Tower broadcast range.

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BudworthTDog

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I am pretty new to the game. I live in a populated area (Columbus, Ohio) and want to monitor the police departments P25 system. Since it's such a populated area and the airwaves are congested I figured a directional antenna would be a good idea. The system I want to monitor simulcasts from 6 towers around the area. One is listed as a broadcast strength of 75 (I'm assuming watts) and the other 5 are listed as 150 watts.

My question is about how far will those towers broadcast? The stations are in the 850MHz range and it's pretty flat here so for the most part terrain shouldn't matter. I'm confident that at least one of them will be within range, the closest one is just under 6 miles as the crow flys. My main concern is with it being such a populated area that interference may factor into which tower to aim it towards. Basically, the closest tower may not be the best tower. I was wondering with towers broadcasting at that strength at what distance should I consider a tower not eligible as a canidate? The antenna I have is the TerraWave 806-960 MHz 10dBi Enclosed Yagi Antenna.

Thanks,
Nathan
 

W8RMH

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The problem with the Columbus MARCS system is Simulcast / Multi-path Distortion. If you can give your general location it would help. Try to aim your antenna where it doesn't aim toward more than one tower.

The city system is designed to work within the city limits. The towers are directional as well. Due to the system's design and the simulcast issues you can be less than a mile away and not receive a tower, so range and power is irrelevant. It depends on your location.

I am in Grove City and I aim SE toward the Parsons tower (Scioto Downs), about 7 miles away. There are no other towers in that direction. If I were to aim to the NNE toward downtown it would also be in the direction of the Morse Rd tower and I would experience the multi-path distortion. There is a site in Grove City but it is mostly Grove City and Franklin County traffic.

There are some threads in the Ohio Forum already discussing this system with a lot more information available from those actually listening to this system, not someone 1000 miles away with no clue.

http://forums.radioreference.com/ohio-radio-discussion-forum/335829-columbus-switch-over-marcs-ip.html

http://forums.radioreference.com/ohio-radio-discussion-forum/175238-marcs-ip-new-marcs-site-talkgroup-discussion.html
 
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teufler

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Doing some range calculations with a Motorola Range calculator, and say the towers are 100 ft tall with a 6dbd gain antenna, range estimated at 20.5 miles on the 75 and 23 on the 100. As w8rmh suggested, try ti isolate 1 antenna, to avoid multicast. You can do it two ways, with your beam, aiming at one tower, with no other antennas in you beam pattern, or less is better, going with just enough antenna to receive one tower.Say the closest towers are 5 miles from you, probably no antenna on the scanner would work. You would receive the tower that is withing 5 miles and you could not hear those at 8 to 10 or more miles away. The beams worked great on vhf and uhf but not a big deal on the 800 trunking unless you are say 20 miles from a tower
 

BudworthTDog

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The problem with the Columbus MARCS system is Simulcast / Multi-path Distortion. If you can give your general location it would help. Try to aim your antenna where it doesn't aim toward more than one tower.
Those links are helpful, thanks. I am near Sullivant/Norton on the far westside. I had my antenna pointed at the Dublin Rd tower. I saw some reports of the 859.2125 control channel having degraded signal durring certain times/conditions, especially on the westside. I think I may have seen this the other day but contributed it to the fact that I had switched from the RTL-SDR dongel to the Airspy. Which I thought was weird since the Airspy is better hardware. I didn't really have time to troubleshoot it at the time so I dont want to chime in saying that I experienced the trouble until I know it's not with my new set up.

I'm sure I will have to deal with things/issues that aren't typical on here since most people are using scanners instead of SDRs. They are a better choice for me since I want the option of flexibility though. I'm a technician with Spectrum (TWC) and just want to learn more about the world of RF. We will see how things play out
 
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