[RFI] Frequency-Specific Interference
kd7jyk at earthlink.net
Tue Feb 28 11:29:04 PST 2012
Back in 2004 I ran a beacon, RPG, on 13,555.430 KHz. It genrated a bit of
broadband hash from the Epson oscillator so I would shut it down when I
wanted to monitor HF.
Sometime around December of 2004, there had been some driving sleet and I
began to heard a strong pulsating broadband hash similar to to what my
beacon oscialltor would created, however it was one second on, one second
off. It was from a few tens of KHz to at least 30 MHz, the upper limit of
the receiver I had at the time.
I have a rotatable 10m dipole and tried to get a bearing on it, but it was
very strong with a faint null to the South. This made sense to me at the
time because with the dipole facing South, my beacon was off the tip.
I hiked out and shut off my beacon. Upon return to the shack, the noise was
still present. I thought that perhaps the odd-ball power supply I used had
capacitors in it I didn't know about and due to the low current draw, my
beacon was still operating.
I went back out and disconnected the transmitter and just in case, shorted
the input leads due to its own capacitors.
Still a broadband sound. I went back out to the beacon, this time with a
portable HF receiver. As I got closer, the sound increased! Now I'm really
getting confused! I ran my little receiver with it's ferrite bar antenna up
and down the beacon antenna and mast, yep, noise everywhere near the beacon,
still a null to the South, very strange.
The sound last for about three hours, then stopped and hasn't been heard
It was a couple of years later when passing through a portion of the Nevada
Test site and looking at some rather unobtrusive large metal sheds that I
recalled a story form a fellow I had spoken with one evening several years
earlier. His comment was something like this:
"You know those large metal sheds, they have simulators in them that can
create the conditions of outer space. We can put a device under a vacuum
and blast it with most any type of radiation, thermal, electromagnetic, even
nuclear. Right now we have a spy satellite in the chamber and we're
blasting it with RF, CW, from a few Hz to GHz with pulses up to three
MegaWatts. This will go on for days".
Fast forward a few more years, I run into another fellow from the NTS and
make a brief comment, "Did you have an instance a few years ago with one of
your chambers that may have generated external RFI?", "Yes, we had a loose
door for a few hours". I told him my general location and that I had been
blasted, resulting in my equipment being rendered near useless for that
period. He provided me with a phone number to call and told me "we REALLY
need to know when there is a problem detectable from outside, call this
number, when a person answers, tell them, "check your simulator doors""
More information about the RFI