[Elecraft] Was Amplifier - Now RF exposure limits

[Wes Stewart]

I spent a good part of my career at Hughes Aircraft working on the Phoenix 
Missile transmitter/receiver unit.  Being an RF guy I was asked once to design 
and build a 225 MHz PA that would deliver a couple of hundred watts output when 
driven by an HP608 signal generator. The object was to drive a 10 dB gain Yagi 
that would illuminate a Phoenix in a lab to simulate what the missile was seeing 
under the wing of an F-14 on the deck of the carrier Enterprise.

Phoenix had a feature called MOAT (missile-on-aircraft-test) that preformed some 
limited tests just before the aircraft was launched.  A lot of failures were 
happening that could not be repeated after the aircraft was removed from the 
flight deck and the missile unloaded.  Of course this was an operational PITA 
that needed fixing.  It was finally hypothesized that the failures were due to 
RFI from the AN/SPS-32 OTH radar that was a feature on Enterprise.  Some 
analytical type determined that 100W into the Yagi 10 feet from the missile 
would be the equivalent of what the missile and the deckhands were seeing on the 
carrier deck.

Since our lab didn't (yet) have an anechoic chamber large enough to do the test 
these guys planned to do it in a regular lab environment.  I told them that I 
would (and did) build the PA, but I didn't want to be anywhere near it during 
the testing.  I'm glad I wasn't on the carrier deck either.

Wes  N7WS


On 4/7/2017 5:05 PM, Fred Jensen wrote:
> On 4/7/2017 4:05 PM, Ron D'Eau Claire wrote:
>> Remember, the microwave oven was "invented" by an engineer working around
>> magnetron RF sources and discovered the "Hershey" chocolate bar in his shirt
>> pocket had melted. When he figured out why, the "Radar Range" (first brand
>> of microwave oven) was born.
> So the story goes.  However, I believe I invented the microwave oven when I 
> discovered I could cram a hot dog into the feedhorn and it would heat up in a 
> few tens of seconds.  Sadly, Amana came along with the name "Radar Range," and 
> "cram it into the feedhorn" as a name was consumer toast.  I've also noted 
> that chocolate bars get really soft in my shirt pocket, magnetrons or not.
>> One cold night in the late 1950's, working outside on a flight line of F-86D
>> fighters lined up wingtip to wingtip for preflight repairs and testing, I
>> concluded I must be catching the flu. I felt weak hot and sweaty after
>> several minutes talking with someone. We were standing in front of the
>> planes, most of which had the nose radomes removed for testing the
>> fire-control radar systems. Looking up, I noticed the radar antenna of one
>> plane across the way with someone sitting in the cockpit was pointing
>> directly at me. On a hunch, I took a few steps to one side and the antenna
>> twitched to follow me. I immediately moved completely out of the way and
>> within a short time I felt quite normal.
> Working my way thru college at the local TV station, the CE offered me $50 
> each time to climb the tower and replace the clearance lamps twice a year.  
> FAA requirement.  They sent me to climbing school at the local utility, 
> provided an approved harness, I "climbed" on a ladder inside the tower with a 
> fall arrestor hooked to a cable down the center.  $50 was big money then.  We 
> were on a ridge, I could see the Pacific after 100 ft or so, wind was 
> constant, and it was cold even in summer.  I climbed in the warmest part of 
> the day, and we were on the air of course. The last clearance lamps were at 
> the base of the mast holding the turnstile antenna, bottom of which was about 
> 40 ft above me.  I warmed nicely doing those three lamps, and it made the 
> downhill leg a lot more comfortable.  OSHA today would have had a cow.
>
> I use an HOA-Stealth antenna with my K3 at home, an end-fed wire along the 
> wooden fence.  I did the calcs, and at 100W, we're definitely safe.  I do 
> flash the two touch lamps in the bedroom on 80 and 160 but those things will 
> turn on if I sneeze. [:-)
>
> The calcs are really easy on the on-line devices, I used the ARRL one.  Paste 
> the results in your station notebook and you're home free.
>
> 73,
>
> Fred ("Skip") K6DGW
> Sparks NV USA
> Washoe County DM09dn