Topband: Relay switching at the base on antenna

[Augie "Gus" Hansen]

On 9/23/2017 6:39 AM, MR TREVOR DUNNE wrote:
> Can Anyone tell me a simple way to switch a 12v relay at the base of an antenna using the rigs ptt as the trigger??

If you're using a coaxial feed line, you could use a pair of "bias tee" 
devices, one on each end of the coax, to put 12 VDC on the line during 
transmit and 0 VDC during receive. Here is some info on bias tees. They 
are available commercially and can be home-brewed using readily 
available components.

     https://www.everythingrf.com/community/what-is-a-bias-tee

If your rig has a key out connector it is likely providing a contact 
closure to ground during TX and open circuit during RX. Use that to 
switch 12 volts from the rig or a separate supply on during TX using an 
auxiliary relay or solid state switch, and feed that to the bias tee. 
Pick off that DC control voltage to activate the relay at the antenna end.

NOTES: 1) The series capacitors go toward the transceiver and antenna 
respectively to pass RF while blocking the DC. The RFCs block RF but 
pass the DC control signal. 2) If you are going to use both positive and 
negative voltages as control signals for more complex switching over the 
coax be sure to use an isolated, separate power supply.

Gus Hansen
KB0YH