off' side of the switch.
>? I have never seen a PIN diode with that much piv.
No, neither have I - 1200 volts is the highest I've seen - but you can
series the things with equalising resistors. Not that such diodes are cheap.
>However, like it or not, QSK switching speed in the amplifier is
needed
>with modern radios, even if the radio is being operated on
push-to-talk
>SSB -- because modern radios begin producing RF in as little as 5mS
>after the PTT switch is pressed. If the amplifier's relay contacts are not
>fully closed when RF arrives, the contacts can not survive. .
I think you mean "the contacts can not survive - for very long!" I interlock
the bias switching on my amp so that the relay has to be over before the amp
goes into tx. With modern rigs, as Rich intimates, you are quite likely to
be close to trying hot switching at the input, but at 100 watts, there's a
better chance to get away with it - especially with speed up techniques and
suitable relays.
>? and then there is the matter of dealing with lightning
discharges in
>the neighborhood. I had a 5000v doorknob capacitor short from a
>lightning discharge that was over 1000m from my 160m antenna.
There's one of the best arguments going for tube amplifiers and a suitable
relay which is energised for receive. The lightning induced EMP has to be a
lot bigger to blast a tube even as small as 6146 rather than a solid state
rx front end. I lost the front end of my FT102 with lightning EMP in the
first year after I got it; with the antenna relay in the amp arranged
'energise to receive', it's lasted years. I'd be interested in knowing if
these new solid state amps provide switching to isolate the antenna when the
equipment is switched off. If not, then how do they get on with mid West
summer thunderstorms?
I guess the bottom line on this is:
Yes, it's possible. It's certainly not going to be as cheap as buying a
vacuum relay if you want to handle 1500 watts into a worst case VSWR, the
drive circuitry is not negligible, and its ability to stand any lightning
induced EMP is arguable - so you really want a relay on the antenna side to
provide isolation when the station is switched OFF. BUT it can be done. At
400 - 500 watts, it's a lot easier.
73
Peter G3RZP
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