The E.F. Johnson and B&W "electronic" TR switches worked just fine.
Central 20A into three 4X250's. Worked all TV sets for five miles.
http://www.universal-radio.com/used/sold109.html
Alex wrote:
> 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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