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Re: [Antennaware] RF relay switching problem

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Subject: Re: [Antennaware] RF relay switching problem
From: "Paris Andreou" <>
Date: Mon, 29 Dec 2008 15:36:54 +0200
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Dear Bob, Guy and Martin,

Thank you all for your help and advice. Your input is highly appreciated. I
will get back to work with the ATU implementing your suggestions.

Best regards and a happy new year.

Paris 5B4XF

-----Original Message-----
[] On Behalf Of Paris Andreou
Sent: Friday, December 26, 2008 3:44 PM
Subject: [Antennaware] RF relay switching problem

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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