Squealing and foreign languages

[vchimpanzee]

What's going on?

This morning I couldn't hear Paul Harvey half the time!

When I lose him I hear this sound like in the movies or on TV when characters try to tune their AM radio. Then there's some kind of foreign language.

 

[schmave]

Well first off this post is missing several fundamentals:
- Where are you?
- On what station were you hearing this broadcast?
- What time was it? You said this morning, but with critical hours, etc. even less than one hour can make a big difference.
- Is this a common phenomenon where you are?

 

[vchimpanzee]

I'm in North Carolina, and on most mornings I get a clear enough signal from this station. There is some interference from other stations on the same frequency, but not that often. This squealing mess is rare. I'm pretty close to the edge of where you can hear this station clearly, but it's my only option for Paul Harvey.

On another clock radio, I discovered I couldn't pick up anything but strong stations in the morning, and everything else sounded like public radio or was broadcast in a foreign language. I have the same problem on a conventional radio for everything above about 1400.

 

[BRNout]

Most clock radios are infamous for having just awful reception. Many (and I'd say well more than half) cannot even provide decent reception of local stations that you should be getting. By and large, they have crap tuners that smear local stations all over the dial and bleed strong stations over weaker ones.

They're pretty useless for the purposes of dxing. For example, I only use mine as an alarm clock or to tell me what time it is. You'll save yourself some headaches by getting a half decent radio.

 

[Grrrradio]

Are there a lot of electrical appliances in your house? Or did you perhaps leave a computer monitor on and forget about it? Those are particularly bad for RF-noise annoyance.

Then again, one other possibility suggests itself. Though your use of a (most likely not very sensitive) clock radio argues against this being the case, the squeal, foreign languages, and your near-coastal location raise the possibility that you're hearing a "heterodyne" tone (or het for short.) These often owe to international AM stations coming in and mixing with U.S. stations on nearby frequencies. Many international stations are on 9 KHz multiples, rather than the 10 KHz on which the U.S. system is based. If the difference between the frequencies of the two stations is within the audio bandwidth of the AM broadcast signals your radio is designed to receive (i.e. less than 5 KHz), your receiver will see a "mixing product" of these signals.

AM works in kind of an oddball way. Audio amplitude and RF "amplitude" (i.e., signal strength) vary directly with each other -- and amplitudes, by their very nature, are additive. When amplitudes within the audio frequency range are present on radio wave(s) of the frequency you're tuned to... your receiver sees them all at once, without respect to which signal they happen to be coming from. (By contrast, FM receivers kind of "track" the phase variations of incoming signals, because they're designed to detect only frequency shifts... this is what allows them to "capture" a stronger signal over a weaker one.)

These oddball physics have three practical consequences for AM radio:
1) The "all at once" thing is part of the reason AM is so susceptible to power-line noise -- power traveling in a power line oscillates at 60 Hz, which is in the audio frequency range, and something about the transmission also generates RF signals at AM broadcast frequencies -- so when you get close to a power line, your radio hears "AM station PLUS 60 Hz buzzing crap."
2) The fact that "amplitudes are amplitudes are amplitudes" also means that when the RF signal gets weaker, the audio you receive gets quieter. (On FM, you get roughly the same volume of audio when you try to listen to a weak signal... you just get some static across it as an artifact of the receiver trying to extract 100% of the audio from 60% of the signal that it requires for full fidelity. That static is the audio equivalent of the minus-40% your radio gets from trying to do that demented math. )
And -- of interest to us -- 3) the fact that "amplitudes are amplitudes are amplitudes" mean that mixing products which are inside the audio passband for AM receivers -- e.g. a 1 KHz signal resulting from a 1521 KHz station beating across a 1520 KHz station -- pass through the audio detector and get heard as audio tones. So you hear this annoying 1000-Hz squeal (or maybe 4000 Hz in the case of stations on 1404 and 1400 KHz.) If you happen to be musically trained and can recognize notes by their pitch, a 1 Khz squeal will sound like a flat version of the "C" two octaves above middle C... 2 KHz will sound like a flat version of the "C" three octaves above middle C. So that MAY be what your squeal is all about...

 

[BRNout]

Grrradio, with all due respect, do you really think he's picking up 1521 Saudi Arabia on a clock radio?!? :

I've never even done that with my super duper Sony 7600GR! Nor have I ever picked up anything else over here on AM from the eastern hemisphere - where the 9 kHz step is used.

The squeal is probably interference that results from the thing merely being plugged in. And, the foreign language is most probably Spanish - which is heard all over the AM dial almost everywhere these days.

No, vchimpanzee needs to get a decent radio. If cost is an issue, I would humbly suggest the analog Sony ICFS10MK2 pocket radio: http://www.jr.com/JRProductPage.process?Product=4030071 It's about $12 - cheaper if you shop around.

If you have a few more bucks, then go for this excellent Sangean: http://www.jr.com/JRProductPage.process?Product=19035

Both will eliminate the issues that vchimpanzee seems to have with his clock radio.

 

[vchimpanzee]

Are there a lot of electrical appliances in your house? Or did you perhaps leave a computer monitor on and forget about it? Those are particularly bad for RF-noise annoyance.

Then again, one other possibility suggests itself. Though your use of a (most likely not very sensitive) clock radio argues against this being the case, the squeal, foreign languages, and your near-coastal location raise the possibility that you're hearing a "heterodyne" tone (or het for short.) These often owe to international AM stations coming in and mixing with U.S. stations on nearby frequencies. Many international stations are on 9 KHz multiples, rather than the 10 KHz on which the U.S. system is based. If the difference between the frequencies of the two stations is within the audio bandwidth of the AM broadcast signals your radio is designed to receive (i.e. less than 5 KHz), your receiver will see a "mixing product" of these signals.

AM works in kind of an oddball way. Audio amplitude and RF "amplitude" (i.e., signal strength) vary directly with each other -- and amplitudes, by their very nature, are additive. When amplitudes within the audio frequency range are present on radio wave(s) of the frequency you're tuned to... your receiver sees them all at once, without respect to which signal they happen to be coming from. (By contrast, FM receivers kind of "track" the phase variations of incoming signals, because they're designed to detect only frequency shifts... this is what allows them to "capture" a stronger signal over a weaker one.)

These oddball physics have three practical consequences for AM radio:
1) The "all at once" thing is part of the reason AM is so susceptible to power-line noise -- power traveling in a power line oscillates at 60 Hz, which is in the audio frequency range, and something about the transmission also generates RF signals at AM broadcast frequencies -- so when you get close to a power line, your radio hears "AM station PLUS 60 Hz buzzing crap."
2) The fact that "amplitudes are amplitudes are amplitudes" also means that when the RF signal gets weaker, the audio you receive gets quieter. (On FM, you get roughly the same volume of audio when you try to listen to a weak signal... you just get some static across it as an artifact of the receiver trying to extract 100% of the audio from 60% of the signal that it requires for full fidelity. That static is the audio equivalent of the minus-40% your radio gets from trying to do that demented math. )
And -- of interest to us -- 3) the fact that "amplitudes are amplitudes are amplitudes" mean that mixing products which are inside the audio passband for AM receivers -- e.g. a 1 KHz signal resulting from a 1521 KHz station beating across a 1520 KHz station -- pass through the audio detector and get heard as audio tones. So you hear this annoying 1000-Hz squeal (or maybe 4000 Hz in the case of stations on 1404 and 1400 KHz.) If you happen to be musically trained and can recognize notes by their pitch, a 1 Khz squeal will sound like a flat version of the "C" two octaves above middle C... 2 KHz will sound like a flat version of the "C" three octaves above middle C. So that MAY be what your squeal is all about...

I have no computer at home.

The phenomenon happens on a Radio Shack table radio too, above about 1400.

I don't have the money to buy a "decent" radio.

I'm 200 miles from the coast; does this make a difference?

 

[vchimpanzee]

The squeal is probably interference that results from the thing merely being plugged in.

I don't hear it at all most mornings. Today, I could clearly hear the preacher talking about how God showed mercy to Sodom and Gomorrah or someone because of Abraham. I think that's it. Anyway, I didn't want to hear him so I turned it off this time.

 

[vibe]

AM radio IS unpredictable to say the least. In Fla I would hear 2 (and once 3) stations on the same frequency a number of times. On I-75 between Ft. Myers and naples I had a very strong, city grade quality signal on 620 St. Pete with a very weak (but consistent spanish speaking station. This happened on many other frequencies in S. Fla but this one I remeber well becasue I was slightly annoyed until my mind could tune out the 2nd station.
On 1650 I had both Radio Disney in VA and a station from Ft. Smith. Not often but at sunset.
On 1030 I had religious stations from NC and TX battling it out with a much stronger spanish speaking station.
But from what I found the only consistent thing about AM radio Is it's changing reception.

 

[amfmsw]

"Squeel"?...sounds like heterodyning. And if the top end of the unit is pretty much dead, it sounds like an improperly "trimmed" antenna.

 

[flytrap]

Here is another possible cause. Some cheaper radios have a bad habit of picking up shortwave by mistake. I discovered my moms clock radio would occasionally pick up radio canada and radio havana cubu when I was a kid, I thought I was losing my mind since I'd never heard shortwave radio. I have a grundig s350 radio that has shortwave bleeding in all over the AM band which also causes the whistles. Most of the time it's Habana Cuba shortwave thats bleeding in. Cuba also has several blowtorch AM stations that cause havoc on AM at night. WJNT 1180 in Jackson, MS had to add a nightime FM because you could barely hear them out of the parking lot when Castro cranked up the flame thrower.

 

[vchimpanzee]

Shortwave was my guess. It's been happening for years.

Actually, I never used to have to listen to this one AM, but if I got off of the strongest one, which I was listening to in 1994, this is what I believe happened.