[MRCA] Gilbert Field Antenna Caution and Warning

[WA5CAB--- via MRCA]

Anything new enough to have to worry about co-location problems is also new 
enough to bring the owner/operator to the attention of the modern day 
Gestapo.  And too new to be discussing here.  Avoid it and you won't have either 
problem.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 09/23/2014 17:13:23 PM Central Daylight Time, 
w2hx at w2hx.com writes: 
> 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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