The main point about the PIN diode is that you need a long carrier life time -
5 to 10 microseconds is good for 160m and up. I STRONGLY recommend reading the
application notes at Microsemi.com - that tells you nearly all you need to know
about PIN diodes and their applications.
I have used 1N4007s as PIN diodes, but you need to be a bit careful on the
manufacturer, because some of them are faster than others, and as a result,
don't 'PIN' too well. I found that they weren't too reliable long term at 100
watts, though. Bigger power rectifiers could well be quite good, although the
problem then is the 'OFF' capacitance of the device.
The principle of the PIN is that because of the long carrier lifetime, when the
RF signal reverses polarity, the current keeps flowing - that's why there's a
lower frequency limit.
I have some devices for 'one day use', rated at 1 amp forward current, 2kV
reverse volts, stud mounted and about 10 microsecond carrier lifetime. One
day.....I hesitate a bit, because I prefer to arrange the amplifier so that
when in receive, the antenna relay is actuated. This means that when the
station is off, any lightning induced surges down the coax go to a high voltage
rated device - the tube - and hopefully not into the rx front end. Remember
that lightning over here is a LOT less severe than you get in the US......
73
Peter G3RZP
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