Quantar VHF P25 RX issue

[WX5812]

I have a VHF Quantar that's been working fine till lately. My issue is that it will RX fine in analog. a good 50+ mile coverage. P25 coverage in RX is about half of that. I'm not sure what's going on with it. I have checked SWR and even read and rewrote the codeplug. Before hand P25 was able to RX beyond the 50ish mile coverage. Has anyone seen similar behavior before?

 

[prcguy]

Have you checked the digital alignment of any transmitters talking to it? I just picked up a VHF Quantar and a bunch of spare parts south of Dallas but shipped them to So Cal, otherwise I would loan you a receiver to try out.

QUOTE="WX5812, post: 3618982, member: 1191040"]
I have a VHF Quantar that's been working fine till lately. My issue is that it will RX fine in analog. a good 50+ mile coverage. P25 coverage in RX is about half of that. I'm not sure what's going on with it. I have checked SWR and even read and rewrote the codeplug. Before hand P25 was able to RX beyond the 50ish mile coverage. Has anyone seen similar behavior before?
[/QUOTE]

 

[jeepsandradios]

I'd get it on a service monitor and look at the receiver. RX Alignment sounds like the place to start.

 

[WX5812]

Have you checked the digital alignment of any transmitters talking to it? I just picked up a VHF Quantar and a bunch of spare parts south of Dallas but shipped them to So Cal, otherwise I would loan you a receiver to try out.

QUOTE="WX5812, post: 3618982, member: 1191040"]
I have a VHF Quantar that's been working fine till lately. My issue is that it will RX fine in analog. a good 50+ mile coverage. P25 coverage in RX is about half of that. I'm not sure what's going on with it. I have checked SWR and even read and rewrote the codeplug. Before hand P25 was able to RX beyond the 50ish mile coverage. Has anyone seen similar behavior before?

[/QUOTE]
I forgot to add that I have used 6 different radios to test it out. XTL2500,APX7500/8500, APX7000, and 8000 with the same result.

 

[WX5812]

I'd get it on a service monitor and look at the receiver. RX Alignment sounds like the place to start.

Yes, I will do that for sure but what gets me is the analog out performs the p25.
An alignment will fix it hopefully. preselector may be way off.

 

[prcguy]

RF alignment as in the front end should have the same degradation on P25 as it does on FM analog. If there are any other alignments on the receiver besides the screws sticking out the front I'm not familiar with it but you might check the VCO voltage to see if its on the edge. I've seen other types of equipment where the VCO was about to go out of lock and the phase noise went sky high affecting digital mod and demod.

Is this a R2 VHF being used on the lower end of 2m by any chance? The only P25 I see in your area is the 146.86 in Arlington.

Yes, I will do that for sure but what gets me is the analog out performs the p25.
An alignment will fix it hopefully. preselector may be way off.

 

[WX5812]

RF alignment as in the front end should have the same degradation on P25 as it does on FM analog. If there are any other alignments on the receiver besides the screws sticking out the front I'm not familiar with it but you might check the VCO voltage to see if its on the edge. I've seen other types of equipment where the VCO was about to go out of lock and the phase noise went sky high affecting digital mod and demod.

Is this a R2 VHF being used on the lower end of 2m by any chance? The only P25 I see in your area is the 146.86 in Arlington.

This is an R2 but its on the 151/156 range. Its been fine for years. The only thing that changed was the heat went out at the site a while back (its back now).
Im with you on the degradation. It should be the same if not better coverage on p25. Instead its the opposite plus some.

 

[prcguy]

I have a manual and if I get time I'll look up the receiver alignment to see if there is anything besides the front panel screws.

This is an R2 but its on the 151/156 range. Its been fine for years. The only thing that changed was the heat went out at the site a while back (its back now).
Im with you on the degradation. It should be the same if not better coverage on p25. Instead its the opposite plus some.

 

[jeepsandradios]

I would check BER on the receiver first to make sure its at 5% around -119dBm. If you have high BER that would cause loss of coverage. I don't see a lot in the manual for Digital Optimization other than "tune preselector"

 

[MTS2000des]

What's the noise floor at the site? Lots of "hash and trash" can cause high BER but analog FM still "usable". Start with a site baseline, but I'm in full concurrence, a full alignment on a Quantar would not hurt. Remember these are getting up there in age. Probably time for a full work up if it hasn't been done in the last 12-18 months.

 

[prcguy]

Good test to run but you would need a service monitor with P25, not common outside of a public service radio shop.

I would check BER on the receiver first to make sure its at 5% around -119dBm. If you have high BER that would cause loss of coverage. I don't see a lot in the manual for Digital Optimization other than "tune preselector"

 

[N4DES]

I would also do an ISO "T" test to see if there is any noise degradation through your duplexers that your ear might not hear....

 

[WX5812]

I did not have my 8800 with me when I went out there the other day. I plan on trying to make it out there tomorrow with it to dig in-depth. I did notice last time I was out there that there was some noise on my HT that normally wasn't there. Like MTS2000des said, that could be some of the issue. Will also recheck the duplexer as well.