Somerset Site 4 700 MHZ

[rr60]

Heads up Somerset County Site 4 listeners.

Site 4 700MHZ has had a good run using 774.40625 as the primary CC for many years. That may be coming to an end this spring as the tropo season begins.

Salem County is rolling out its new system and is presently using the same frequency as Somerset for its primary CC.

Dozens of times a year 700 MHZ systems from South Jersey (and further) propagate into Somerset. As a result, if these systems stay configured as they are, I expect the CC to start rolling to alternate frequencies.

You may want to check that you have the alternates in your equipment.

 

[FT752]

That's not such a bad thing. Gives the other control channels a chance to get their rotation and release some strain on 774.40625. Now if the licensure mirrored Somerset almost all the way, then it's a big problem. It's 3 extra frequencies; this isn't a Harris system like Middlesex where you have to account for 16+ control channel options.

 

[DBR_M12]

Heads up Somerset County Site 4 listeners.

Site 4 700MHZ has had a good run using 774.40625 as the primary CC for many years. That may be coming to an end this spring as the tropo season begins.

Salem County is rolling out its new system and is presently using the same frequency as Somerset for its primary CC.

Dozens of times a year 700 MHZ systems from South Jersey (and further) propagate into Somerset. As a result, if these systems stay configured as they are, I expect the CC to start rolling to alternate frequencies.

You may want to check that you have the alternates in your equipment.

That would take manual intervention, no? The tropo on site 3 is on the input side also so the system would see it, right?

 

[rr60]

I believe the site controller (or zone controller) continuously monitors the health and performance of the primary control channel, no manual intervention needed unless it was set up differently. It monitors several parameters and even logs and reports.

When it detects degradation or failure beyond acceptable thresholds, it can automatically switched to an alternate control channel if setup to do so.

 

[GTR8000]

Let's be clear about this...the system is only monitoring the input frequencies (799-805), not the output frequencies (769-775).

If 774.40625 were blasting into Somerset from Salem or anywhere else due to propagation, the system would have zero awareness of such, and therefore would not roll control channels based on that condition. Something would have to be hosing up the input in order for the system to roll control channels based on real or perceived interference.

T-Band is a different animal, because the propagation is from DTV stations that occupy the full 6 MHz of bandwidth per block, which includes the repeater inputs for LMR systems. So it's not the fact that the outputs are getting clogged up due to propagation, but the fact that the inputs are as well, which the systems are actively monitoring.

 

[rr60]

Interesting, so then by the luck of the draw Salem picked the same frequency as Somerset. I guess nobody plugged into an antenna and took a look. There would be no reason to have significant activity on the input of a control channel, so the two transmitters will just beat together when the band opens. Hmmm.

The southernmost Somerset site has pretty good coverage south.

 

[GTR8000]

Is this an actual issue, or just the assumption/perception that there will be an issue?

Keep in mind that 700/800 MHz frequencies aren't chosen at random, rather they are strictly coordinated by the Regional Planning Committees (RPC's). In this case, Somerset is covered by Region 8, Salem by Region 28. Frequency applications are first submitted to the RPC before anything sees the day of light as far as FCC licensing. The application is thoroughly reviewed by the home RPC first, then sent to all neighboring RPC's for coordination. If Region 8 and 28 thought this would be a big issue, they would've have signed off before allowing the stations and frequencies to be licensed.

Also keep in mind that all of these systems are using simulcast cells, which do a pretty good job at saturating the intended coverage area with a strong signal. That alone would drown out 98% of any co-channel propagation from another system many miles away. The subscribers will also do a good job at rejecting co-channel interference that doesn't have a matching NAC.

Oh and as for the selection of 774.40625 as the most preferred control channel for each system, that's just coincidence. Generally speaking, the highest licensed frequency is used as the control channel on 700 MHz systems, and guess which frequency happens to be the highest licensed in each county?

 

[rr60]

Presumption. Great intel, thanks for scratching that itch! We shall see what if anything develops.

 

[GTR8000]

I just want to be clear in saying that I'm not suggesting that co-channel interference can't and doesn't happen, it certainly can and does, especially during periods of enhanced propagation. Hell, even adjacent channel interference can pop up from time to time. The issue on 700/800 is much less troublesome as it would be on T-Band due to the "whole chunk of 6 MHz" issue prevalent with the latter that wipes out the inputs, which is just downright nasty.

On a somewhat related note, one smart thing that was done ages ago was to group the 700 and 800 MHz inputs together @ 799-815 MHz (+30 for 700, -45 for 800). This ensures that none of the high power repeaters are right up against the low power inputs of the other band. Perhaps not entirely necessary, but good practice nonetheless. It also allows for easier band pass filtering when you only have to worry about allowing 16 MHz worth of contiguous spectrum to pass through to the receivers.

 

[DBR_M12]

Let's be clear about this...the system is only monitoring the input frequencies (799-805), not the output frequencies (769-775).

If 774.40625 were blasting into Somerset from Salem or anywhere else due to propagation, the system would have zero awareness of such, and therefore would not roll control channels based on that condition. Something would have to be hosing up the input in order for the system to roll control channels based on real or perceived interference.

T-Band is a different animal, because the propagation is from DTV stations that occupy the full 6 MHz of bandwidth per block, which includes the repeater inputs for LMR systems. So it's not the fact that the outputs are getting clogged up due to propagation, but the fact that the inputs are as well, which the systems are actively monitoring.

Thanks for clearing that up and getting the right info out there.