[Amps] Relays

[jeremy-ca]

And they were guaranteed TVI generators as well. Good concept on paper, not 
so good in actual use.

Maybe with analog TV going the way of the dodo bird they can be used but 
what other neighboorhood problems will they cause? FM radio wasnt that 
popular back in the days of the Johnson (and others) TR switch either.

Carl
KM1H


----- Original Message ----- 
From: "Alex" <alexeban at gmail.com>
To: <d.cutter at ntlworld.com>; "'Kim Elmore'" <cw_de_n5op at sbcglobal.net>; 
"'amps'" <amps at contesting.com>
Sent: Wednesday, April 02, 2008 5:59 AM
Subject: Re: [Amps] Relays


> 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 at ntlworld.com [mailto:d.cutter at 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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