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Author Topic: What is the device?  (Read 78532 times)

Posts: 56

« on: February 22, 2012, 10:12:06 AM »

Have been plagued with a drifting up RFI signal into the lower six meter band, which has become a daily background nuisance while trying to hear any CW beacons. It's a wide band analog FM mode TV audio signal which drifts up from 49.935MHz into the lower part of six meters, and will peak around 50.020 to 50.045 or in some cases drifts as high as 50.060MHz. This happens twice during the day, with an occasional kid's cable movie drifting audio heard at mid day. The evening signal starts around 1800 local time and is the stronger than the morning signal and drifts into the ham band by 1900LT. The drifting signal will carry local digital OTA or what sounds like cable TV, or "on demand" TV programming audio. Repeated field surveys in mixed residential & commercial property with a rubber "ducky" handheld scanner can't pinpoint the exact location of this device, if any, and many times "pinpoints" to structures turns out wrong. Estimated area of coverage is over a one mile of the qth. During the field surveys, the drifting RFI signal was discovered to be enhanced when the scanner is held next to metal street light poles, and to a lesser degree next to other metal objects like fences or street signs!
Here's a summary of some additional clues:
-   A Six meter 3 element beam shows strongest strength toward the south of the qth.
-   A local OTA sunrise news show is heard starting abruptly at 0530 with a predictable 0700 audio cut off, then becomes dead carrier at the TV network switch over.
-   Only five of the nine local digital OTA station audio signals are even heard.
-   Long periods of dead carrier are heard prior to audio starts.
-   The dead carrier begins to fade away following abrupt audio cut off.
-   The longer the audio is on, the higher the signal will drift, until at some point the drift will stop and reach an upper frequency limit.
-   Abrupt audio starts and stops are heard during and at the end of some TV shows and movies and is followed by a dead carrier.
-   A Warner Brothers signoff tune and repeating music loops between and at the end of some programs are heard.
-   Syndicated TV shows heard are out of time and content sync with cable listings of the day; The Gilligan's Island theme song introduction was heard repeating a continual drifting audio for over 15 minutes, one night!  

de kb7wox
« Last Edit: February 23, 2012, 08:13:24 AM by KB7WOX » Logged

Posts: 7718

« Reply #1 on: February 22, 2012, 05:04:44 PM »

It is a TiVO unit with self oscillation. 


Posts: 56

« Reply #2 on: February 25, 2012, 04:37:10 PM »

Update: On 25 February 2012 starting at 2126z heard a music loop of what sounded like Xmas “lullabies” in muzak format on 49.980 and then drifting up to 50.025 by 2230z. After 2300z tunes gone just dead carrier weakening and dropping in frequency.  

TV audio started back up at 0203z 26 February, on 49.985 then lots of channel switching with final settling on local digital OTA PBS digital sub channel. By 0300z the signal had drifted up to 50.000MHz. At 0309z more channel surfing, signal now at 50.005, 0315z more channel switching, then to a sit-com show on “MynetworkTv”. As show continues hear an occasional audio streaming breakup sound, signal at 50.010MHz. At 0340z signal continues to drift up to 50.015, by 0425 at 50.020 (the evening max frequency), 0445z audio streaming break ups. At 0459z channel switching back to the PBS station. To remain thru 0800z when the program schedule repeats back to what was on at 0200z.
« Last Edit: February 25, 2012, 09:10:23 PM by KB7WOX » Logged

Posts: 7718

« Reply #3 on: February 26, 2012, 09:12:23 AM »

Are you DFing the source? It certainly sounds like a consumer item being used in someones home.

Posts: 56

« Reply #4 on: February 26, 2012, 12:26:00 PM »

As predicted the 50.020 was gone the next morning with some kid’s movie starting at 1632z moving the signal or harmonic up to 50.010 by 1832z and then the dead carrier fading away down to a weak 49.970 spot.
DFing based on the strongest metal street light poles, which so far shows a more north/south reach than the east/west coverage.  Using a hand held scanner with a rubber “ducky” tuned to the last drifted frequency, as I go out the door. I can pan the horizon for a direction toward a structure, find nothing on arrival by asking the owner what they are watching and discover the same signal strength back from where I came.
Discovered a parallel audio signal in the 49.705 to 49.715 frequency range doing the same thing; long period of a dead carrier, cable TV audio and movies, weird music loops, abrupt audio starts and stops, but has a different audio program at the same time as the “drifter signal”. This “signal” has a much more distorted compressed audio. Not sure if this one relates to “drifter” or is some other source?  This signal never shows up on the handheld during local searches, only using the 3 element beam.  

Both "signals" during dead carrier periods are heard on the beam with random weak "clicking" sounds.
Appearances of the signals in the evening and on weekends rather than during normal business hours, does suggest a device in someone’s home.
« Last Edit: February 26, 2012, 12:36:29 PM by KB7WOX » Logged

Posts: 17483

« Reply #5 on: February 26, 2012, 03:12:12 PM »

We had a case of this recently.  The cause was a pair of wireless headphones connected to a TV,
which is why you are hearing the TV audio, but the channel changes.  Apparently they were
being sold by a major chain store.  The oscillator doesn't stay on the design frequency (if it
even starts there in the first place).  The power might be higher than permitted as well.

Posts: 56

« Reply #6 on: February 26, 2012, 04:05:30 PM »

After roaming around the neighborhood for two hours this afternoon on a strong signal at 50.020, nothing, no device, no headphones, nothing found.  

After a repeating music loop some kid's movie has started at 0245z 27Feb2012 on 50.040, any hams driving by on Sunset Hwy (26) pull over and give it a listen.
Movie over at 0418z.
Hams on or near 26, listen for channel switching, music loops, foul language, sit coms out of sync with the clock, TV audio continue until 0655z tonite, dropping frequency to 50.030, with continual "gaming" type movie sound.
Nothing found this morning at 1215z, will be looking for morning start at 1330z on ~49.950 with local sunrise news show.

As predicted sunrise news show signal shut off comes at 1503z, total drift range 60khz.

At 1550z the parallel audio signal at 49.710 abruptly became active, but the TV audio is too distorted, sounds like a cable sports channel. At 1635z abrupt stop to distorted TV audio.

The TV audio has started at 2040z on 49.960 and has begun its drift upward. For any six meter ham traveling on Sunset Hwy near Bronson Creek listen for a western movie with lots of foul language. Sounds like the same movie heard last nite. Guess they want to watch it again? 2115z @49.990; TV audio shut off @ 2120z! Left a dead fading carrier @ 50.000MHz. 2145z dead carrier @ 50.010MHz

0050z 28 Feb 2012; distorted TV audio 49.715; Strong dead carrier 49.985...
0217z TV audio on 49.975; Strong dead carrier has drifted down to 49.970;
0218z distorted TV audio becomes somewhat readable on 49.710; Out sync cable sit com TV audio starts on 49.970; two seperate TV audios are now heard; thus the TV audio on 49.970 signal drift toward six meters begins....
0230z TV audio on 49.975....
0240z TV audio on 49.980...
0300z TV audio on 49.985...
0305z TV audio on 49.990...first sit com ends, Warner Brothers logo tune, second sitcom starts...
0310z on 49.710, program switching, music loops , then no audio just clicks, then very distorted TV audio, then gone
0315z TV audio now on 49.995...
0317z 49.710 very distorted audio, series of beeps than off
0318z 49.710 back on, very distorted TV audio
0320z TV audio on 50.000... anyone's guess what the upper frequency will be tonite.
0325z TV audio on 50.005...
0325z audio stops in mid show
0327z dead carrier @ 50.010MHz
0333z dead carrier @ 50.015MHz... with audio stopped looks like this is the upper tonite.
0405z dead carrier dropped to 50.010MHz
0415z dead carrier drops to 50.005MHz
0425z weaking dead carrier reaches  50.000MHz...
0427z 50.000 dead carrier comes back up...TV audio starts again, switching channels, on OTA channel w/ 1" live (cable network)delay.
0435z slight downward drift to 49.995...
0445z drifting toward 50.000...
0512z TV audio @ 50.005...
0537z TV audio @ 50.015...
0539z 50.015 cable movie ends Warner Brothers logo tune
0540z 50.015 music loop... sounds like channels switching?
0543z 50.015 adult cable program...foul language
0548z audio stops then dead carrier on 50.015...
0601z 50.015 TV audio starts again, switching, sounds like another 18+ show or movie...
0610z TV audio @ 50.020...
0620z TV audio @ 50.025...
to be continued...

Like clockwork the 1330z local sunrise news show has started up, based on the predicted shut off at 1500z, signal will likely just reach the band edge again.

0047z 29 Feb 2012; cable sit-com TV audio 50.000...
0049z cable sit-com TV audio 50.005...
0051z cable sit-com ends, music loop, another version of the same sit com starts...
« Last Edit: February 28, 2012, 04:56:58 PM by KB7WOX » Logged

Posts: 56

« Reply #7 on: February 28, 2012, 05:02:05 PM »

If it is, can't figure how its connected to the TV audio and how it can have an output to give metal street light poles to act like antennas over an area of one mile!

0105z 50.010 TV audio sit com is commercial free...
0113z 50.010 sit com ends, Warner Brothers signoff tune, same sitcom starts again as a repeat...
last sit com run time 22(')minutes, run time as commerical free...
0120z 50.015 TV audio...
0126z 50.015 heard a tiny .5(")second pause, suggesting an ongoing recording or a pre-recorded TV show...
0135z 50.015 sit com ends, running time 22', Warner Brothers signoff tune, another of the same sitcom starts again...
0140z 50.020  sit com TV audio... should end at 0157z...
0149z 50.025 heard a tiny .5(")second pause again...
0218z 50.025 sit com ends, running time 22', Warner Brothers signoff tune, another of the same sitcom starts again...
0218z 50.025 random audio changes, not sure if its a kid's movie or what it is...
For any six meter hams traveling on Sunset Hwy near Bronson Creek listen for a kids movie TV audio on 50.030
0349z 50.035 yogi TV audio, on cable or pre-recorded?
0402z 50.035 yogi class audio stopped...
0403z 50.035 channel switching thru cable, OTA audio...
0405z 50.035 stopping to look, then switching on...
0407z 50.035 found something to watch...
0409z 50.035 TV audio stopped, dead carrier...
0411z 50.035 audio started with same sit com music loop heard earlier, music loop repeating over and over...
0413z 50.040 sit com music loop repeats then stops then starts then another episode of the same sit com audio starts...
0417z 50.040 sit com audio stops, music loops, than another episode of the same sitcom starts... it appears they are surfing thru a pre-recorded sit com show, because the audio stopped again at 0419z and now its a dead carrier again...
0424z 50.040 sit com audio starts again, what is going on during the dead air periods? Fast forwarding or rewinding must be a disconnection with the audio but not with the signal...
0435z 50.040 audio stopped, dead air, sounds like a rewind the audio picks up at an earlier point of the show...
0445z 50.040 sit com ends, Warners Brother tune, dead air, another repeated episode of the same sitcom starts...
It looks the upper frequency has been reached tonite 50.040...
to be continued...
Like clockwork started up at 1330z of the local sunrise news show, and the shut off coming at 1506z, I little later then normal, the carrier signal then drift up and over the band edge.
« Last Edit: February 29, 2012, 09:21:17 AM by KB7WOX » Logged

Posts: 1209

« Reply #8 on: February 29, 2012, 04:45:27 AM »

Sounds like one of those in-home cable TV extenders that use the home wiring for a cable. This if on a subscription or "TIVO" recorded series of shows would give this type of output. Probably output to an older analog TV. Only the FM audio would be audible and since the video is about 4.5 MHz away that signal might not be heard as noise either.


Posts: 7718

« Reply #9 on: February 29, 2012, 12:25:43 PM »

I think we agree that the source is a Tivo-like video recorder. Now you get to track it down and deal with the owner.

Posts: 56

« Reply #10 on: February 29, 2012, 02:12:49 PM »

Agreed, tracking down this box is going to be the tough part, especially if they are using in-house wiring as an antenna. Can try using the street light posts again, but I’m not too hopeful for any more good results.  
Called the local sunrise news channel people today, to suggest having them send a message to the box owners, saying if you own a TV extender or TiVO like box near my qth, which is connected to house wiring to call the station and their name & address would be passed on.  The station staff said no, too confusing to the viewers. Kind of concur, don’t want every nut case in the viewing area banging on my front door with more false leads.  
All I can do for now is to issue a:
 “RFI Warning”  for all hams traveling in or living in a one mile (1.5km) vicinity of US 26 (Sunset) Hwy and Bronson Creek to be aware they can expect to experience, drifting TV audio interference in the 50.000 to 50.040MHz range at 0530LT to 0700LT, randomly during business hours and at 1600LT to past 2300LT nightly from an unlocated device.

de kb7wox

« Last Edit: February 29, 2012, 02:24:28 PM by KB7WOX » Logged

Posts: 1209

« Reply #11 on: February 29, 2012, 02:43:40 PM »

Reverse (perverse) RFI location technique. Generate the strongest CW or allowed digital siganal in that part of the band and go fish for 6 Meter DX during the times when the interference is noticeable. If you signal is strong enough you should create enough noise to get noticed and they will have to do something about their noise problem.


Posts: 7718

« Reply #12 on: February 29, 2012, 05:35:50 PM »

Two direction bearings using a portable dipole on a 10' mast should point you to it. 

Posts: 56

« Reply #13 on: March 03, 2012, 03:21:25 PM »

So far the folded dipole on a portable pole gives a confused signal field but a good signal strength, with some tweaking and additional practice it looks like it will work.

« Last Edit: March 06, 2012, 05:09:28 PM by KB7WOX » Logged

Posts: 39


« Reply #14 on: March 12, 2012, 10:55:33 AM »

If the folded dipole gives a "good" signal strength, try putting a 10 or 20 dB attenuator in the feedline. You will get much better nulls that way. In DFing, sometimes it's better to use the nulls than the peaks. Go around town and get at least six readings from different locations, and plot those as accurately as you can on a map.
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