[MRCA] Gilbert Field Antenna Caution and Warning

[W2HX]

Hi Breck, et. al. That was me! My Harris RF-5020 gives S meter readings and it read S9+90.  You are, of course, correct about close co-location of transmitters. My hunch is, after a certain generation of radios, the "newer" ones had very good protection in the front ends. After all, in a combat environment, you can't exactly tell the other guy to move further away, hihi. In my Harris, it has very stout PIN diodes to protect the front end. I can do some math, but based on 65V worth of pin diode protection, that is something like 80W directly injected into the receiver.  I wouldn't try it, however. But your point is well taken. Some of the radios we use are likely not to have such good protection (or any for that matter)!

73 Eugene W2HX


-----Original Message-----
From: MRCA [mailto:mrca-bounces at mailman.qth.net] On Behalf Of B. Smith
Sent: Tuesday, September 23, 2014 1:41 PM
To: mrca at mailman.qth.net
Subject: [MRCA] Gilbert Field Antenna Caution and Warning

When I checked into the HF field exercise last Friday I heard one station mention that the nearby station was "90 db" over S9 or something similar.  How he measured that I have no idea.  :-) I caution those that set up in the field particularly in groups to be aware of the strong RF fields present from near by sets.  ( no this is not a lecture on RF safety) but a warning that is  easy to burn out or blow the front end of those expensive modern radios. Its very hard to replace the front end device (FET's etc) on the older radios with discrete components but it is a nightmare on the newer radios, some of which have sealed modules.

When the other nearby station transmits disconnect your antenna or 
ground it, turning the set off may not be a solution.   Be especially 
careful when setting up your portable antenna near a fixed wire antenna. 
Good rule of thumb if the other operator is within hailing distance (you can hear them with out a radio) then that is close and precautions should be taken.

The same precautions should be taken when mounting antennas on a military vehicle, on some mobile installations I have measure a several tenths  of a watt in dissimilar antennas that were close to each other with power levels in the typical mobile range. On my military vehicle I would lower the antennas that were not in use so that they were not vertical and parallel  with the active antenna.

Z
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