OH, YEAH!
Back in the sixties the radio Bible carried for years a T/R switch based on
a triode. It was based on the principle of grid leak bias i.e. the RF
developed bias for the tube to cut it of and thereby divorce the radio from
the antenna during transmission.
If I can find the schematic I'll scan and post it.
73, Alex
-----Original Message-----
From: d.cutter@ntlworld.com [mailto:d.cutter@ntlworld.com]
Sent: Wednesday, April 02, 2008 12:31 PM
To: Alex; 'Kim Elmore'; 'amps'
Subject: Re: Re: [Amps] Relays
Back in the days of steam radio, didn't we use TR switching using bottles?
I seem to remember an 807 used as a switch, but the memory dims and I'm not
next to my library to look it up. Do we *have* to detach the PA on receive?
Perhaps there's a way without resorting to PIN diodes, but then, someone
would have thought of it already.
David
G3UNA
> >
> Hi guys:
> It so happens that during the last 2 years or so I worked on high power
> amplifiers in the kilowatt range .
> PIN diodes are made by very few manufacturers, coming and going all the
> time. They can run In the 300$ dollars range, are susceptible to burn out
at
> mediocre SWR,s and require back bias voltage approximately 3 times the PTP
> RF voltage involved. They also require a forward current of a few hundreds
> of mA to conduct well when open. This adds directly to the input noise
> because they operate as a noise diode would.
> In short, if you don't need fast switching speeds, don't mess with them.
> They also have only a poor isolation of around 30 dB. In QRO use the
> leftover power at the receiver port is still to much so that you need some
> additional switching after the main diode with associated driving
circuits.
> In short, drop it!!!
> 73 and all the best:
> Alex 4Z5KS
>
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