If you want to handle the worst case of an infinite VSWR at 1500 watts, then
your PIN diode switch needs to handle 15.5 amps peak of RF at the lowest
frequency in use. Similarly, it needs to be able to stand at least 1550
volts reverse on the 'off' side of the switch. For 'typical' HF diodes with
recovery times of 10 microseconds, this probably means about 4 amps forward
current [I don't have the equations with me here at work].
The drivers for this are not a negligible design problem...........neither
are getting the PINs.
I asked W2VJN of Top Ten Devices about this: he answered (paraphrasing) that
he felt that making a PIN switch that was ham proof would be too expensive.
I've got some 1000volt PINs that will take about 1 amp DC forward: I figure
they're good for about 1kW into 50 ohms. They'll stand an SWR of around 5:1,
I guess at 1kW, but I don't like pushing semiconductor devices to their
limit. Fortunately, if you accept a normal relay switching the antenna
around the amp, and have a separate rx antenna input to the transceiver (as
most Yaesu's do), the problem eases a lot - but you still need to watch that
SWR on tx.
Trouble is, having had full QSK, I don't like it anyway......
73
Peter G3RZP
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