AM Station Drift

[Toomas Losin]

Here's a geeky story about interference.

I've been listening on 972 for Korea or Australia. Before the recent solar disruptions I did hear an oriental language but not more than a few seconds of intelligible talk or some music. To avoid CKNW on 980 I'm using lower sideband mode, as AM that close in frequency to a flamethrower is burnt to a crisp. I'm still getting some splatter on music peaks but that's mostly under control; other interference comes as a hefty 2 kHz het plus distorted audio whenever 970 fades up.

The interesting/geeky part about all of this is that I can see/hear *four* carriers on 970 using audacity as a spectrum analyzer. The question of the day is: What are they and what's the level of mutual interference wherever it is that they're actually audible? Two of the carriers are about 3 Hz apart, making an audible beat, another is 20 Hz lower than that pair, and the fourth is 25 Hz higher as well as being very weak. Assuming the carriers fade out at their local sunrise suggests the higher one is a few time zones east while the lower one is likely PDT. There is a mediumwave offset list on the net but I'm not sure how current it is; it suggests Ecuador for the higher one.

While looking at the spectrum with audacity I was pondering DXing solely by carrier. Surely government bureaucracies could be convinced that it's a good idea to require a digitally modulated ID on an AM
station's carrier to make a DXer's life easier?

[jon]

Here's a geeky story about interference.

I've been listening on 972 for Korea or Australia. Before the recent solar disruptions I did hear an oriental language but not more than a few seconds of intelligible talk or some music. To avoid CKNW on 980 I'm using lower sideband mode, as AM that close in frequency to a flamethrower is burnt to a crisp. I'm still getting some splatter on music peaks but that's mostly under control; other interference comes as a hefty 2 kHz het plus distorted audio whenever 970 fades up.

The interesting/geeky part about all of this is that I can see/hear *four* carriers on 970 using audacity as a spectrum analyzer. The question of the day is: What are they and what's the level of mutual interference wherever it is that they're actually audible? Two of the carriers are about 3 Hz apart, making an audible beat, another is 20 Hz lower than that pair, and the fourth is 25 Hz higher as well as being very weak. Assuming the carriers fade out at their local sunrise suggests the higher one is a few time zones east while the lower one is likely PDT. There is a mediumwave offset list on the net but I'm not sure how current it is; it suggests Ecuador for the higher one.

While looking at the spectrum with audacity I was pondering DXing solely by carrier. Surely government bureaucracies could be convinced that it's a good idea to require a digitally modulated ID on an AM
station's carrier to make a DXer's life easier?

I'd be interested in answers from those with actual AM engineering backgrounds, but I can't help wondering if you shouldn't be looking domestically for your 970 KHz "wanderers". With the large number of ancient AM transmitters around at poorly funded U.S. AM stations, I could easily see them being 3 to 25 Hz off frequency without attracting the attention of the poorly funded FCC Monitoring Office, if it even exists anymore. Even 25Hz is only a 0.0025% crystal calibration error at 970 KHz. A quarter of one hundredth of one percent.

[Eldon-Mr.CFAY]

Hi Everyone,
Yes thats quite interesting what you posted Toomas. Jon may be right on domestic station frequency drift in the USA by some stations. I don't think it happens too often but you never know. I was listening last Thursday morning about 1:30 AM and for the first time heard ZNS 1540 Bahamas here in Baltimore, Ontario. They were coming in quite well. When I turned the GE Superadio Two (which is what I was using upstairs in the house here at the time) to the west I got KXEL 1540 like a local here, very little fading at all. Actually ZNS 1540 had little fading too. They were talking about Carribean Islands etc. and sounded like slight British Accents etc. I always thought ZNS was 1545 khz. from past directories etc. however Mike and my 2012 World Radio TV Handbook tells me its on 1540. Power is listed at 8000 watts or 8 KWs. First time I heard them here in Ontario so was prety pleased about that. Mike told me that he has heard them in Toronto quite a few years ago and got them verified he thinks!!!! Why I mentioned this is because while listening to them it seemed like a whistling Het was near the frequency so I wondered if they might not be 1540 but 1545???? Perhaps what you said Jon about slight drifting of frequency by someone!!!! By the way last Thursday morning I noticed the Iowa AM stations were coming in well here, WHO 1040 blasting in with no slopover from 1050 Toronto (I am 60 miles east of them) and KCJJ 1630 coming in well from Iowa City too.

Anyway thought I would just add a few comments to this. By the way Jon do you remember all the talk about drifting MEXICAN AM stations on the broadcast band years ago in IRCA bulletin discussion!!!! At one point quite a hot topic! Don't know if the Mexican AM stations have improved the frequency stability a lot but probably some since then!

All the best, Eldon

[Toomas Losin]

Thanks Jon, I have no doubts that locals drift or are off-frequency. I was too-subtly griping about online lists of such stations being obsolete or incomplete. I did some further digging and found there is a DX subculture devoted to identifying stations by carrier offset. Right now I'm wondering what frequency has the most carriers on it; probably a graveyard channel. I'm not sure I'll ever try that as it's more fun for me to hear audio rather than just spot a carrier.

Eldon, congrats on hearing ZNS. At some point I'm likely to reverse the Pennant antenna so it's pointing at South America rather than Japan. Maybe I'll hear something more from the area than Cuba.