For the heck of it.

[merlin]

I dusted off an old radio stuffed with marine channels and getting a couple digital signals where not expected.
Too far from Seattle to be originating there or the skip is topped out.
Rarely I get a bit of chatter from the lake but advisories and time, no one on the lake.
The frequencies are 156.2535 and 156.680 intermittent. Just curious what it may be. Not exactly marine channels.
Not AIS or the likes.

 

[mmckenna]

Some of the marine channels are reused for LMR when far enough inland.

 

[ecps92]

156.6800 is not VHF Marine and is not even a VALID FCC channel allocation [156.6750 is]

FCC VHF High Band - Scan New England Wiki

www.snewiki.com

nor is 156.2535 a Valid allocation

I dusted off an old radio stuffed with marine channels and getting a couple digital signals where not expected.
Too far from Seattle to be originating there or the skip is topped out.
Rarely I get a bit of chatter from the lake but advisories and time, no one on the lake.
The frequencies are 156.2535 and 156.680 intermittent. Just curious what it may be. Not exactly marine channels.
Not AIS or the likes.

 

[merlin]

Some of the marine channels are reused for LMR when far enough inland.

That is what it looks like, but these odd freqs are not standard and can't find FCC listings.
Almost thinking some bootlegging going on.

 

[merlin]

156.6800 is not VHF Marine and is not even a VALID FCC channel allocation [156.6750 is]

FCC VHF High Band - Scan New England Wiki

www.snewiki.com

nor is 156.2535 a Valid allocation

That is why I questioned this. the frequency's I posted are +- 20 Hz according to my equipment.
In scan mode, they are close enough to break squelch in standard marine channels.

 

[ecps92]

or your equipment is off freq

That is what it looks like, but these odd freqs are not standard and can't find FCC listings.
Almost thinking some bootlegging going on.

 

[mmckenna]

That is what it looks like, but these odd freqs are not standard and can't find FCC listings.
Almost thinking some bootlegging going on.

Yeah, I think I'd calibrate everything/figure out what the offset is and go from there. I think that might be part of the problem.

As I said, some of the marine VHF frequencies are reused. Some of it is 'free banding', baofengs, crappy equipment, and others doing 'stupid radio user tricks".

 

[AM909]

@merlin: Or you're hearing an image or intermod. What equipment? What's the first IF frequency?

[time passes...] Now I that I look at the screen pic, it is from SDRsharper – is it an SDR? Also, the freq shows 156.688657, which is close enough to 156.6875 (a real interstitial marine channel; +1160 Hz away) for that to be real, though I don't remember the status of those interstitial channels.

 

[merlin]

or your equipment is off freq

The equipment is <20 Hz off frequency. Trust me, these are not licensed frequencies by the FCC.
They are strong enough to be local and across the band, there is one legitimate LMR channel in use.

 

[merlin]

@merlin: Or you're hearing an image or intermod. What equipment? What's the first IF frequency?

[time passes...] Now I that I look at the screen pic, it is from SDRsharper – is it an SDR? Also, the freq shows 156.688657, which is close enough to 156.6875 (a real interstitial marine channel; +1160 Hz away) for that to be real, though I don't remember the status of those interstitial channels.

I could post a photo of the radio with the busy light blinking. I fired up SDR#r to further analyze the signals.
Plugged into DSD+ there is no decode. I'll put this in multi-PSK later and see if that tells me anything.
No, 156.68865x is accurate. Not an image or harmonic. This overlaps into the guard band area at channel 73.
Close enough to open the squelch on the radio and stop the scan.
The radio is an M7100 MaCom I loaded with marine channels for scanning.

 

[Ubbe]

When carriers are not following normal channel steps then suspect interference from electronic devices like computer, tv boxes, routers and such. I have plenty of those digital modulated carriers that all origins from my own electronics.

/Ubbe

 

[merlin]

When carriers are not following normal channel steps then suspect interference from electronic devices like computer, tv boxes, routers and such. I have plenty of those digital modulated carriers that all origins from my own electronics.

/Ubbe

Well, 40+ years of advanced communication, RF engineering, I doubt any body here could call this closer than I have.
NO WAY is it some by product of image or intermod, these are first order carriers and the very reason I questioned this at all. Its origin is other than within the building so not computer related, not cable related, not satellite related.
My closest suspect is medical equipment at the hospital a mile away. Tonight, the signal at 156.68 is gone, the other is there and an S4 using my SDR. There IS some digital modulation but nothing I have decodes or identifies it.

 

[Ubbe]

Could you make a sound sample available or even a IF sample? It would be interesting to listen to if it can be recognized. The modulation of the frequency in the last screenshot doesn't seem to look the same in the + and - modulation, it's uneven which makes it a bit strange. Maybe it's a SSB signal, there's a small signal to the right of it that could be the remains of a main carrier, or else it doesn't look like anything that are supposed to intentionally carry any reliable info using a RF signal.

/Ubbe

 

[merlin]

OK, I will try to work up a sound recording. Your statement " doesn't seem to look the same in the + and - modulation, it's uneven which makes it a bit strange." I noticed. and strange it is.
I will take a closer look at SSB, but this is a "strange" SSB signal at best.
Sigidwiki has nothing like it.
Thanks.

 

[merlin]

I expanded the waterfall to 48 Khz, the better to see the discrete phases.
Also a 20 second WAV file.
The file is to big to upload here so no luck with that part.

 

[Ubbe]

The file is to big to upload here so no luck with that part.

RR doesn't allow much to be uploaded. Even when you post a lot of screen shots will it soon reach its upload limit. Use OneDrive, Google drive, or similar external storage place and link to it.

/Ubbe

 

[merlin]

This will be a while, I can't get files to synch on one drive or icloud.
I am going to start an account on mega and go with that.

 

[Ubbe]

Create a drive.google.com account and you do not need to sync, just upload files and right click on them to share.

/Ubbe