AM Broadcast Spectral Components

Quitle likely plain old hum :-)

Seriously, local stations can generate a lot of level on house wiring, get modulated at all sorts of cheapo power supply rectifiers and then re-radiated. Had it many times. In the US you'd mostly see 60Hz, 180Hz and so on. In Europe 50Hz and 150Hz.

You can't really have much in terms of little sub-audio carriers because most AM radios would make that annoyingly audible. Also, the audio frequency response of an AM channel is something like 40Hz to 5kHz anyhow.

--
Regards, Joerg 

http://www.analogconsultants.com/

Up here in Canada, we call frequencies in the 100 to 300 Hz range "bass".

Due to frozen vocal cords ?>:-} ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
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| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

Bah Humbug (T'is the season).

signals at between 100 Hz and 300 Hz away from the carriers, below the main program audio. I have called a couple stations to ask what these signals are, but they haven't called me back.

used for low-speed remote signaling, and there's OFDM, but I didn't think they are in use in the US. There's also a Nielsen TV rating signal that's sometimes used in the US.

Not used in the US.

Nielsen does use sub audible data but most of the energy is below

150Hz. Maybe, but it doesn't look like your spectrum analyzer plots.

spectrum plots are posted here:

870KHz is KRLA 710KHz is KSPN Neither is broacasting AM stereo (HD Radio), so that's not the cause.

Lots of possibilities. Spurs generated in your spectrum analyzer.

60/120 Hz hummmm. Synthesizer phase noise in the exciter. Spurs and junk added across the STL (station to transmitter) link or over whatever fiber or copper is being used. Intermod mix in your spectrum analyzer from nearby transmitters. Secret sub-carrier used to communicate with Area 51.

Fire up an RF generate on the above frequencies at the same level as the radio stations and see if the display is clean.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Sounds fishy to me:

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

That's only for the East-coasters...

signals at between 100 Hz and 300 Hz away from the carriers, below the main program audio. I have called a couple stations to ask what these signals are, but they haven't called me back.

used for low-speed remote signaling, and there's OFDM, but I didn't think they are in use in the US. There's also a Nielsen TV rating signal that's sometimes used in the US.

spectrum plots are posted here:

Huh?? I see nothing unusual about either of those spectrum plots.

More likely due to frozen nuts...

HD (IBOC) is in the guard band, i.e outside the main AM signal. IBOC stands for In Band On Channel, but really it is on the channel of another station that used to be protected.

I don't know if it still lives in cyberspace, but there was a weird signal coming out of the Nevada Test Site in the early 90's or maybe late 80's. When it was traced to the NTS, the signal stopped. No explanation was given. IIRC, it was in the 800 to 900 range. Art Bell mentioned it on Coast to Coast, so that might pin down the time frame. You could hear it on the skip in California.

I was thinking it might be a weird plasma etcher of some sort,but they use ISM frequencies. Usually 13.56MHz. When Triangle Machinery and RA Associates were still in business, these ISM RF linears were on the surplus shelves. This predated RFID, but still, what would you do with one?

13.56 MHz is still used for diathermy, NMR, induction heaters, fruit dryers, plastic injection molding pre-heaters, sterilizers, etc.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Not ALL Canadians are nuts!

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I wondered about it being hum. But the envelope looks more like the should ers you expect from data modulation rather than line frequency spikes, and they do not occur at exactly 60 Hz or multiples. And -35 dBc is pretty lou d for incidental hum. Also they don't appear to vary with the main audio m odulation either, based on repeated observations.

George

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oulders you expect from data modulation rather than line frequency spikes, and they do not occur at exactly 60 Hz or multiples.  And -35 dBc is pret ty loud for incidental hum.  Also they don't appear to vary with the main audio modulation either, based on repeated observations.

well what does the station SOUND like?

you would easily be able to hear this

Mark

"Mark"

well what does the station SOUND like?

you would easily be able to hear this

** Hey - don't spoil George's perfectly good troll with a sensible question.

.... Phil

In one plot it looks like 60, 180 ... Hz, the other looks like 120Hz and harmonices which you'd have with older single-dide rectifiers. Because that results in even-order harmonics. The spectral width depends on the load. For example, if this comes from uncle Leroy's old TIG welder while he is welding it'll be pretty wide.

Pretty normal in some situations. Often it is louder on local stations than on distant ones.

Hum modulation usually doesn't. Its amplitude and spectral constellation depend on the load that's on the offending rectifier. In the old days it was easy to find out the offender by unplugging one device after the other. Today that's almost impossible because there is so much of it and some stuff needs elaborate re-programming after unplugging, such as the VCR.

--
Regards, Joerg 

http://www.analogconsultants.com/

That's an interesting component, a dipole or other antenna that's periodically shorted at the feed point, by a diode or some other sort of switch. It becomes a modulated reflector. Of course, any house is full of them.

[...]

European shutters could drive people crazy that way. The expensive kind is not plastic but aluminum. Crackle .. ka-crackle ..

In the days of NTSC you could get some really interesting effects when placing an ancient metal-blade fan in the path. With DTV you'll just get the usual frozen Picasso or blue screen.

--
Regards, Joerg 

http://www.analogconsultants.com/