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Avoiding a trunk system frequency. Possible?

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sshermanmd

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#1
I like to monitor some of the San Bernardino trunk sites with an 800 MHz yagi I have here in SE Los Angeles county. These sites are 50 to 60 miles or more away, but I have no real problem getting the control channel (CC) on several sites. The problem is the voice channels (VCs). I live in Radio Jungle Los Angeles and Orange County and Riverside County are in between, so there is 800 MHz activity up the wazoo.
The SBDO trunking system (TRS) is a Motorola II Smart Zone system, so the CC is obviously assigning the VCs. However, a few of the VCs are near other CCs or VCs of other systems, so when a particular talk group (TG) gets assigned to that VC, I hear a lot of buzzing, QRM, and crud. Locking out the TG is no good, because the next go around, that TG is likely to be assigned to another VC. So my question is can someone lock out a VC on a TRS.
I deleted the offending VCs in their respective trunk sites, but that means only that my scanner (536HP in this case) won't look at that frequency as a possible CC. But that does not prevent the SBDO TRS from assigning that VC, to which my scanner then automatically goes to (same principle as when using Unitrunker to control scanner.)
One can obviously lock out a frequency on a conventional system, and one can lock out TGs on a TRS. But is it possible to lock out a VC on a TRS such a scanner won't go to that frequency when the TRS assigns any TG to that VC frequency.
Any suggestions appreciated.
 

troymail

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Supply (Lockwood Inlet area), NC
#2
As you said - the VC assignments are made as a result of what is sent on the CC frequency so I don't think you can "skip" selected VC frequencies.

You could program each system frequency as conventional (and leave out the bad frequency) but there are certain to be other issues going this route.
 
Joined
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Clinton County, MO
#3
I had a similar problem.

I have a site on Missouri's statewide system 30 miles north of me that uses 154.905 as a voice channel.
Another site 80 miles south uses that same frequency as a control channel.

The voice channel wins the challenge, however after the transmission, the scanner never resumes scanning because it thinks the control channel data it's hearing is more voice data.

I 'worked-around' the problem by creating a custom table that omitted instructions for calculating that particular frequency.
Because the scanner now lacks information to map a channel number to a frequency, it continues to scan as if nothing happened.

Another option is to map the problem channel to the mobile input frequency. In this scenario there is still a chance of catching the transmission if the mobile is in range.

This works on my GRE, but I am told that the Uniden radios ignore custom band plans when the band plan is broadcast over the P25 control channel.

As far as Smartnet/Smartzone go.......there might be a chance you can manipulate the band plan.
 
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ofd8001

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Louisville, KY
#6
Have you tried setting Site Attenuation on for both the desired and "infecting" systems? It may not help, but would be worth a try.

Also if you change Squelch settings to something more "tight" does that help?

Probably at the end of the day it's a selectivity issue and your scanner may be more "forgiving" for adjacent frequencies thus you get the ingress.
 
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