[Elecraft] Looking for a way to switch an antenna input to the KAT500

[Jim Brown]

On 2/17/2019 6:26 PM, Randy Farmer wrote:
> I concur with the comments on the Top Ten 2-way switches. I'm using 
> about 10 of them at various places in my SO2R contest station antenna 
> and BPF switching networks. They work well and have good isolation. I

On the basis of my measurements with a Vector Network Analyzer, I am NOT 
impressed with these switches, and consider them poorly designed. The 
major design flaw is that they depend upon the chassis for signal 
return, so the signal path gets increasingly badly mismatched at 15M and 
above. I didn't measure crosstalk, but this design error would certainly 
impact it. I reduced the mismatch by about half by adding braid from the 
coax connectors to the circuit board and following (as best I could) the 
signal path to provide a return. Why? Because the "ground" layer is 
broken under the top layer, so it can't act as a return either!

Someone cited 50 dB as "good isolation." When I replaced my WX0B 6x2, I 
measured isolation of about 55 dB. The replacement, a 4O3A 6x2, measured 
75 dB worst case. And other one I'm using now, the 4O3A Antenna Genius, 
measures better than 95 dB worst case.

If you look inside a well designed power amp, you'll see transmission 
line running from input and output for both TX and RX path. My Ten Tec 
Titans were built that way, and so is the KPA500. You'll also see 
mini-coax jumpers tying sections of the K3 together.

73, Jim K9YC