How did this happen? FM Radio Station picked up by my scanner (UHF Ham Frequency)

[D31245]

A strange phenomenon happened this morning with my scanner.

While in the bathroom getting ready for the day, I had my C.Crane CC Solar Observer tuned to a local Boston FM Classical Radio Station (99.5 WCRB) and my Bearcat BT125AT scanning the Ham service frequencies.

Several times, the scanner stopped on 441.0500 and simulcast (or picked up) the FM music station that I had playing. If I adjusted the tuner or shut off the radio, the scanner would cease broadcasting that station. The radios were about 4 feet apart.

I’m sure there’s an explanation and would appreciate if someone could explain how this happened?

 

[nd5y]

Probably a harmonic of the local oscillator in the FM radio.

 

[a417]

Part of the RX path (local oscillator, maybe?) of the CCrane is transmitting strong enough for the scanner to recieve it.

Happens all the time.

 

[nd5y]

441.05 ÷ 4 = 110.2625
Assuming the radio has 10.7 MHz IF and high side injection like most do:
110.2625 - 10.7 = 99.5625

 

[D31245]

This is interesting. Thanks for the explanations.

This also jogged my memory and I recall radio stations coming through my guitar amp occasionally in the 70’s. I cant remember if it was AM or FM. I don’t remember if my electric guitar - interacting in proximity to the amp, or maybe a microphone - was causing it.

Interesting phenomenon nonetheless!

 

[ecps92]

This is interesting. Thanks for the explanations.

This also jogged my memory and I recall radio stations coming through my guitar amp occasionally in the 70’s. I cant remember if it was AM or FM. I don’t remember if my electric guitar - interacting in proximity to the amp, or maybe a microphone - was causing it.

Interesting phenomenon nonetheless!

Not a Phenomenon, but as Tom (ND5Y) calculated, basinc RF Electronic principles of how radios actually work
It can work to a disadvantage, but can also be used to remove interference by calculating the different and tuning to the new Freq

Lining up here in New England with T-Band, so many of the scanner had to listen to Boston Fire of 483.1625 up in the 504 band to eliminate the Business band users being heard in thr 483 channels that were actually in the 461-465 band

 

[wtp]

21.4 the old magic number.....

 

[tvengr]

21.4 the old magic number.....

Except older Uniden scanners which used 10.8 IF. When TV was analog, I used to listen to channel 2 audio by setting my Bearcat 210 to 38.16 MHz. The aural carrier frequency was 59.76 MHz. The visual frequency was 55.26 MHz which was offset by 10 KHz from the standard 55.25 frequency to avoid a venetian blind effect for viewers between Baltimore and WCBS in New York. The aural frequency also needed to be changed to maintain the 4.5 MHz intercarrier spacing between the visual and aural transmitters.

 

[wtp]

i was a radio shack guy at the time.
i still remember doing the math for cell reception on a pro-34
it was 800/2 +16.05=
so 888/2 (444) +16.05 = 460.05
verified by my pro-2004 it was close enough.
the 16.05 is 3/4 of 21.4

 

[tvengr]

That was back when cell phones were analog. There isn't even a reason for blocking cell phone frequencies in scanners any longer since they cannot be monitored anyway. I have scanners which covered cell phone frequencies before the band was blocked in later scanners.

 

[ecps92]

Except older Uniden scanners which used 10.8 IF. When TV was analog, I used to listen to channel 2 audio by setting my Bearcat 210 to 38.16 MHz. The aural carrier frequency was 59.76 MHz. The visual frequency was 55.26 MHz which was offset by 10 KHz from the standard 55.25 frequency to avoid a venetian blind effect for viewers between Baltimore and WCBS in New York. The aural frequency also needed to be changed to maintain the 4.5 MHz intercarrier spacing between the visual and aural transmitters.

One of our Fire Dept's was /still is on 483.5375 and even their GE radios got images, they regularly had to ensure the Apparatus and Pump Operator did not have "Off Hook Monitor" otherwise they had the local UHF TV Channel (38) - might have been good if the Boston Bruins were still on that channel, but by then had migrated to the Cable channel of NESN (Nope - not Northeast Scanning News )