Does a scanner have a slight range on a frequency

gpsruler

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I am really new to this scanning and scanner stuff. I was playing with my scanner the other night and picked up 155.7350, it skipped and kept going. It sounded like there was something there, but it was gone before I could get good ears on it. There is a local sheriff that uses 155.7300MHZ.

So my newbie question is: Can a scanner or frequency be off by that much 5kHz and still pick up good audio? I get little results when searching to identify 155.7350, but a ton in the 155.7300 searches.

Thanks in advance.
 

nd5y

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So my newbie question is: Can a scanner or frequency be off by that much 5kHz and still pick up good audio?
Yes that's normal. It's because of the receive bandwidth, transmitted signal bandwidth, receiver tuning steps and assigned channel spacing.

An NFM signal occupies up to11.2 kHz bandwidth and an FM signal occupies up to 20 kHz bandwidth.

The receiver bandwidth has to be wider than the transmitted signal to make up for the transmitter and receiver not being exactly on frequency. For a scanner this is probably 25 kHz or more.

That means your receive frequency is centered in a 25 kHz wide window but the tuning steps might be as small as 2.5, 5, 6.25 or 7.5 kHz depending on the the type of receiver.

Most non-federal stations in the 150-162 MHz band are assinged on 7.5 kHz spaced channels. That means that adjacent channels overlap because they are 11.2 kHz wide but only 7.5 kHz apart.

The average scanner can receive NFM stations up to around 7.5 kHz off frequency and if the signal is strong you might not be able to tell any difference.
 

majoco

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Yes but the OP said 155.7350MHz compared to 155.7300MHz - that's 50kHz apart. I doubt that any scanner would resolve one of those frequencies when tuned to the other - unless it was a 'receiver' rather than a scanner and was set to WFM as in broadcast FM. AFC of course may be able to 'pull' a station away from its apparent frequency.
 

IAmSixNine

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I put in a request with IBM to use the super computer to crunch these numbers and hopefully after that we can no longer worry about math.
I gave up years ago trying to figure out who the alligator wants to eat if 1<5 or 1<5 man I was never good at math.
 
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gpsruler

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Thanks everyone for your input. it helped a lot in learning more about this. and math... haha
 

WB9YBM

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Niles, IL
I am really new to this scanning and scanner stuff. I was playing with my scanner the other night and picked up 155.7350, it skipped and kept going. It sounded like there was something there, but it was gone before I could get good ears on it. There is a local sheriff that uses 155.7300MHZ.

So my newbie question is: Can a scanner or frequency be off by that much 5kHz and still pick up good audio? I get little results when searching to identify 155.7350, but a ton in the 155.7300 searches.

Thanks in advance.
It'll pick up an adjacent frequency (depending at least in part how strong it is, and the scanners' ability to reject off-frequency signals), although receiving it with well is debatable...
 
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