[Amps] Relays

[Alex]

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

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Kim Elmore
Sent: Wednesday, April 02, 2008 4:48 AM
To: amps
Subject: Re: [Amps] Relays

Thanks, Vic!  Makes perfect sense. Yes, the PIN diodes are quite 
expensive, especially for ones capable of handling much power.

73,

Kim N5OP
At 06:28 PM 4/1/2008, you wrote:
>Kim Elmore wrote:
>
> > But, this does lead to a question: are PIN diodes avoided simply
> > because using them is far more complex than relays, or is there some
> > other reason they aren't often used?
>
>The cost of the diodes and associated circuitry is more than a cheap
>relay. And they are susceptible to damage from lightning-created
transients.
>
>I had an Alpha 86 with pin-diode switching that worked great. Never any
>problems. But a lot of Alpha users did have problems and at some point
>they started using vacuum relays. Someone who can afford a newer Alpha
>can tell us if they still do!
>--
>73,
>Vic, K2VCO
>Fresno CA
>http://www.qsl.net/k2vco
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