1521 Mystery Solved?

[ChrisSmolinski]

A mysterious carrier has been observed on 1521 kHz the last few days, I posted some waterfalls in a previous thread: http://www.hfunderground.com/board/index.php/topic,23633.0.html

Earlier today, Bruce Conti posted the following on the DX'ing Facebook page:

Another hypothesis: I've also been receiving an unID signal on 1559 kHz producing a het against 1560 New York. Is it possible that both 1521 and 1559 are spurs at +/- 19 kHz from 1540 transmitted by a North American radio station on 1540 kHz? I received both 1521 and 1559 kHz signals this morning, but still no audio. 1540 transmitter spurs would explain why both 1521 and 1559 seem to be open carriers.

So I went back to a set of SDR I/Q recording files I made on 28 September 2015, and generated high resolution (8 million point FFT) waterfalls for 1521, 1540, and 1559 kHz. You can see exactly the same carrier present on 1521 and 1559 kHz. You can also see likely candidate station on 1540 kHz that has a similar pattern, and fades out the same time. On the 1540 plot, it is the red trace closest to 0 Hz at the very bottom of the waterfall. I think Bruce nailed it.

1521 kHz:


1559 kHz:


1540 kHz:

[atrainradio]

WNWR 1540 is in Philly. Betcha it's that guy. 50kW daytimer

[William Hassig]

Does this station simulcast an FM station? Plus and minus 19khz looks like feeding a mono FM tuner without the 75µs deemphasis directly into the audio input of the AM transmitter. Decades ago I modified an FM converter for the AM radio in a used car I had by removing the deemphasis. The converter put out an AM signal on 1400 kHz and also the stereo pilot 19khz above and below that. I also was able to slope demodulate SCA subcarriers 42 and 67 kHz away from 1400 kHz. Driving along in Chicagoland listening to muzak in the car was weird. Stereo DSB difference subcarriers 38khz away sounded like crap.

[Kilokat7]

I think this mystery was solved months back and it was generally accepted that the Bahamas on 1540 was (still is?) the culprit.