Maybe I'm swimming against the tide here, but all this discussion
about speeding up or slowing down relays is missing the real
underlying point: Avoiding hot switching the amp relays on both going
to TX and returning to RX. The schemes I have seen so far only address
the turn-on issue, not the turn-off one.
This is not a problem of speed, it is a problem of proper sequencing.
What should take place is this.
When going to TX:
1. Key the amp relays, both of them (if separate relays are used for
input and output)
2.A few milliseconds later, key the transceiver.
When returning to RX:
1. Unkey the transceiver.
2. A few milliseconds later, unkey the amp relays.
Done correctly, you don't have to worry about relay speed because the
amp will never "see" any RF except when its relays are closed, thus no
hot switching. Likewise the transceiver will never see an open load
when transmitting. The relays could be as slow as molasses and the amp
and transceiver would still be protected
Easier said than done, however. I am trying to come up with a circuit
using only relays (no solid state logic), possibly using the relay's
own contacts to switch in or out a capacitor across the relay coil,
but I'm stymied so far. Some clever person out there will no doubt
find a way. Please let us know when you do.
73, Bill W6WRT
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