I clean office buildings at night and have a Panasonic pocket radio I listen to. Tonight the FM band stopped working. All I get is flat static. AM works fine. I had another radio, different manufacturer, do the same. I just don’t get how one band can stop working. I changed the batteries too, btw. To no avail.
FM and AM refer to the modulation technique, but we know you mean the band of 88 to 170 Mhz allocated to FM radio. (AM radio is 800 to 2000 kHz … approx)
So there are two things different between them
- The frequency
- the modulation technique,
otherwise much the same
Now with AM, there is only weak noise immunity, but it can only be jammed with a very powerful signal… a signal more powerful than the power of the radio station coming through the walls…
But with FM it has good noise immunity , but it can be jammed if the discrimator cannot track the carrier moving in frequency. So it can ignore a bit of noise, but medium noise just kills it.
Whether that is done by accident or on purpose, there is a noise source in the building that is causing the discriminator to fail to track the FM carrier. Its like blinding lights distracting you, its being mislead …
Its of course possible that the noise is specifically in the FM band not the AM band, but there is a reason a wide frequency noise source would block FM modulation not AM modulation.
Your radio has an FM part and an AM part. It’s not like you’re just shifting bands, you are, as Isilder described, shifting to a completely different way of encoding the signal. It’s unsurprising that one of these parts can malfunction while the other one keeps working.
OP did mention the problem on two different radios, so I don’t think it’s an equipment failure.
FM and AM are different modulation types, but as far as music on the radio goes, they are also located on different slices of the radio spectrum. My guess for what is killing his radio is RF interference from inside the building, presumably hitting the portion of the VHF spectrum that FM radio stations broadcast on (or at least, it’s a type of interference that hits FM modulation worse than AM modulation).
If I were to bet money, I’d say it’s an electrical short, or maybe a cheap/malfunctioning light fixture in the building. As it happens, I saw an article about this yesterday where marijuana grow lamps were causing all kinds of interference for local ham radio operators.
There was another story I read a few months ago about a shorting neon storefront sign dropping the hammer on all radio communication in an entire city block (police radios, cell phones, etc.) Not sure how you’d pin down the source without investing in a spectrum analyzer or bringing some of your local hams to work with you.
EDIT: You might consider passing a word along to the building’s maintenance people. They might want to know if they have a lighting fixture on the fritz causing RF interference, since that’s against FCC rules (yes, the FCC cares if you accidentally create a radio station, though they’re unlikely to send in the SWAT team). If they get complaints from other employees about similar problems, they might be able to chase the problem down on their own time.
One design element to consider is that some AM/FM radios can use different antennas for the two bands. If there’s a weak circuit connection (e.g. corrosion, trace break, disconnected wire) to the FM antenna, the AM tuner would still get good signal from its antenna.
But as mentioned earlier, FM requires a stronger signal than AM to decode correctly (i.e., more likely to break up below intelligibility at low signal levels).
Is the loss permanent or does the FM start working when you leave the building? I’m under the impression that it’s permanent, which rules out interference.
It might be helpful to know the model of radios. Some have an internal AM antenna and an extendable FM antenna so even breaking off the antenna wouldn’t affect AM. Some use the headphone cord as an antenna.
This triggers a burst on my irony meter, seeing that ham radio operators have often been a source of interference affecting neighbors’ over-the-air TV reception.
One thing the OP doesn’t mention is if the FM works outside of the building, or does he only have a problem while working inside. If he can pick up FM outside of the building, we can rule out the radio being on the fritz. If the radio doesn’t work only when he’s inside, then yes, electrical interference probably is the problem.
I see Fubaya has already addressed this, so just call me Captain Redundant. :smack:
Given that over-the-air TV and ham radio operate on different frequencies, this shouldn’t be the case, but sometimes is due to malfunctioning equipment (sometimes feedlines will resonate in unexpected ways). Considerate hams should take measures to correct such problems when it’s brought to their attention, of course.
What’s unusual, office buildings are notorious for killing AM reception, especially with lots of flourescent lighting, computer power supplies, etc. FM is far more tolerant of this kind of thing, mostly due to a lot higher IF.