question for the radio people

[Quantavious G]

a couple days ago the scan button on my radio captured a weak station on the am band. It's a cool station, plays a lot of stuff from the 40's and 50's. Problem is, whenever I get near powerlines the station takes a hit. Static and fade.

Why is am so affected by powerlines?

And no. Google is not my friend. It's not anybody's friend. I don't care enough to spend two hours researching radio trivia when one of you guy can tell me all I need to know in less than a minute.

 

[RKG]

Think of the emissions from broadcast radio stations as a sine wave. AM station encode the desired audio (the music you want to hear) by modulation (varying) the amp!itude (height) of the waves. Essentially, if you drew a line connecting the AM peaks, you would get a wave that looks like the music.

In the near field, high voltage electric transmission lines generate spurious radio noise. That noise "attaches" itself to the radio waves your AM radio is trying to listen to. This modifies the height of the apparent AM peaks. That is what causes the sound distortion.

FM radio, on the other hand, ignores the peaks. Desired audio is encoded by shifting the nominal FM frequency back and forth around the nominal center frequency. An FM radio looks only at the spacing at which the sine waves cross zero: high notes are closer spacing; lower notes are wider spacing. Radio noise from spurious sources is ignored.

Foregoing is a bit simplified, but I hope it answers your question.

 

[Quantavious G]

thank you

 

[appraiser]

AM radio picks up everything bad in the spectrum and tries to process it.

It has gotten worse over the years between florescent lights, crappy power supplies for everything under the sun, LED's, etc etc sending off crap and harmonics

 

[nickortizzle1035]

whats the station? id like to check it out

 

[Zappa]

Think of the emissions from broadcast radio stations as a sine wave. AM station encode the desired audio (the music you want to hear) by modulation (varying) the amp!itude (height) of the waves. Essentially, if you drew a line connecting the AM peaks, you would get a wave that looks like the music.

In the near field, high voltage electric transmission lines generate spurious radio noise. That noise "attaches" itself to the radio waves your AM radio is trying to listen to. This modifies the height of the apparent AM peaks. That is what causes the sound distortion.

This^

I'd also like to add that the AM receivers in most modern car radios are horrible.
The radio manufacturers look at AM as obsolete and don't bother spending much time to engineer good AM tuners. Then there's also the antennas, which by necessity, must be a certain physical length to do a proper job of receiving the low frequency signals of the AM broadcast band, which means it has to be longer than an FM antenna. If you notice most cars nowadays don't use the long fender mounted whip antennas anymore, instead they use a short "rubber duckie" antenna on the roof, or an even shorter one inside a "sharkfin" cover. Both of these types totally suck for AM reception.

 

[SS1]

Remember when I picked up a canadian station while driving a 67 polara flipping thru the stations..
If you want to know why, Take a long florescent light and walk under some power lines you will see the answer
That's how much bleed is coming off of them


View: https://youtu.be/5JGbT6m3Vv0

 

[n1bsbri]

Good explanations above on why AM is more susceptible to interference. I'll also add that the AM broadcast frequencies are also where power lines and such spew out most of their crap. Higher frequency FM bands don't have as much of a problem with that, plus the fact that FM is more immune to noise anyway (as described above).

 

[AHM]

Meh, weak.

 

[KBCraig]

Who remembers slope tuning?

Yes, I just dated myself... but we could get that signal juuuuust right.