How to determine if a nearby antenna is interfering with a scanner?

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Kumba

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So I moved to a new house, and I've noticed what once was pretty sharp reception from my county's public safety system has dropped to broken fragments with occasional motorboating. I suspect I might be stuck in the path of a large antenna about a 1/4th of a mile away, but I'm not sure what frequencies it's transmitting on to know if that's even the issue (and not say, simple coverage issues, since I know the county supposedly has issues in this area at times).

There a way to determine what the cause is by chance? I dug around in the FCC ASR database, and I think I found the particular tower (looks like a cell tower or something else), but nothing listed as far as the frequencies of any transmitters on it. Time to invest in a desktop discone or something more potent than a mobile handheld antenna? If it's this particular antenna, I figured there might be a filter or something I could attach to try and weed out the county's signal a little better.
 

DickH

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... Time to invest in a desktop discone or something more potent than a mobile handheld antenna? If it's this particular antenna, I figured there might be a filter or something I could attach to try and weed out the county's signal a little better.
If it's caused by that nearby tower, a better antenna will only make it worse. If your scanner has an attenuator turn it on. If it doesn't have an attenuator, try removing the antenna.
 

Kumba

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Was already here actually. It says there's both an FCC-registered antenna site and an unregistered cellular tower in the vicinity. I'll have to look around some more for the other antenna, but this first one is hard to miss.


If it's caused by that nearby tower, a better antenna will only make it worse. If your scanner has an attenuator turn it on. If it doesn't have an attenuator, try removing the antenna.
Removing the antenna causes the signal to vanish completely. Listening to the control channel directly (not the discriminator tap, but plain audio), the control channel sounds like it "pulses" from low to high volume very frequently. Something I never observed before, especially in the eastern areas of the county. There's a bit of static on the line, but the overall sound is pretty clear, so whatever the cause of this pulsing it might be why the signal is very weak to my scanner. Just a matter of determining why it's pulsing.
 

mdulrich

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Was already here actually. It says there's both an FCC-registered antenna site and an unregistered cellular tower in the vicinity. I'll have to look around some more for the other antenna, but this first one is hard to miss.
Be sure to look at the antenna listings. You will get a lot more information about who is around than just looking at the towers.

Mike
 

Kumba

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Be sure to look at the antenna listings. You will get a lot more information about who is around than just looking at the towers.

Mike
Good tip, thanks!

Looks like two antennas are defined on the tower I'm seeing. One is broadcasting in the 6./6.1GHz range and another near 10GHz and 23GHz, so I'm not too sure if that means they're somehow interfering with my county's trunked system which operates in the 800MHz range. I figured if they were nearby frequencies, I could get a filter or something to screen out the interference.

Good educated guess, or do I need to do my homework some more?
 

mdulrich

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Not all transmitting sites are on towers. Look for nearby antennas that may be on close frequencies.

Mike
 

Kumba

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Not all transmitting sites are on towers. Look for nearby antennas that may be on close frequencies.

Mike
Yeah, did that too. Two school systems are near by in the ~45MHz range, one private antenna in the 38MHz range, and the antenna carrying the old analog simulcast backup of the county's Fire/EMS system, operating in the ~150MHz range. Closest antenna I can find in the 800MHz block at all is 4mi+ away, and the frequencies it carries look like the future rebanding frequencies that my county is supposed to switch to in time.
 

N0IU

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With all due respect, sometimes you have to do a little more than searching an Internet database to find your answer. I just gotta ask, have you actually been to this tower site? I don't know about your site specifically, but the tower site will most likely have a locked fence around it. In many cases, there will be a sign somewhere on the fence with the name of the owner and maybe even an address or telephone number.

And while I am on an old curmudgeon rant, antennas don't cause interference, transmitters do!

[/rant]OFF
 

Kumba

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With all due respect, sometimes you have to do a little more than searching an Internet database to find your answer. I just gotta ask, have you actually been to this tower site? I don't know about your site specifically, but the tower site will most likely have a locked fence around it. In many cases, there will be a sign somewhere on the fence with the name of the owner and maybe even an address or telephone number.

And while I am on an old curmudgeon rant, antennas don't cause interference, transmitters do!

[/rant]OFF
Been to it - Nope. But I can quite easily see it, since it's literally right across the street from my neighborhood, and it's got a ton of warning lights on it due to the local airport nearby (that services mostly Cessnas and such). I've mostly just pieced together that with both the handheld antenna (Maldol AH-W100RX) and connected to the Larsen tri-band in my car, I get really shoddy signal reception while in the neighborhood. If I drive either left or right on the main road just a few hundred feet (especially left, which puts me out on MD210, a major highway), the signal jumps up quite a bit. Still a touch spotty, but I can hear voice traffic without it being garbled every other word.

This suggests to me that something is creating interference where I'm at, based only on logical deduction without any formal training or a solid understanding of radio (I've learned a few things, but I am no master). I don't know if it's interference from the antennas mounted on this large tower, if it's creating some kind of a void near its vicinity, or if for some unknown, Murphy's Law-like reason, the county's public safety system just doesn't reach this particular neighborhood very well.

I did notice with the control channel (mentioned earlier in the thread), that I don't hear a lot of actual interference hitting the control channel sound. Instead, I hear the volume of the control channel "pulsing". Like the signal keeps coming in weak and then suddenly strong again. I'm not sure if that makes any difference, but that said, Unitrunker's scope on the discriminator definitely doesn't show a clean waveform at all. So something is getting in the way.

All I figured was if this tower had something on it that might be interfering, I could find a way to filter or bypass it, or maybe I just need a better antenna.

PS, and yes, it does have a fence around with with some control shed. It's literally in some guys back yard.
 
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