Problems Receiving Control Channel.

[Safe30]

I want to listen to a Motorola Project 25 Phase 1, 800 Mhz. System that uses APCO-25 Common Air Interface Exclusive Voice. The system has 8 Simulcast Sites. 98% of my listening would be within the simulcast area.

The scanner is a Uniden BCD 396XT Trunk Tracker IV. Only the Control Channel Frequencies are programmed into the scanner.

The scanner is turned on and begins searching for the control channel. The channel is found and the signal strength indicator begins to rise. After about 1 ½ minutes the signal strength indicator shows full strength. The signal remains at this level for about 2 minutes and then begins dropping. About 1 ½ minutes later the scanner has lost the control channel and after some seconds the cycle starts again with the scanner looking for the control channel.

During the time the scanner is receiving the control channel at mid level or above it seems to operate satisfactorily. Other times I’m missing calls. Scanner location has no effect at all on the cycling. ATT (enuation) eliminates reception of the control channel completely. Close call, priority and weather priority are off.

Is there any way of knowing if a 325P2 or 436HP would have the same problem?

Thoughts, ideas, solutions(?) please?

Safe30.

 

[WA0CBW]

If using the attenuator eliminates reception of the control channel it may mean you are not getting a very strong signal from the system. It could be that your are not close enough to the system. Are you using the supplied antenna or do you have an outdoor antenna?
BB

 

[W8RMH]

Simulcast digital distortion - The RadioReference Wiki

 

[ofd8001]

The fluctuating signal strength indicator for the control channel isn't an issue. Upman once said this is due to "internal housekeeping" of the scanner.

I've monitored several different simulcast systems with the 396XT and it can be challenging.

The main issue is the scanner is receiving multiple sites and is having trouble decoding the multiple signals into something understandable. Unfortunately this often means either no audio or garbled audio.

Some things to try (I've seen some improvement, but not stellar):

Site Attenuation On
Tweaking P25 Adjust Mode
Tweaking P25 Adjust Level

(There is no one size fitting all on the P25 settings. You have to find your sweet spot with trial and error. It does take patience).

I can't speak about the 325 or 436 models, however my two 536's are a whole lot better with digital simulcast systems than my 396XT. If I understand correctly, the Phase II version scanners use a different Vocoder than the x96 scanner series.

I'm at the point where I only use my 396XT if I don't have access to the 536s.

 

[Voyager]

The fluctuating signal strength indicator for the control channel isn't an issue. Upman once said this is due to "internal housekeeping" of the scanner.

Depends how you define "fluctuating".

It is normal for the S-meter to drop every couple seconds and come back again. That is what UPMan was talking about. Faster fluctuations (or slower ones) could be simulcast interference which is something completely different.

 

[Safe30]

Thanks for responses.

Thanks for the responses to my problems receiving a control channel on my BCD 396XT. As a result of the responses I’ve changed my mind about the situation. It now seems like I’m the victim of the dreaded Simulcast Breakup.

Some comments and a little babbling:
If the signal strength indicator on the 396 isn’t an issue, it means the scanner is either hearing the channel or not. No up and down strength. Therefore Breakup.
I was originally listening with the stock antenna. In the last couple of days I put a Diamond RH77CA on the scanner and tried it at my usual locations. No change. The scanner needs to remain a handheld so a directional antenna isn’t practical.
Location isn’t a factor. The problem exists at locations ranging from ¾ of a mile to a site, with no obstructions between (not even a pane of glass), to my deep dark basement about 4 ¼ miles to the closest site.
I’ve been working with the P25 Adjust settings for a little while but no joy yet.

So, now I think I need to consider if something newer would be more effective. I’ll start reading posts again.

Again, thanks for the ideas.

Safe30

 

[ka3aaa]

Put an outdoor antenna up and lock out all the control channels out but the strongest one and you should be fine.

 

[Voyager]

Put an outdoor antenna up and lock out all the control channels out but the strongest one and you should be fine.

It is not possible to lock out all but one control channel in a simulcast system since they are all on the same frequency.

 

[W8RMH]

Put an outdoor antenna up and lock out all the control channels out but the strongest one and you should be fine.

Uhhh...that won't work. You need to read up on Simulcast Digital Distortion.