[Antennaware] RF relay switching problem

[Paris Andreou]

Hello all.

 

I am not sure if this question applies to the list, but if any of the gurus
out there can help, it would be much appreciated.

 

I have built a remote ATU to use at the base of a 66-foot vertical. The
antenna is resonant on 80m and I have built 2 L-networks to feed the antenna
on 40m and 160m (one for each band). The networks consist of overrated
roller inductors and air-spaced capacitors. Networks work fine at high power
when used on their own or switched using big rotary switches. 

 

I bought big relays rated at 10KW to switch the networks. The relay control
cables and coax go from the shack to the base of the antenna about 1 metre
below ground. The problem is that at high power there is arcing and relay
coil overheating. I cannot tell exactly where the arcing occurs, but it
appears that RF is coupling into the relay frame/coil or arching between the
contacts and the coil.

 

I have added a diode and 0.01 uF capacitor across the relay coil, but this
has not solved the problem.

 

Has anyone come across a similar problem? Is my suppression circuit
inadequate? Does the position of the ATU box matter (eg bury below ground)?

 

 

Thanking you in advance,

 

Paris 5B4XF