pagers on 263.300 nfm ??????
- Thread starter burts
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jb872033
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are you close to a pager transmitter? you might be getting a mirror or something?
JB
JB
burts said:
An image is an unintended consequence of the mixing process in a receiver. If the receiver has a 10.7 MHz IF, for example, to receive paging on 152.0 MHz, the local oscillator could be at 141.3 MHz. 141.3+10.7=152.0 - that's how it works. The 'image' frequency would be the local oscillator 141.3 - 10.7, or 131.6. That's just an example to show what an image is. Scanners usually have a pretty strong image response. It takes filtering in the front end, and image reducing mixers to eliminate it - all design features in a good receiver. Scanners DO NOT have "good" receivers.
There's a variety of reasons why you could be hearing paging there, but the most likely is an intermod mix, not an image. It wouldn't likely be double the frequency, but it could be double the frequency, plus or minus the frequency of another signal. That's just one of many mechanisms that could cause that. If you know what's actually happening, you can usually make mathematical sense of why something is being herd on some odd frequency, but you have to know everything that's involved. In this case, you only know the result.
If you're running a preamp, you may try removing it to see if it goes away. It could be mixing several strong signals and causing a local paging signal to be heard at 263.3 MHz.
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Images were a common problem with older single conversion receivers but today double and triple conversion is employed pretty much eliminating image signals.
"Dirty" pagers are pretty common, they're one of the most notorious sources of spurious emissions commonly known as spurs. This is one possibility, another is front end overload not necessarily from the offending signal. This common phenomenon is intermodulation distortion known as intermod. This topic has been discussed to death so I suggest reading previous threads rather than beating this long dead horse to dust.
"Dirty" pagers are pretty common, they're one of the most notorious sources of spurious emissions commonly known as spurs. This is one possibility, another is front end overload not necessarily from the offending signal. This common phenomenon is intermodulation distortion known as intermod. This topic has been discussed to death so I suggest reading previous threads rather than beating this long dead horse to dust.
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