[Amps] rfi

[Keith Dutson]

RADAR is a completely different kettle of fish from stray RF.  With
sufficient power and directivity (e.g. military aircraft) it can literally
cook a person like being in a microwave oven.  I have first hand experience
from being about 100 feet in front of an aircraft when the RADAR was
(accidentally?) turned on.  This happened during a cold winter night on the
flight line while wearing a very heavy goose down coat.  The parabolic
antenna was fed with 12KW via waveguide and the occasion was electrical
alignment of the antenna drive system while observing power received on a
test set.  The RADAR would be turned on while standing about 10 feet to the
side, then turned off to check the test set and adjust the drive system.
The process usually took about 30 minutes.  But this time the guy in the
cockpit turned it on while I was setting up the test set.  Within a few
seconds I was warm as toast and, realizing what had happened, yelled back to
the cockpit to turn it off.  He did.  Good thing too, because I was about to
run to the cockpit and haul him out.

73, Keith NM5G


-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Max Harelik
Sent: Tuesday, May 01, 2007 11:41 PM
To: amps at contesting.com
Subject: Re: [Amps] rfi

This borders on OT, but I can't resist:

Back in my military days (1966-1970) I was an airborne weapons control
systems tech. Late one night, while completing routine maintenance on the
system and its radar, a green no-stripe came walking through the hangar with
an armload of 4 ft. fluorescent lamps. (You can already see where this is
going, can't you?).

(Normally, we had to work with the radar under an RF blanket to keep from
interfering with nearby commercial airport traffic. This night, however, the
airplane happened to be in a hangar whose doors were pointed out to sea and
well clear of civilian patterns, so I had left the blanket off the radome,
to see what I could see "out there". )

I recalled that one can check SWR on a mobile antenna by holding up a
fluorescent lamp next to it. I thought, "Well, he's not next to it, but I'll
give it a try, anyway," and with the aircraft hand control, made a sweep
past him. The effect was satisfying: The lamps lit up in a random fashion
(ghostly, if you will) and the troop froze, and with nothing moving except
his very wide-open eyes, looked fearfully around.

Now I was on the other side of the hangar, and he couldn't see me, hunkered
down in the cockpit as I was. After a bit, he tentatively took a step, and I
gleefully gave him another sweep. The lamps lit up again, he hollered, threw
them up in the air, and was out the door before they hit the hangar floor.

Figuring that I better vacate before he came back with his supervisor, I
finished up, buttoned up, cleared the A/C records, turned ground power off,
grabbed my tools, and headed for my shop at the far end of the hangar. Sure
enough, about 10 minutes later he was back with his Sgt, trying to explain
what had happened. I watched from my point of relative safety, as, with
frantic gesticulation and articulation, he attempted to convince his boss
that he hadn't just tripped and dropped the lamps. No go. He was made to
clean it all up, and they left the hangar. Probably had to pull some KP,
too, but I never knew for sure.

Disclaimer: We were instructed never to stand in front of the aircraft with
the radar system on, or point the radar continuously at anyone, (the
sustained RF could blind one, or worse, truncate one's reproductive
potential) but momentary exposure was deemed acceptable. So, I felt ok with
those quick sweeps. The cautions/orders were taken seriously, though we
occasionally target-practiced on birds out on the ramps with dramatic
results.

73,
Max, K5OVW
[snip]