[TenTec] QSK switching diodes in Scout

[Al Gulseth]

Clifton Labs has a writeup which might be of interest in this regard:

<snip> It's commonly understood that the 1N4007 has an special junction 
structure resembling a PIN diode and it has, of course, been widely used as 
a "poor man's PIN diode" in RF power switching. Elecraft, for example, uses 
1N4007 diodes for transmit/receive switching in both its 10 watt and 100 watt 
option K2 transceiver.

Used as a quasi-PIN diode for RF power switching, the 1N4007 takes advantage 
of the lengthy reverse recovery period, which prevents it from rectifying the 
high frequency signal it is switching. (This is because the reverse voltage 
half-cycle period of, say, a 3.5 MHz signal is much shorter (140 ns) than the 
reverse recovery time. Hence, if forward biased with DC, any reverse bias 
from RF negative half-cycles don't last long enough to neutralize the 
1N4007's excess minority carriers. Hence, the 1N4007 stays forward biased and 
presents a low impedance to the full RF cycle. There's a minimum frequency 
for this effect which we see from the trace below. With a bias current in the 
60 mA range from the 8012B pulse generator, we see the following voltage 
waveform. <snip>

http://www.cliftonlaboratories.com/diode_turn-on_time.htm

73, Al

On Mon May 16 2016 8:59:45 pm Gary J FollettDukes HiFi wrote:
> Interesting, i did not know that!
>
> Thanks!
>
> > On May 16, 2016, at 6:28 PM, Stuart Rohre <rohre at arlut.utexas.edu> wrote:
> >
> > The silicon diodes signal path in the Scout are made with die similar to
> > PIN diodes, or identical.
> >
> > -Stuart Rohre
> > K5KVH
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