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Combat simulcast distortion on P25 conventional system?

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#1
I am monitoring the testing phase of my county's new VHF P25 phase 1 conventional radio system and am experiencing some simulcast distortion just as I would on a P25 trunked radio system. I should add that I am recording during the day while I am at work using my Homepatrol (HP-1) using an Antennacraft ST-3 mounted in my attic.

I know that, with a P25 trunked system, you can just program the closest site to your location and that helps. What is the answer with a P25 conventional system? Being as a conventional system has no sites programmed, it would seem that the only way to combat it would be LESS antenna sensitivity so that it would only pick up the closest tower? I was thinking about trying it using just the original antenna that came with the HP-1.

Is there another way I am missing...other than using a directional antenna like a yagi?
 
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2,542
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#2
Monitoring your P25 system

Your post is some what confusing with the description your providing. You mention it is a VHF P25, phase 1 system. Then you call it a conventional system. Lastly you make the comment that it has simulcast distortion.

If it is a simulcast system, then each tower and each control channel and each voice channel will all be the same at all locations. Is this the case with the system your trying to monitor? If there are different control channels active at the different towers, then it can't be a simulcast system.

You need to provide this information before anyone can even make a guess as to how to start to resolve what your calling distorted reception.

Providing some information like the control channel and voice channels might allow doing a search for the license and that will provide some additional details as to how the radio system is functioning. Where the system is located is also needed to help build on the details of the system.
 

wa8pyr

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4,244
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Ohio
#3
I am monitoring the testing phase of my county's new VHF P25 phase 1 conventional radio system and am experiencing some simulcast distortion just as I would on a P25 trunked radio system. I should add that I am recording during the day while I am at work using my Homepatrol (HP-1) using an Antennacraft ST-3 mounted in my attic.

I know that, with a P25 trunked system, you can just program the closest site to your location and that helps. What is the answer with a P25 conventional system? Being as a conventional system has no sites programmed, it would seem that the only way to combat it would be LESS antenna sensitivity so that it would only pick up the closest tower? I was thinking about trying it using just the original antenna that came with the HP-1.

Is there another way I am missing...other than using a directional antenna like a yagi?
The solution is the same as it would be with a P25 trunked simulcast system; you have to work out a way to ensure that you're receiving from only one tower at a time. That can be with a directional antenna, or less antenna, or use of the attenuator, or various combinations of those.
 
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Newport, PA
#4
Your post is some what confusing with the description your providing. You mention it is a VHF P25, phase 1 system. Then you call it a conventional system. Lastly you make the comment that it has simulcast distortion.

If it is a simulcast system, then each tower and each control channel and each voice channel will all be the same at all locations. Is this the case with the system your trying to monitor? If there are different control channels active at the different towers, then it can't be a simulcast system.

You need to provide this information before anyone can even make a guess as to how to start to resolve what your calling distorted reception.

Providing some information like the control channel and voice channels might allow doing a search for the license and that will provide some additional details as to how the radio system is functioning. Where the system is located is also needed to help build on the details of the system.
I called it a P25 conventional system because it is not a trunked system. As far as calling it distorted reception...I am familiar with simulcast distortion from the one trunked P25 system that I monitor. The person is talking, the signal is strong and then it either drops off or becomes garbled.

I am not into amateur radio, so I do not have a vast amount of knowledge on how radio systems are constructed. I am going by my 35+ years of scanning knowledge (mostly analog). I know that this is a 10 frequency VHF system on a P25 platform and will be simulcast. It is definitely not trunked.

This is a link to the system on the FCC website. Note that it was ORIGINALLY planned as a trunked system, but was later modified to conventional.
ULS Application - Public Safety Pool, Conventional - 0007129798 - PERRY, COUNTY OF
 
Joined
Mar 6, 2005
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Location
Gilcrest, CO
#5
I called it a P25 conventional system because it is not a trunked system. As far as calling it distorted reception...I am familiar with simulcast distortion from the one trunked P25 system that I monitor. The person is talking, the signal is strong and then it either drops off or becomes garbled.

I am not into amateur radio, so I do not have a vast amount of knowledge on how radio systems are constructed. I am going by my 35+ years of scanning knowledge (mostly analog). I know that this is a 10 frequency VHF system on a P25 platform and will be simulcast. It is definitely not trunked.

This is a link to the system on the FCC website. Note that it was ORIGINALLY planned as a trunked system, but was later modified to conventional.
ULS Application - Public Safety Pool, Conventional - 0007129798 - PERRY, COUNTY OF
Non-trunked stand-alone digital P25 stations will experience decoding issues when the signal strength being received is low. I'm not sure if you are monitoring transmissions from a repeater (radio tower) or directly from moving sources such as vehicles? In either case, better reception is required which may be as simple as relocating the receiver or may require that a better antenna be purchased or that an existing antenna be mounted at a higher elevation to obtain better reception of faint signals.
 

ofd8001

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Feb 6, 2004
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Louisville, KY
#6
Sometimes setting attenuation can be helpful. Also tinkering with the P25 settings (Threshold levels, etc.) can be helpful, though I don't know how on this model as I don't have one.
 
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