adjacent antennas and potential radio damage

[jsdroyster]

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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[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" <[hidden email]>
To: <[hidden email]>
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!)."
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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[Mike Harris-9]

Quite so.

Forty years ago the FT101 had a front end protection circuit that
included a light bulb.  When I was in the Antarctic, location doesn't
really matter, my antennas were reasonably close and when I keyed the
main TX at 1500W the rear of the '101 would flash with the keying.
Never suffered a front end failure.

I have a circuit diagram dated 2010 for an "RX Protector", which
unfortunately doesn't offer any authorship detail, it looks similar to
the '101 circuit.  If anyone wants a copy let me know.

If the idea of a bulb and a couple of back to back diodes and big
signals worries you then perhaps making this as a piece of test
equipment to be used as a level reality check and then taken out of the
signal path is possibly the answer.

Regards,

Mike VP8NO

On 16/04/2014 12:40, Charlie T, K3ICH wrote:
> Connect a "grain-of-wheat" light bulb across the unused coax and
> gradually increase transmit power.
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[alsopb]

Guys,
There is no substitute for a measurement.  There is no global answer to
how close is too close or how much power is too much power.

Measurement process is simple:
1) Run one rig at 1 to 5 watts
2) Look at the S-meter on the other.
3) Scale the results upward by adding the number of dB to full power.
If this results in something > 80db over S9 then be concerned.  Consider
RX protection.

Do the same with the other rig transmitting.
You might consider doing this on all bands.

73 de Brian/K3KO


On 4/16/2014 17:08, Mike Harris wrote:

> Quite so.
>
> Forty years ago the FT101 had a front end protection circuit that
> included a light bulb.  When I was in the Antarctic, location doesn't
> really matter, my antennas were reasonably close and when I keyed the
> main TX at 1500W the rear of the '101 would flash with the keying. Never
> suffered a front end failure.
>
> I have a circuit diagram dated 2010 for an "RX Protector", which
> unfortunately doesn't offer any authorship detail, it looks similar to
> the '101 circuit.  If anyone wants a copy let me know.
>
> If the idea of a bulb and a couple of back to back diodes and big
> signals worries you then perhaps making this as a piece of test
> equipment to be used as a level reality check and then taken out of the
> signal path is possibly the answer.
>
> Regards,
>
> Mike VP8NO
>
> On 16/04/2014 12:40, Charlie T, K3ICH wrote:
>> Connect a "grain-of-wheat" light bulb across the unused coax and
>> gradually increase transmit power.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
>
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[KV5J]

"If this results in something > 80db over S9 then be concerned.  Consider
RX protection."

Elecraft should be able give us a figure on the RF protection that the K3 and KX3 have built in.
I'm sure it would be in the design.  Wayne? Eric?

Keith, XE3/K5ENS