[MRCA] Gilbert Field Antenna Caution and Warning

[Peter Gottlieb]

I would hope (!) those newer radios, which cost an astronomical amount, would 
have effective protection.

My old Harris RF-590A has a relay in the front end which isolates the receiver 
from the antenna at a certain level on the antenna (I've reached that a number 
of times when I had multiple antennas up and there was enough coupling).

Would they have reduced the protection for newer radios?




On 9/23/2014 10:46 PM, WA5CAB--- via MRCA wrote:
> 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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