On 9/14/18 12:11 PM, 'Jeff DePolo' jd0@... [Repeater-Builder] wrote:
I have a question for the Quantar users. When we narrow
banded (Part 90), I had a P25/Astro CAI quantar that would
not receive three or four out of 50 XTL Mobiles (all mobiles
have the same codeplug). When I looked at the programming, I
had set the Receive Channel BW to Narrow 12.5 KHz. Opening
up the bandwidth to Narrow 12.5 -15.0 KHz, solved the
problem.
Sounds to me like the few "bad" mobiles are either off frequency or the
two-point modulation isn't aligned correctly. As far as the latter issue,
if the reference oscillator mod is wrong, it could be over-shooting the low
frequencies, which has a similar effect to the carrier being off frequency,
albeit swinging both high and low.
^ TSRH
The quantar has a different sort of receiver, it's second IF is direct to DSP,
and the demod is done in the DSP chip on the SCM. They are very sensitive to
lack of deviation in p25.
The 900 MHz requires an external reference, so I'm going to assume it's not
the repeater being off frequency.
The other thing is the 12.5-15 KHz setting is normally used at 900 MHz, but
only if you're running "noise canceler" (aka hearclear). For P25 only, 12.5
only is better as you get about 20 dB more adjacent channel performance. If
you don't need this, there's no issue with running 12.5-15 KHz on receive, the
transmit is still 2.5 KHz.
It's likely these XTL's are suffering at the edges of your receiver area too,
you should really identify and check them out.
--
Bryan Fields
727-409-1194 - Voice
