Going on a road trip this weekend across the West Coast, Curious to see what is the best thing or the most enjoyable thing you guys have tracked? I’m thinking about running the kraken for a while while i’m traveling and seeing what I can track, I think it would be really cool!
I Have tracked a lot of things in my former job…a submarine stuck with carrier on CH16, an EPIRB transmitting, (found in a post office). Fishing boats using flight radio for communication between the ships, and disturbed flight traffic. Heart monitor in a hospital that had a fault and transmitted on a TAXI repeater input. A reporter on a local radio station using a link on wrong FQ…etc etc etc…and a lot of mobile telephones repeaters that private people installed…that interfered on mobile network. And a lot of more…sometimes angry people…that didnt understand that they used illegal transmitters.
And sometimes we did raids on 27.555 MHz, found sometimes HAMs using that FQ…sent warning letters…it was a fun work. Fox hunting every day. DFing is very fun and interesting.
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Oscillating mast mount TV amplifiers. Drifty as hell.
The case of the Horrible Noise:
Ham 2m repeater (600 khz TX/RX split) Occasional bursts of a HORRIBLE loud noise, hard to describe but you’d know it if you heard it. Only occurs during wet weather. There’s a bit of an “echo” quality to it.
I was never able to get to the root of the problem, but I suspect it was a switching power supply located somewhere near the transmit antenna. (top couple floors of the building) When the repeater was installed in the 70’s that building was a quiet place. Fast forward 30 years and computers and power supplies are everywhere. Switching power supplies especially can have energy in and around 600kHz. I suspect the transmit signal from the repeater was illuminating some SMPS somewhere, which then mixed the transmit signal up and down 600kHz, and this was then radiated, showing up on the input of the repeater, and round and round you go. The echo quality in the sound was the big clue, as the repeater had a small audio delay built in so that we could strip off DTMF command codes without them appearing on the output.
Unfortunately this would only occur every few months, and never when you expect it.
You can’t DF 'em if they don’t transmit!
Solved by Eyeball MK1:
The boss sends me out to one of the phone systems we maintain. The complaint is a periodic “beep” that comes and goes. Lots of other techs have been out and swapped out everything you could think of, but no solution.
I get there, pick up an extension, dial a digit to stop the dial tone, and there it is. Beep… Beep… Beep… Very regular. I think about what might cause that sort of noise. While I’m thinking I’m looking out the window… Thinking, Beep… Thinking, Beep… I’m looking out the window at the boats in the marina, and one of them has radar running, and every time the antenna is broadside to us, BEEP!.. BEEP!.. The semiconductors inside the extension are directly rectifying the GHz radar pulses.
A great case of “You can’t fix it if it ain’t broke”. A classic case of part 15 in action. I called the harbor master and he said that everyone is supposed to shut off their radar in port, but some just won’t do it.
Had a few fun ones.
- Local DPW reported strong interference on their primary voice channel. Found it was only for 20sec twice/day. Strength varied widely during the 20sec. Turned out to be 2-way outdoor siren system in the next county polling each siren status. Same frequency and PL tone. (Found with doppler and assisted by local ham monitors).
- Local ham reported new continuous interference on 2meter satellite (low power) downlink frequency. Tracked to nearby elementary school that installed new RF adjusted classroom clocks. The controller transmit frequency was exactly 1/2 of the sat channel. NanoVNA showed harmonic was bigger than the fundamental. The school system was very cooperative, found the same issue at another school nearby. Reported to the manufacturer, resolution unknown.
- Ham Club emergency operations 2 meter repeater kept experiencing random noise issues. Signal was extremely weak, popping up briefly now and then. Several trips around the local area couldn’t find it, so kept expanding the search radius but signal was too weak and intermittent to directly track. Was about to give up at 50mi when signal strength popped up again on freeway overpass. Turned out to be stuck repeater, 5khz off from ours, over 100mi away. Signal variations when tracking were due to terrain topography.
If you want some practice, start with local FM broadcast, National Weather Service or trunked public safety systems. Happy hunting.