I'm studying for my Technician license, and listening in to HF, VHF and UHF bands just to get a feel for how to work with frequencies, squelch, antennas, etc. Had something happen today that I couldn't explain. I was doing a scan through the 70cm band, running from 400MHz to 480MHz, and at 450.040 I picked up a local AM radio station. I checked the radio station website and they only broadcast on 1520 KHz. How did I receive that signal on such a different frequency? I wasn't even working with a very powerful antenna, just a Baofeng UV5R. My first thought was that perhaps the local signal was just so powerful it overcame my radio reception. But if that's the case, why did it happen just on that one frequency? I was scanning other frequencies through the day and didn't have it happen on any other frequency. I also checked to see if we had any nearby repeaters at that frequency but we don't; nearest frequency for a regional repeater is 444.9750. Thanks.
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7$\begingroup$ Maybe you received a UHF FM link from the studio to the transmitter site. $\endgroup$– JuanchoAug 14, 2016 at 13:36
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$\begingroup$ Juancho makes a good point. Were you receiving the signal with AM or FM? $\endgroup$– JSHAug 15, 2016 at 3:11
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$\begingroup$ FM receivers can't detect AM. You may be interested to know that AM receivers can detect FM by slope detection (somerset.net/arm/fm_only_lowtech.html) $\endgroup$– user3486184Aug 18, 2016 at 19:52
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$\begingroup$ I picked up news talk 1080am of Hartford, CT on my baofeng uv5r+ tuned to 161.755 today. Which led me to this write up...I'm still confused $\endgroup$– AnthonyDec 13, 2016 at 16:39
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$\begingroup$ Probably mixing of frequencies in the receiver - for example the UHF studio link with a image of the IF frequency the output of which coincides with the frequency you are listening to... $\endgroup$– Old_FossilSep 13, 2017 at 5:05
3 Answers
at 450.040 I picked up a local AM radio station
I am sure you picked up a transmission
just a Baofeng UV5R
But not with that radio, or at least not AM
You either:
- Picked up a signal which is indeed AM, but then it would not be very distorted as the radio you are using only has FM (de)modulation.
or:
- Picked up something else.
If the audio received was not distorted (so then it must be FM), and clearly the same 'program' as the said AM station on 1520 KHz. Then it is very likely this is a "studio to transmitter link/feed" that you picked up. (as detailed in the comments already)
But to give you the official answer:
You are not picking up an AM transmission originally on 1520 KHz, on 450.040 MHz with an Baofeng UV5R radio. That would be quite impossible
:-)
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1$\begingroup$ Thanks for the replies. My radio has three bands - VHF, UHF and FM. I was on the UHF bands when I received the signal. We are positive it was a commercial radio station because we listened for over 10 minutes. Heard several songs, several commercials, and the station ID at least twice. We looked up the station online and they're only licensed to broadcast on that 1520 AM freq. I'll call the radio office and ask about whether they were broadcasting from a remote location,or if perhaps they use a different transmission frequency between the broadcast booth and the antenna. $\endgroup$– K. KerbyAug 17, 2016 at 19:29
I was trying to research some info and I came across your thread.
My guess is they took the audio output from the 1520 kHz tuner and fed it in the input of a 450.040 MHz transmitter. That's why it can be heard in the UHF region. In this way, FM or AM or frequency doesn't matter, because its only an audio feed from an 1520 kHz tuner. You could have listen to a 1520 kHz tuner and a 450.040 MHz tuner at the same time. There should be a delay between the two tuners, I would guess.
The 450-451 MHz band is often used by news media, broadcast TV and AM radio. They use it for communications between the station and the news vans, or between the station and the traffic helicopters. In addition, they use it for something called Interruptible foldback which is a stream containing the programming and occasionally commands from the studio to the "reporter on the scene". I hear these often, and it's just minutes and minutes of broadcast programming that suddenly stops.
I Googled and found some exact listings for the Boston media market - your area will have different frequencies but used for a similar purpose. http://scan-ne.net/wiki/index.php?title=Media_and_Fire_Buff
This can be handy to listen to, if you get traffic reports direct from the helicopter during rush hour!
