P25 Question about RSSI

[scannerowner]

This is kinda in response with the MO Discussion, MOSWIN, but I don't know the specifics on a P25 trunked system.The radio tech's radio shows a RSSI of 58 on a Site that is only 10 miles away from him using a Mobile Radio and he says it should be atleast double that, if this is true, how do you improve the RSSI on a single site. For those that don't know, MOSWIN is a 71 Site VHF P25 Trunked System in MO. To fix the problem do they have to move the antenna off the tower to another location, or what other options do they have to fix it? I wish I knew more about P25 radio systems and the technical side of how they work. This is not a scanner question.

 

[WA0CBW]

The simple answer is fix what is broken. It could be that the transmitter(s) aren't putting out full power or there is a problem with the coax, connectors, antenna, etc. It could even be the terrain (such as a hill or valley) that is causing the problem. If everything is working the only way of increasing the ERP of the site is to raise the antenna, increase the transmitter power, decrease the duplexer/transmission line loss, increase the antenna gain, or move the transmitter and the receiver closer to each other

BB.

 

[scannerowner]

Hmm ok, that all makes sense. Guess it just takes time to figure out what is broken and get it fixed then. If it is terrain, what can be done to fix it?

 

[UPMan]

Improve antenna height or bulldoze.

 

[scannerowner]

Don't think it can be bulldozed, but may be able to improve the height, it is at 91.4m, I believe, structure at 96.9m. Elevation is 300.9 m! Now I wonder why it's soo hard to reach ten miles away! The next closest site has an antenna at 328.1m, does almost 90 feet difference make such a BIG difference?

 

[mikewazowski]

Without knowing the specifics of the equipment at the site, there's really no way to tell.

Could be engineered poorly, could be bad equipment, could be mistuned equipment, could be the wrong equipment installed, could even be the test equipment used.

There are many factors which affect a site's RF performance and without more details, we're all just guessing.

 

[WA0CBW]

If it is terrain there isn't much you can do. The obvious solution is to move the site. In reality that is usually not possible. Moving a site and re-coordinating it with the FCC may not be possible due to previous frequency coordination of existing frequencies. When designing systems it usually isn't possible to put the tower where you want it to provide the best coverage. This is due to zoning laws, NEPA requirements, and local coordination limitations. That is why there are always "dead spots" in any system design.

BB

 

[scannerowner]

Thanks all for your responses! I bet they have addressed the problem now and will look into fixing it anyway they can to ensure the safety of those using it! I just hope it doesn't take long before they do!

 

[UPMan]

There is a quick and dirty line-of-sight map web site. See this post for details: http://forums.radioreference.com/general-scanning-forum/115818-how-far-can-i-receive.html

It does not take into account intervening buildings or foliage, but does a good job of indicating line-of-sight coverage based on hard terrain.

 

[scannerowner]

I guess using that at an approximate Elevation shows the line of sight is slightly under what I should have, so technically I should have great reception of it. There are trees and all between the site and where I'm located, but then again the site is only 10.5 driving miles away, 9 miles line of sight, and IS VHF. That's what we are puzzled about. Still makes me think something is wrong with the transmitter because most of the other sites don't report any RSSI issues from wherever they're at, and some are located within the Ozarks of MO. For those that don't know, the Ozarks are the closest thing to mountains around here!

 

[greenthumb]

It really could be anything at all - bad or incorrect antenna, bad or improperly installed connector(s), bad PolyPhaser, bad or mis-tuned cavity filter(s), bad or mis-tuned pre-selector or bad PA in the station. Without taking test gear out to the site and going through everything, there's really no way to tell.

It could even be something wrong with the technician's mobile radio, connector, coaxial cable, NMO mount or antenna too.

 

[AirScan1]

P25 is not perfect yet

 

[PJH]

P25 is not perfect yet

It has nothing to do with P25. RF is RF in general terms.

I'd go more with a problem with the radio being used by the "tech" reading 58. My guess someone is just pressing the RSSI button on the radio and getting a number. Radio could use an alignment, just in a shadow of the site, poor install of the antenna, high RF area.

My guess is the site is fine. Any compentent tech would be at the site and getting pretty good readings to determine any faults between the radio and the antenna.

Some of you are way out in left field.

 

[scannerowner]

Does it matter if I'm 10.5 miles away from the site and on my scanner I get very little reception. Also the actual radio affiliates with a site that is maybe 1.5 or 2 times that distance from the same location. It's very puzzling why it would affiliate with a tower that is twice the distance.

 

[PJH]

You haven't told us how you are coming into this information. Hard to answer the question without knowing hat troubleshoot (if any is needed) has been done and with what equipment.

 

[scannerowner]

Just gathering the information from various sources and after a post in the discussion I was following. I have two sources that use the system and report to me their findings.

 

[PJH]

So basically your guessing and assuming.

Tower affiliation also isn't too big of a deal depending on the talkgroup/system allocation.

I have radios that will affiliate to sites further away that geographically located. I can also get intelligible audio with rssi values as low as 33.

 

[scannerowner]

The system is set up to adjust to which site has the strongest signal. All sites are at the same power level. I think it's a P25 SmartZone setup if I remember correctly.

 

[PJH]

The system is setup that way or the subscribers?

All sites are not setup at the same power level. That's determined by the FCC with the haat.

 

[scannerowner]

The particular site that is having issues is at 100 watts that is VHF and the nearest 800mhz site is pushing 35 watts. I'm receiving the 800mhz site better than the VHF, something is odd there!