UHF P25 Signal - 13 Miles

nebj00la

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I’ve been trying to pick up a Digital P25 UHF signal (482.5875) from 13 miles away, with interesting results. I started, just to see what would happen, with a UHF/VHF TV antenna. The cable run is about 50ft of RG6 solid core. When the antenna is in the attic, I can get a decent/weak signal when pointing the antenna in the direction of the station. Thinking I’d be able to get a stronger signal, I purchased a discone antenna and some LMR400 cable. The result, I could barely see the signal using SDR. No sync, no audio.

Will I need a special range antenna for this purpose, or should I just stick with the TV antenna? Will it possibly help to raise the discone outside on a mast? I’m trying to avoid that, as I rent the space I’m currently at.

Thanks,
nebj00la
 

natedawg1604

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What part of the country are you in? Unless you're in one of the limited areas where UHF T-band is used, you're probably seeing intermod on 482.
 

nebj00la

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Massachusetts, south coast area. The signal I’m interested in is municipal police, and I’ve successfully listened to a locked on signal with the TV antenna. Just looking to get a stronger signal at this point with an antenna that’s made specifically for UHF 482.
 

natedawg1604

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Massachusetts, south coast area. The signal I’m interested in is municipal police, and I’ve successfully listened to a locked on signal with the TV antenna. Just looking to get a stronger signal at this point with an antenna that’s made specifically for UHF 482.
Oh wow your area does have T-band. So if you're having trouble picking up the site I would seriously consider a yagi antenna cut for UHF T-band (from a good company like Larson or Wilson). I would think 13 miles is pretty darn close, even if it was a low power site. But regardless a yagi is always a good option. Make sure you're getting a yagi specifically designed for Land mobile radio (as opposed to tv).
 

ecps92

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Depending on your actual location and the terrain to where the Repeater is , 13 mi is nothing, a back of set antenna should handle it from a scanners perspective as I am over 35 miles and get them.

IS the antenna a Beam ? and is it pointed in the correct direction ?


I’ve been trying to pick up a Digital P25 UHF signal (482.5875) from 13 miles away, with interesting results. I started, just to see what would happen, with a UHF/VHF TV antenna. The cable run is about 50ft of RG6 solid core. When the antenna is in the attic, I can get a decent/weak signal when pointing the antenna in the direction of the station. Thinking I’d be able to get a stronger signal, I purchased a discone antenna and some LMR400 cable. The result, I could barely see the signal using SDR. No sync, no audio.

Will I need a special range antenna for this purpose, or should I just stick with the TV antenna? Will it possibly help to raise the discone outside on a mast? I’m trying to avoid that, as I rent the space I’m currently at.

Thanks,
nebj00la
 

a417

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I’ve been trying to pick up a Digital P25 UHF signal (482.5875) from 13 miles away, with interesting results. I started, just to see what would happen, with a UHF/VHF TV antenna. The cable run is about 50ft of RG6 solid core. When the antenna is in the attic, I can get a decent/weak signal when pointing the antenna in the direction of the station. Thinking I’d be able to get a stronger signal, I purchased a discone antenna and some LMR400 cable. The result, I could barely see the signal using SDR. No sync, no audio.

Will I need a special range antenna for this purpose, or should I just stick with the TV antenna? Will it possibly help to raise the discone outside on a mast? I’m trying to avoid that, as I rent the space I’m currently at.

Thanks,
nebj00la
your discone is an omnidirectional antenna with essentially zero gain, your TV antenna is directional antenna with some gain. Try what @KevinC said with the LMR on it and see if it improves.
 

popnokick

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You can replace the RG6 if you like with LMR, but it's probably unnecessary. Step One is to rotate the TV antenna on its axis to change it from the "normal" horizontal polarity of most TV antennas to make it have vertical polarization... which is what 99% of public safety / land mobile radio uses. If you left the TV antenna in its normal mounting it's probably horizontal... and you could be losing 20dB or more of signal due to cross-polarization. So turn the antenna on its mount so that the antenna elements point straight up and down (earth - sky) rather than having all the elements parallel to ground. And as you have done already ensure you point the antenna toward the signal source. Once you've done that and determined if there is a signal improvement you can then make an informed decision about whether it's necessary to replace the coaxial cable... a non-trivial task.
 

nebj00la

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Flip the TV antenna 90 degrees and see if that helps (as well as aiming it in the proper direction).
The TV antenna works better than the discone antenna, and that is with the 90 degree flip pointing at the station.
 

nebj00la

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You can replace the RG6 if you like with LMR, but it's probably unnecessary. Step One is to rotate the TV antenna on its axis to change it from the "normal" horizontal polarity of most TV antennas to make it have vertical polarization... which is what 99% of public safety / land mobile radio uses. If you left the TV antenna in its normal mounting it's probably horizontal... and you could be losing 20dB or more of signal due to cross-polarization. So turn the antenna on its mount so that the antenna elements point straight up and down (earth - sky) rather than having all the elements parallel to ground. And as you have done already ensure you point the antenna toward the signal source. Once you've done that and determined if there is a signal improvement you can then make an informed decision about whether it's necessary to replace the coaxial cable... a non-trivial task.
Definitely flipped 90 degrees, otherwise it doesn't get the signal. I've just ordered an adapter for the F-Type connection on the TV antenna to the LMR400 PL259 connection.
 
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nebj00la

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Depending on your actual location and the terrain to where the Repeater is , 13 mi is nothing, a back of set antenna should handle it from a scanners perspective as I am over 35 miles and get them.

IS the antenna a Beam ? and is it pointed in the correct direction ?
The TV antenna that works vertically is Yagi. I believe the cause of the issue is the elevation profile, attached.
Untitled.png
 

popnokick

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If that elevation profile is with your antenna / receiver on one end and the transmitter / source on the other (as is the case with any useful elevation profile), then it is highly unlikely you are receiving the desired signal directly from the source that is transmitting. RF just doesn't make it through huge chunks of dirt and rocks (called "the earth"). So how is the TV yagi able to hear any of it at all? It is very likely picking up a reflected signal(s).... particularly at those frequencies. Pointing your antenna in the compass direction of the signal source (and the side of those mountains) may actually not be where you're going to get your best reception. Have you rotated the antenna 360 degrees (azimuthal rotation) to determine if there is a better signal coming from a reflected source that you might not have realized before? Unfortunately, unless you're picking up a control channel on the system you want to hear with a continuous signal, then your "rotation / find better signal" test is going to have to be done in small increments while each time waiting for another transmission and noting the S-meter or other indication.
 

nebj00la

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If that elevation profile is with your antenna / receiver on one end and the transmitter / source on the other (as is the case with any useful elevation profile), then it is highly unlikely you are receiving the desired signal directly from the source that is transmitting. RF just doesn't make it through huge chunks of dirt and rocks (called "the earth"). So how is the TV yagi able to hear any of it at all? It is very likely picking up a reflected signal(s).... particularly at those frequencies. Pointing your antenna in the compass direction of the signal source (and the side of those mountains) may actually not be where you're going to get your best reception. Have you rotated the antenna 360 degrees (azimuthal rotation) to determine if there is a better signal coming from a reflected source that you might not have realized before? Unfortunately, unless you're picking up a control channel on the system you want to hear with a continuous signal, then your "rotation / find better signal" test is going to have to be done in small increments while each time waiting for another transmission and noting the S-meter or other indication.
Indeed the beginning is rx and the end is the tx. That's a state forest with a nice elevation gain right in the path. I've tried walking around 360 degrees, and the best signal is when I point it essentially in a direct line with the tx station. Now I'm more interested in finding out why that is. Tomorrow the F-Type connector adapter arrives, and I'll be able to see if using LMR400 cable improves the performance substantially over the RG6 cable.
 

popnokick

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Let's look at what you'll gain with the LMR400... and some things that may result in net loss.
On the plus side, the "magic" LMR400 cable that solves every antenna problem here on RR ;-) is only about 1dB less loss than your RG6 at 482 mHz. So less loss is all good, right? Maybe not. Here are the potential losses you'll introduce when switching the RG6 coax from the TV antenna over to LMR400. 1) If you are attaching (crimping or soldering) your own connectors to the LMR400, you run the risk of an open or short in a misapplied connector. If you do LMR400 cables and connectors all the time as part of your job and have the right tools, this is not much of a factor. But if you're not in that category... well, it happens to many of us when attempting to do our own connectors on LMR400. 2) You will be introducing a minor loss with the adapter you're planning to use to go from the F-connector to whatever connector is on your LMR400. 3) TV antennas are 75 ohm devices, and you will experience some loss by using the 50 ohm LMR400 with the TV antenna.
Add all three of the above together and you could possibly come out with a higher loss in the LMR400 cable than you had with the RG6 that is working right now.
Also, I am confused when you wrote, "...I've tried walking around 360 degrees.." in reference to my suggestion to rotate the TV antenna 360 degrees. Do you mean you picked up the antenna and mast and walked around with it looking for a stronger signal? All I wanted you try was to rotate the antenna by either turning the mast / antenna or using the TV antenna rotor (if you have one) to find the best signal... likely coming from a reflected source. Once you've done that THEN if you want to move the antenna left / right / up / down so as to have a better line of sight to the mountain or building that is providing the signal you can do so.
 

nebj00la

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Let's look at what you'll gain with the LMR400... and some things that may result in net loss.
On the plus side, the "magic" LMR400 cable that solves every antenna problem here on RR ;-) is only about 1dB less loss than your RG6 at 482 mHz. So less loss is all good, right? Maybe not. Here are the potential losses you'll introduce when switching the RG6 coax from the TV antenna over to LMR400. 1) If you are attaching (crimping or soldering) your own connectors to the LMR400, you run the risk of an open or short in a misapplied connector. If you do LMR400 cables and connectors all the time as part of your job and have the right tools, this is not much of a factor. But if you're not in that category... well, it happens to many of us when attempting to do our own connectors on LMR400. 2) You will be introducing a minor loss with the adapter you're planning to use to go from the F-connector to whatever connector is on your LMR400. 3) TV antennas are 75 ohm devices, and you will experience some loss by using the 50 ohm LMR400 with the TV antenna.
Add all three of the above together and you could possibly come out with a higher loss in the LMR400 cable than you had with the RG6 that is working right now.
Also, I am confused when you wrote, "...I've tried walking around 360 degrees.." in reference to my suggestion to rotate the TV antenna 360 degrees. Do you mean you picked up the antenna and mast and walked around with it looking for a stronger signal? All I wanted you try was to rotate the antenna by either turning the mast / antenna or using the TV antenna rotor (if you have one) to find the best signal... likely coming from a reflected source. Once you've done that THEN if you want to move the antenna left / right / up / down so as to have a better line of sight to the mountain or building that is providing the signal you can do so.
Neither antenna has been permanently mounted yet, as this just started as an experiment when I discovered the P25 signal. This was unexpected. By 360, I meant, I've walked around the highest levels of my building pointing various directions while waiting for the station to transmit. The only way I'm able to rx is by pointing in the general direction of the tx station, as seen on both my SDS100 and SDR.

I ordered a 50ft LMR400 cable with connectors when I started the testing, as I didn't think the "old TV cable I found in the basement of the house I rent" would make the cut. Funny how that worked out.
 

StoliRaz

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Did you bother to get a yagi or better antenna? Just wondering. I don't live far from you and can only seldom get NBPD. Think I have the same issue except that I'm even father away than you are.

Looking north, same issues with Moose Hill and the Blue Hills. Damned terrain
 

merlin

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I will back up and push a bit here. Your TV antenna mounted vertically should give improvement.
50' coax run, nothing wrong with the RG6. Elevation is your friend, the higher you can get your antenna, the better.
If terrain is a problem, you may be getting refection from another direction, swing the antenna for maximum signal.
About your discone. You sacrifice gain for being omni directional as well as broadband. you need amplification, probably 20Db of it. For single band, a UHF Yagi would work better directionally.
Your SDR. They are not designed with radio in mind, the front end is a TV tuner. You need 0 to +10 Dbm for them to work well. they have no filtering for any specific band. for you, a UHF bandpass filter would help a lot. No heavy AGC issues and noise interference.
My discone is 6' atop a 2 story flat roof. LMR400 55' run. first stop is an FM BC trap into 15Db gain drop amp.
Inside, a bandpass filter and another 21 Db gain amp then into the SDR.
State police dispatch is 9 miles, flat terrain and I just do get a decent signal. the repeaters are 22 and over miles on surrounding mountains, one too weak to be useable. Bad enough I am in an RF dead zone with a major repeater and cell site next door. Hope I have enlightened you a bit with this.
73s
 
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