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[Antennaware] RF relay switching problem

To: <>
Subject: [Antennaware] RF relay switching problem
From: "Paris Andreou" <>
Date: Fri, 26 Dec 2008 15:43:43 +0200
List-post: <">>
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

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