Topband: Required switch attenuation...

[Michael Tope]

----- Original Message ----- 
From: "Dan Zimmerman N3OX" <n3ox at n3ox.net>
To: <topband at contesting.com>
Sent: Tuesday, September 11, 2007 8:49 AM
Subject: Topband: Required switch attenuation...


>I just wanted to check this with those with practical experience.
> 
> If you have a few flags in a few directions and want to build a
> switch, how much attenuation between ports do you need?
> 
> I'm thinking as little as 30dB would put even strong signals picked up
> by an opposite direction flag down in the noise of the desired
> antenna... but in practice, might I need more?
> 
> Building a switch is easy but building a high isolation one is maybe a
> little more difficult, and I should probably go into it with an idea
> of how much isolation I need.
> 
> (By the way, I know I could just build a rotatable flag, and used one
> last year, but I can use bigger ones more conveniently if I go with
> fixed-direction antennas)
> 
> 73,
> Dan


I  don't think you'll have too much trouble getting 40 or 50 dB 
attenuation at 2 MHz, Dan. Small DIP relays for instance should
give isolation on order of at least 70 to 80 dB at 2 MHz (probably
more). In fact, I  think you'd have to work hard to find a switch that
gives only 30dB isolation at 2 MHz. Its capacitance that kills of 
course, but since the frequency your dealing with and the 
impedance are both low, its hard to screw up. 

73 Mike, W4EF.......................