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Re: [TowerTalk] Help need Vacuum Relay Isolation 1.8 to 30 MHz

To: "Tom Rauch" <w8ji@contesting.com>,"RCARIELLO" <RCARIELLO@si.rr.com>,"Towertalk" <Towertalk@contesting.com>
Subject: Re: [TowerTalk] Help need Vacuum Relay Isolation 1.8 to 30 MHz
From: "Jim Lux" <jimlux@earthlink.net>
Date: Tue, 4 Jan 2005 21:46:59 -0800
List-post: <mailto:towertalk@contesting.com>
> > At the 1500 watt power level will the single open vacuum
> relay provide
> > enough isolation?
>
> Sure. If it is a typical vacuum relay. I use them all the
> time even in 25 kW and higher systems.

Are you thinking front end burnout, or same band isolation?

>
> > How much isolation can I expect?
>
> 60 dB or more if you do a good layout.

Even though the relay mfr only guarantees 40dB, you have seen 60 dB? I
wouldn't be surprised, since the mfr is specing a "worst case under all
conditions and all manufacturing variation" kind of number.  Array Solutions
quotes 60-65 dB kinds of numbers for their AS1GRS232, and 55-60dB for the
SixPak (typical, not guaranteed), but doesn't quote any specs for the
RatPak, etc.

But even with 60dB, you're still putting 0dBm into the second receiver. If
you're expecting same band operation, that's a pretty challenging dynamic
range requirement if you're looking for narrow band signals at  -150 dBm
close to the noise floor.



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