Thursday, July 15, 2010

I want to use one coax run for my VHF and UHF station, but I ...

Q Kaehu, WH6WW, asks, “I want to use one coax run for my VHF and UHF station, but I also want to have a vertical and a beam. I think a coax relay would provide the solution. Is this something I could fabricate from RadioShack components or should I buy one commercially?”

A When switching multiple feed lines, the impedance of the switching network is a prime consideration. The impedance of a feed line is a function of the conductor surface areas and the spacing between them. When you insert a standard type of relay in the line, you will have a point with a different impedance, with a resultant change in SWR. At HF, the SWR difference is not likely to be significant, but at VHF and UHF this is not the case. This doesn’t make homebrewing impossible, but it does add a major complicating factor.

Remote coax relays are available for VHF and UHF, but they are costly (it may be cheaper to run multiple lengths of coax). If the cost is not a consideration, you can purchase a remote coax relay from these folks:

Electronic Switch Co
8491 Hospital Drive
Suite 328
Douglasville, GA 30134
tel: 770-920-1024

from QST May 2000