fM Radio Interference

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kb9hgi

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Im trying to listen to a P25 frequency on 851.875 and the only signal I get is from this Radio tower down the road. Its a College FM radio station I think . Its a tall tower with the light ontop and its about 3 or 4 blocks from me and all I hear is this darn thing no matter which scanner I use. Is there a way to block that signal from coming into my scanner. I tried ATT but that cut everything out.
 

paulears

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Google RF stub filters - pretty easy to make and you tune them to the unwanted frequency and they act as a notch. I suspect that the real problem with the very big difference between the broadcast frequency and the 800MHz frequency is that your receiver filtering is poor or non-existent. 100MHz at a distance wiping out 800MHz seems a bit odd. Perhaps some strange mixing with another local signal is going on?
 

marksmith

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A notch filter might help this, but that is one heck of an image problem from 100 mz to 800mz.
3 or 4 blocks away at that difference in frequency is a strange event. Especially when you consider college radio stations are low power.

536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others
 

ecps92

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Could it actually be a STL from 950 Mhz vs the Commercial FM 100 Mhz band ??
A notch filter might help this, but that is one heck of an image problem from 100 mz to 800mz.
3 or 4 blocks away at that difference in frequency is a strange event. Especially when you consider college radio stations are low power.

536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others
 

paulears

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ah - I see. Not one we use here, well - we do obviously have studio to transmitter links, but don't use the acronym. There's one from a radio station here in town to the TX site on 1.5GHz, and it's just listed in the Government data as 'link'.
 

kb9hgi

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I have a uniden 996XT and a uniden 996P2 and what Im trying to monitor is IL Starcom system here in Quincy, IL. There is 2 towers one in Quincy and one at Mendon The Broadcast knocks out the Quincy tower signal I can pickup the mendon tower but you will hear music coming in on the signal. What ever is on this tower I think is blocking signals. There is more then one thing on this tower then a couple block the other way is Sprint tower also. When the state police is in this area they can't get thru on their radios. So maybe Im SOL....lol
 

majoco

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The problem is probably cross-modulation or overloading of the RF stages of your radio. An FM band stop filter should reduce to problem to manageable proportions - google is your friend.
 

marksmith

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If the state police are having trouble, you would think there would be a complaint.

536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others
 

wa1nic

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It is entirely possible, being only a few blocks away, that said college station has some sort of spurious radiation at 851 MHz. A spectrum analyzer would be your best bet to be sure.
 

lmrtek

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Try a FM trap and see what happens

if that doesn't fix it, buy a 20 dollar SDR dongle and check for a dirty transmitter
 
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