P25 Signal Split

[devicelab]

FYI, if you don't use a SDR then this thread probably won't make any sense.

Has anyone noticed how some P25 signals (that are fairly strong) have a split in the signal transmission? I've noticed when this happens I cannot decode them on DSD+ or any other application (like Unitrunker, etc.)

I'm just curious if anyone has tracked down to the reasons for this split. Another observation: a site that came in S9 before is still S9 but the signal has show this split -- and now, I can no longer decode it.

At first I thought this was just distance related and thus a SNR problem. Now I'm not so sure. FWIW, I've seen this across the spectrum so I don't believe it's a frequency thing.

From the picture below, I cannot decode the red circle, but I can decode the two control channels on the right.

 

[tweiss3]

Is either simulcast?

 

[devicelab]

Is either simulcast?

The sites above are not --- but I've had an issue with another in the 85x range and it is simulcast.

 

[AM909]

If you used the narrowest sampling (maybe 250 kHz), is it different? Can you zoom in some more? Looks like two different carriers of different strengths spaced about 2.5 kHz apart but more resolution would be good. I assume this is supposed to be one of the mil P25 systems? Maybe it's a test signal. I remember something about Bessel nulls, but I must have been asleep during that year in school.

 

[devicelab]

If you used the narrowest sampling (maybe 250 kHz), is it different? Can you zoom in some more? Looks like two different carriers of different strengths spaced about 2.5 kHz apart but more resolution would be good. I assume this is supposed to be one of the mil P25 systems? Maybe it's a test signal. I remember something about Bessel nulls, but I must have been asleep during that year in school.

Yes, I can narrow in quite a bit. No it's not a test signal. These are working P25 control channels.

FWIW, I think this is multipath. This happens a lot around here.