BCD396T Not Decoding P25 for LAPD Valley TAC 1 - CH 42 - 507.0125 MHz

[hotdjdave]

For some reason, my BCD396T is not correctly decoding LAPD Valley Bureau TAC 1 - CH 42 - 507.0125 MHz. It decodes some of the transmissions, but not most of them. When it doesn't decode, I can hear the data/static of the transmission (like a scanner that doesn't have P25 decode), but it doesn't decode.

I don' t seem to have a problem with any other LAPD P25 transmissions.

I have the latest firmware (V1_11_03). My P25 setting for this system (LAPD) is: "7 AUTO." This setting has been working so-so since the firmware update. This problem has been happening since the firmware update. This occurs using both the OEM antenna and an antenna on the roof of my house.

I thought it might be that this channel is used in simplex mode sometimes; but I don't know why that should matter, a P25 transmission should be the same whether or not it is in simplex or semi-duplex (repeater). Could the distance and power of the radio trying to be received effect the BDC396T's ability to decode P25?

 

[mancow]

Try different decode settings. I think it makes more of a difference than people realize.

 

[kikito]

For some reason, my BCD396T is not correctly decoding LAPD Valley Bureau TAC 1 - CH 42 - 507.0125 MHz. It decodes some of the transmissions, but not most of them. When it doesn't decode, I can hear the data/static of the transmission (like a scanner that doesn't have P25 decode), but it doesn't decode

It's possible you're getting strong enough interference on that frequency (or related harmonics) that it's interfering with the decoding.

 

[hotdjdave]

P25 Settings Cannot be Adjusted Individually

Try different decode settings. I think it makes more of a difference than people realize.

Even if I did find a better P25 setting, it doesn't matter because on the 396, the P25 settings are global for a each system. I cannot adjust the P25 settings for each channel, or even for each group. The P25 settings I have set are already optimum for the LAPD system (7 AUTO), or at least the best I can get it (still doesn't sound right - just have to live with that). So it's one setting fits all.

This make sense, since a radio system should have the same P25 settings globally across the system anyway. All the more reason why this is an issue. Why would one frequency/channel on a system have a P25 setting problem when all the others don't?

Thanks for the suggestion.

It's possible you're getting strong enough interference on that frequency (or related harmonics) that it's interfering with the decoding.

I am not sure that this would or should be an issue. Not knowing exactly how the P25 decode works, I don't know. There doesn't seem to be any interference, just the absence of the decoding of P25 transmissions. I am pretty sure this is the case because I can hear the transmission, just that it is not being decoded, like hearing it on a scanner that doesn't have P25 decode capabilities.

Thanks.

 

[SCPD]

Why would one frequency/channel on a system have a P25 setting problem when all the others don't?

Deviation issues on that particular repeater...

I run a P25 conventional system here. There are major differences in decode quality/settings if I adjust the deviation even just a few hundred kilocycles.

One perplexing issue I've noticed...

When I tweak my system so that packet loss is minimal for our real radios, (we're running a passive repeater, not a quantar) the scanner receives extremely poorly, no matter what settings I set it for.

ASTRO deviation should be 2.83 KHz, +/- 5%. LAPD techs may want to check that repeater out. You can check it too if you have a service monitor. There's also the issue of high/low tone balancing. This does affect ASTRO comm's. It's all part of the quantar/astro radio alignment.

Don't kidd yourself... there are a lot of clued-out technical people who work at REAL PS radioshops... It's quite possible (I don't know for sure obviously) that the repeater in question has been neglected for years.

Motorola ASTRO radios are much more forgiving to over/under-deviated/off-frequency ASTRO comm's. Uniden scanners are way too fussy. The PRO-96 is a lot more stable in this regard.