[TowerTalk] isolation and SWR

[Jim Lux]

On 9/10/12 8:03 AM, Pete Smith N4ZR wrote:
> Just now, I was fiddling with my homebrew 80m array switchbox.  I have
> only two dipoles on it at the moment, both reasonably well matched.
> Accidentally I switched to one of the unterminated positions, and got an
> SWR on the order of 4.5:1 (feeding the dipole switchbox through my
> Ameritron RCS-10.  By comparison, if I disconnect the feedline inside
> the shack, the SWR is in excess of 25:1, and if I switch the RCS-10 to
> an unused position, I get 4.5:1.
>

So, the RCS10 has mostly good matches on most of the outputs, and one 
that's unterminated.  When you switch to the unterminated one, you get 
4.5:1, and 1:1 if you switch to the others?  And this is at 3-4 MHz?

4.5:1 is a return loss of about 4 dB.  That is.. if you had a 2 dB pad 
in line and a dead short, that's what you'd see.    How long is the coax 
to the RCS-10?   Is 2 dB of loss plausible?





> Is there even an approximate relationship between these various SWR
> numbers and the degree of isolation afforded by the two switchboxes? And
> probably an even dumber question.  If you have two devices in line and
> each has (say) 30 dB isolation between a line in use and an unused one,
> both of which pass through them both, is the resulting isolation 27 Db?
> Some other number?

Are you talking two switches in series?

>
> Be gentle - I was a liberal arts major.
>