[TowerTalk] More questions - wired wireless antenna switch

[Jim Lux]

On 1/16/12 2:54 PM, Pete Smith N4ZR wrote:
> This is further on the subject of the 315 MHz 8-position
> remotely-controlled switch that I'm trying to adapt to switch my RX
> antennas.  I have the two "couplers" rigged to couple the VHF to the
> feedline and pick it off at the other end.  However in examining the
> relay unit I see that the antenna for the receiver is a 13-turn coil of
> ~#24 hookup wire wound roughly to 3/8" ID.  It seems to me that such a
> coil might have a fairly high reactance at 300 MHz, and yet when I use
> the unit in open air, the relay unit switches reliably out to about 200
> feet, so it can't be too bad as an antenna.  My simple-minded question
> -- should I uncoil the antenna and see if it can reach the whole 300
> feet without coupling to the coax?  If I'm using the "wired-wireless"
> method, should I uncoil it before connecting the free end to the
> coupling loop?  The loop, per earlier advice, is about a 1" length of
> hookup wire laid next to the center conductor of the coax (shield removed).
>


You might want to be careful.. that coil might be part of a low Q tuned 
circuit to provide selectivity for the front end.  This was pretty 
common on those FM band wireless mics back in the 70s.. the tank was the 
radiator.