[Elecraft] adjacent antennas and potential radio damage

[Charlie T, K3ICH]

Connect a "grain-of-wheat" light bulb across the unused coax and gradually 
increase transmit power.

I know this is a rather un-scientific, crude test, but simply put, you're in 
big trouble when it glows!

I tried this with a 600 foot Beverage that is, at it's closest point,  50 
feet from any transmit antenna.  On some bands, I could run a kW but  on 
others bands,  the bulb was bright at 150 watts out  I now have a Collins 
"RF Overload Protector"  (622-0908-001) permanently in the Beverage feed !

Better to use a GOOD antenna switch with published maximum isolation, or 
unplug the unused antenna.

73, Charlie k3ICH


----- Original Message ----- 
From: "Julie Royster" <jsdroyster at nc.rr.com>
To: <elecraft at mailman.qth.net>
Sent: Wednesday, April 16, 2014 11:06 AM
Subject: [Elecraft] adjacent antennas and potential radio damage


> Thanks to those who wrote me privately as well as those who replied on 
> this
> list (KL7UW and  K4NH ) regarding the possibility of damage to one radio
> from another radio transmitting on a nearby antenna.  For the benefit of 
> all
> I am pasting below highlights of the useful information I received.
> MANY THANKS!  I learned a LOT from you kind folks.
> Julie KT4JR
>
>
> Dick at Elecraft said:
> "At 5 watts it's usually not a problem, at 450 watts, you want to have a 
> bit
> of room (maybe hundreds of feet) between antennas.  The radios have some
> protection from overdrive.  Carefully planned with antennas end to end or
> facing different direction with enough space it's possible to share a band
> with multiple K3s.  But if the antennas are coupling sufficiently, it can 
> be
> destructive to the front ends of the radios.  I can't offer any guidance
> better than you've receive thus far. Every multioperator contest or Field
> Day station has to deal with this problem, and there are solutions, but 
> they
> require some effort, either bandpass filters to keep energy from nearby
> transmitters on other bands, or antenna placement planning, or some
> combination."
>
> AB9CA/4 said:
> "There are certain orientations which might allow simultaneous operation 
> of
> the two stations. If one antenna is a vertical and it can be placed on a
> line perpendicular to the mid-point of the Vee you should be OK. This is
> when the base of the vertical lies on the vertical part of a 'T' 
> arrangement
> with the Vee forming the horizontal top of the 'T' (looking down from the
> air). Place them as far apart as possible. There is minimum interaction in
> this configuration. With chokes in place and proper dress of the feedlines
> you could get maybe 60 dB of isolation between them...
>
> (On Field Day) Our club has used two stations on the same band, usually 
> 20m,
> with success. One on CW the other on Phone.  We did it with two wires
> arranged as I mentioned earlier, in the 'T' configuration.
>
> Especially note that damage can occur even if one rig is turned off.
> The antenna is still connected internally with power off. To be certain of
> avoiding damage it is best to disconnect the antenna from any rig not in
> use. And when you connect them be certain of what band the other station 
> is
> on (and make sure you are not on it!)."
>
>
>
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