[TowerTalk] remote ant switch decision

[Jim Brown]

On Tue,4/12/2016 7:17 AM, Tom_N2SR via TowerTalk wrote:
> That being said, I have a Top Ten unit and it works flawlessly.

An issue I found with the Top Ten 2x1 switch box is that it uses the 
chassis as the return. This causes SWR to rise with increasing 
frequency. I discovered that when investigating why SWR was rising on 
the circuits I was switching with it (including the input and output of 
my KPA500 with one pair of boxes and my SteppIR with another pair). I 
use both the SteppIR and the KPA500 all the way up to 6M. I didn't 
measure crosstalk, but I would expect it to also be degraded.

I've modified several of my 2x1 boxes by adding braid between each 
connector and the circuit board near the high side connection, and also 
between input and output sides of the board (because the "ground" layer 
is broken under the signal traces, another design error). [When there's 
a "ground" layer on a board, return current for a trace flows in a 
narrow area directly under the trace -- UNLESS the ground layer is 
broken, in which case it acts like an open shield on coax, and the 
return current takes whatever path it finds, in this case, the chassis.]

I'm using four of the Top Ten 6x1 boxes to switch stubs on 40M and 80 
dipoles. They work fine at those much lower frequencies, so I haven't 
bothered to measure their performance or open them up to check their 
construction. But I would expect to see the same design error, and I 
would not consider them for use at higher frequencies until I'd checked 
them out more carefully.

I used the same DG8SAQ VNWA vector network analyzer for the measurements 
that I used a couple of years ago for the survey of bandpass filters 
that ran in NCJ, and that is on my website.

73, Jim K9YC