VHF Marine Ch 12 Stuck Transmitter 12/12/20

[avascan522]

If anyone is looking for a fox-hunt challenge, or even better, has a doppler or other RDF equipment, there has been dead air on VHF marine channel 12 since about 4pm today (12/12). 156.600 MHz
With no attenuation, the signal is full scale in Avalon harbor, but with some attenuation, removing and replacing antennas, and a boat ride around the harbor, I came to the conclusion that it is not in Avalon or the harbor. Sounds like it could be a strong transmitter on the mainland - I can even receive it from up Avalon Canyon, away from the water, where a low-level transmitter would fizzle-out.

 

[mmckenna]

If you run 156.600 through the FCC database, there are a number of harbor districts, port districts and commercial users on that frequency. Many are running 50 watts from fixed stations on shore. With a good antenna, they could certainly be blasting Avalon pretty well.
Since some of those are wireline control from remote locations, it could be a faulty circuit, tone remote, etc.

 

[cmdrwill]

No TOT ????

 

[Floridarailfanning]

No TOT ????

If it's a shore station like @mmckenna suggested it's probably a base radio or repeater that's rated for 100% duty cycle.

 

[avascan522]

After deliberating with a ham operator in North Orange County, he told me he was able to receive the signal using upper sideband (USB). However, when he switched to FM, he was not able to receive the signal. For me, the signal is decently strong for me to receive at my house with antenna outside in FM mode. When I use the RTL-SDR software in CW mode, I hear a steady tone. USB- nothing. FM- nothing. I heard the tone disappear once in about an hour and-a-half of listening.
Link to a video I recorded below:

 

[prcguy]

Is this still going on? I have nothing at my location, which is not bad for LA to San Diego coastal reception.

 

[avascan522]

Is this still going on? I have nothing at my location, which is not bad for LA to San Diego coastal reception.

Yup. Still the signal on FM, still the tone with CW mode. Hasn't stopped since. Thought about phoning the coast guard, but chances are they won't care since it's not on 16 or 22A. Would be as easy as using an RDF and taking a drive along the waterside of Palos Verdes to get a multi-point fix.

 

[prcguy]

I forgot I have a marine shore station with Sinclair 4-bay dipole in a 9dB pattern that covers roughly Avalon to Mexico. Still nothing with that. Maybe its blocked by PV and in the Redondo beach area or north? Or if you are receiving really strong at Avalon I suspect its somewhere around the island.

 

[avascan522]

Aside from the one station I spoke with in Orange County who thought he heard something, no one else seems to be able to receive this signal.

Know why? After an evening of running around with three devices (a ham HT on normal receive, a radioshack scanner with the antenna on and attenuator on, and a Uniden scanner with the antenna off and attenuator off), I can theorize that the offending signal is coming from...

Christmas lights on main street/front street right by the water. Don't ask me how. Once morning rolls around and the lights shut off, I'll know for sure.

I went around a hill up the coast, signal got very weak, even on the HT. Went down the coast from downtown, around a hill, same thing. Up the canyon and into a side valley? Again, lost line-of-sight. Weird.

 

[xilix]

[...]
Once morning rolls around and the lights shut off, I'll know for sure.

So was it the Christmas lights ?

 

[ecps92]

A friendly call to the USCG would still be in order, they can atleast use Rescue 21 to DF the signal closer to the source

If anyone is looking for a fox-hunt challenge, or even better, has a doppler or other RDF equipment, there has been dead air on VHF marine channel 12 since about 4pm today (12/12). 156.600 MHz
With no attenuation, the signal is full scale in Avalon harbor, but with some attenuation, removing and replacing antennas, and a boat ride around the harbor, I came to the conclusion that it is not in Avalon or the harbor. Sounds like it could be a strong transmitter on the mainland - I can even receive it from up Avalon Canyon, away from the water, where a low-level transmitter would fizzle-out.

 

[prcguy]

If lighting is making noise its usually broad band from a switching power supply and not at a stable specific frequency. If you can receive it in USB mode where you have a beat note and that note is stable over time then its a very stable clock behind whatever the source is and not a switching power supply.

The USCG might give it a look but I would not call them on the radio or use any emergency number. Hopefully there is a general purpose phone number for LA Sector at Terminal Island. I believe the USCG stuff on Catalina is at Black Jack mountain and that might be shielded some from Avalon for weak signals.

Aside from the one station I spoke with in Orange County who thought he heard something, no one else seems to be able to receive this signal.

Know why? After an evening of running around with three devices (a ham HT on normal receive, a radioshack scanner with the antenna on and attenuator on, and a Uniden scanner with the antenna off and attenuator off), I can theorize that the offending signal is coming from...

Christmas lights on main street/front street right by the water. Don't ask me how. Once morning rolls around and the lights shut off, I'll know for sure.

I went around a hill up the coast, signal got very weak, even on the HT. Went down the coast from downtown, around a hill, same thing. Up the canyon and into a side valley? Again, lost line-of-sight. Weird.

 

[avascan522]

Sometime Sunday during the day, the offending signal resolved itself. I never noticed a degradation in signal strength and was still attempting to track it down that morning until it stopped.
Could have been a faulty radio, and possibly the battery supply died. Still confuses me how it would generate that type of noise when decoded on SDR in CW mode.
Think I'll be investing in some DF-ing equipment in the near future in preparation of any incidents like this that come up later.

 

[prcguy]

You mentioned it was full scale on your SDR. As a sanity check you could take a 2m hand held at 1 watt for reference and see how far you can go and still get a similar reading on the SDR. That will give you an idea if it was a very low power device close by or if it had to be a radio with some power to get that level.

 

[avascan522]

You mentioned it was full scale on your SDR. As a sanity check you could take a 2m hand held at 1 watt for reference and see how far you can go and still get a similar reading on the SDR. That will give you an idea if it was a very low power device close by or if it had to be a radio with some power to get that level.

It still stumps me. I went through the harbor in a skiff with a handheld and a scanner, antenna on, antenna off, attenuator on, attenuator off... as good as I could get without a directional antenna and never got a strong enough signal to believe that the transmitter was on a boat in the harbor. Without better equipment, it was a fool's errand.

 

[vagrant]

Direction finding with a handheld receiver is very much possible:

1. Hold the receiver/scanner mostly upright, close to your body and look at the signal meter, or listen to the signal. A functioning meter is best though. Slowly turn in a circle and see where the signal is strong and weak. This is called body fade, as your body acts as a shield. Move a reasonable distance and keep doing that spin to get an idea of the direction of the signal, then keep moving toward the signal and keep doing the spin move.

2. Once the signal gets too strong, no difference on meter, turn on attenuation. If the attenuation is too much, simply dial it slightly off frequency instead and spin again.

3. When you get close, turn on attenuation and dial slightly off frequency as well. Turning your back to the signal to block the radio instead of facing it at that point will give you an idea of the direction, or you may be nearby if the signal is quite strong.

3. b. Once you feel you are quite close to the signal, dial your receiver to the third harmonic frequency which is 469.8 MHz. This attenuation really helps with strong nearby signals along with the body fade movement. You may or may not need to enable the additional built in attenuation at that point.

Initially, your movement may require a vehicle/skiff. As you get closer, stronger signal, you may be on foot. This method of direction finding has been around for years and I have used it myself successfully during amateur radio fox hunts where driving for miles was involved at times. If you want to experiment/practice while that signal is offline, dial up a nearby transmitter that is always on. Perhaps a local airport ATIS, but not a broadcast FM station as that signal is too strong. Having a signal constantly transmitting makes it much easier to find. With amateur radio fox hunts, the signal is mostly off in order to simulate a situation where a person is performing limited transmitting with a handheld radio in order to save power.

One improves with practice.