Interesting find on 118.292

W1MSA

Newbie
Joined
Aug 22, 2006
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1
Location
Naples, Me
Can someone help me out with this one, while scanning through the air band in Maine I came across a local radio station (FRANK 107.5 FM) that can be heard quite clear on 118.292 on FM and just barley on AM as expected, the transmitter for this station is about 9 miles NE from my location and the RX frequency dose not appear to be a harmonic of the original.
 

MDScanFan

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Joined
Jan 23, 2010
Messages
184
Location
USA
That should be an intermodulation product of two strong Rx signals mixing in your scanner and producing an image above band. Based on those two frequencies you should have a strong broadcast signal around 96.7 MHz. Please check.
 

Ubbe

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Joined
Sep 8, 2006
Messages
5,126
Location
Stockholm, Sweden
I know that there's a mixing product in the scanner itself that I belive was around 10.8MHz higher of the received frequency and only in one frequency band. It needed to be very strong, something like 500uV and there was also another one at around 20.5MHz but required millivolt signals. It didn't get that mixing product below the frequency so it's something internal happening in the scanner. I tested all kinds of frequencies with a signal generator when I first got my BCT15 and only found those two frequency offsets that could be received. It probably are the same with the newer BCT15X.

I had it written down in a textfile that got deleted so I'm not sure of the exact frequencies but it is a phenomen that exists in all BCT15's and are easily cured by a FM broadcast trap filter.

/Ubbe
 

spanky15805

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Joined
Sep 18, 2004
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180
W1MSA, do you have a different air band receiver you can use? If the IM is still there, using the different receiver, then it's probably the FM station. Is the FM station on a site used by other FM stations? Could be that you are hearing the mixing product of a completely different station because the other station has a bad antenna, moisture in heliax or somebodies combiner has a problem. Get new batteries for the HT and start tracking. Once you figure it out, let the station know. They might be grumpy about it but they will fix it...eventually.
 

dlwtrunked

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Premium Subscriber
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Dec 19, 2002
Messages
815
That should be an intermodulation product of two strong Rx signals mixing in your scanner and producing an image above band. Based on those two frequencies you should have a strong broadcast signal around 96.7 MHz. Please check.
I did the same calculation. He has a station on 96.7 MHz with 15.5 kW ERP in Booth Harbor, ME not too far away.
 

wtp

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Joined
Apr 3, 2008
Messages
3,133
Location
Port Charlotte FL
my guess is the radio has an IF of 10.8
so instead of double the IF it is the IF difference and probably an overload of the front end.
 
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