[MRCA] Gilbert Field Antenna Caution and Warning

[Ray Fantini]

Almost everything built for military or commercial service in the last thirty years has adequate protection for operation in high RF fields, considering much of the equipment is expected to operate in a radio crowded environment. Most of the cheap Ham or bottom end commercial stuff has issues with overload and images, just think back to the garbage that Wilson produced in handhelds back in the eighties.  All of the General Dynamics family of R-1051 and the RT-618 transceivers have relays installed in the front ends with fast acting RF sense circuts to protect the front end in the event of a transmitter too close. 
All that being said still some common sense is required, if for nothing else then it gets hard to copy SSB when your too close to the other station. At Gilbert the net control for Fridays net, a PRC-47 was just about a mile away from me at Beltsville State Park and when they came up it was plenty loud on my Sunair. Think it may have been testing the limits of its AGC action. The Harris 5020 a tough little radio and would assume that in the design criteria it's expected that they will operate in close proximity at times but don't think I would try it myself with what the radio cost.
I also have to say that with the three or so PRC-47 transceivers in operation in the net I was impressed with the ability of net control to be heard by everyone and hear everyone with no issues using just the antenna mounted on the radio and a four wire counter pose. Good showing for those old radios.
So it was a good show for operation of Vietnam to newer family of SSB radios and an opportunity to set up and operate in the field in a real world example of their use. We also had much 144.25 URC-4 activity, maybe the largest collection of working URC-4 transceivers in one place at one time for the last twenty years? Dayton has the title of the largest collection of working BC-611 3885 AM transceivers at one location all in working condition for the WW2 net but think MRCA at Gilbert is now maybe largest field exercise for 60 meter SSB and primitive AM on 144.25 although will admit that I used a URC-110 for 2 meter AM. Dayton at least in my experience still keeps the record for most active backpack and handheld stations for its Cold War Net on 51.0, always around twenty to thirty people and the WW2 net on 3885.
Would wonder what the people out on the left coast are doing on there get together and if they are running field exercises too?


Ray F/KA3EKH

-----Original Message-----
From: MRCA [mailto:mrca-bounces at mailman.qth.net] On Behalf Of Peter Gottlieb
Sent: Tuesday, September 23, 2014 10:59 PM
To: mrca at mailman.qth.net
Subject: Re: [MRCA] Gilbert Field Antenna Caution and Warning

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
>>