can't lock on P25 control channel

[dmdx86]

I apologize if this is an issue discussed previously; I couldn't find a thread on this particular type of issue.

I am trying to monitor the Richardson, TX P25 system with an outdoor discone and a 536HP. The system is imported from RR.

The scanner seems to have difficulty reading data from the control channel. The "DAT" indicator flickers intermittently on 852.2500Mhz. Much of the time it refuses to lock on the actual control channel and will continue searching all of the programmed frequencies for this site to try to find a usable control channel. This is all despite the fact that when it *does* briefly lock on this frequency, it gets 5 bars.

Occasionally it will lock long enough and read enough data from the control channel to know to tune into an active talkgroup and decode the voice data. The P25 voice decode is crystal clear every time. The control channel seems to be the problem.

On the same antenna, my 396XT can lock on the control channel on this system with no issues.

This is extremely frustrating as I bought the 536HP so (among other reasons) that I could decode the Plano, TX (PAWM) P25 system better. The 396XT is terrible on this system where I live, but the 536HP can decode that system almost flawlessly.

 

[N9NRA]

I apologize if this is an issue discussed previously; I couldn't find a thread on this particular type of issue.

I am trying to monitor the Richardson, TX P25 system with an outdoor discone and a 536HP. The system is imported from RR.

The scanner seems to have difficulty reading data from the control channel. The "DAT" indicator flickers intermittently on 852.2500Mhz. Much of the time it refuses to lock on the actual control channel and will continue searching all of the programmed frequencies for this site to try to find a usable control channel. This is all despite the fact that when it *does* briefly lock on this frequency, it gets 5 bars.

Occasionally it will lock long enough and read enough data from the control channel to know to tune into an active talkgroup and decode the voice data. The P25 voice decode is crystal clear every time. The control channel seems to be the problem.

On the same antenna, my 396XT can lock on the control channel on this system with no issues.

This is extremely frustrating as I bought the 536HP so (among other reasons) that I could decode the Plano, TX (PAWM) P25 system better. The 396XT is terrible on this system where I live, but the 536HP can decode that system almost flawlessly.

Intresting that you mention this, i`m having the same problem with my BCD436HP, did all the tests you did, even went as far as to reprogram by hand the band plan for the P25 system i was trying to test my new scanner out on (that`s how i noticed MY issue. Same symptoms as you, DAT ican flashes on& off and signal indicator dosen`t show a stable c-channel signal at all, so it`s not just you, i`m seeing this on my `436HP too. All we can do is report this and hope an update will come out to fix it. N9NRA P.S. My unit won`t even decode any TG`s at all, it finds control, but won`t lock on reliably enought to properly track. Like you i`m frustrated, and as like you my `396XT could lock & track without any problems, so i`m wondering if this is a scanner issue with these units.

 

[dmdx86]

Intresting that you mention this, i`m having the same problem with my BCD436HP, did all the tests you did, even went as far as to reprogram by hand the band plan for the P25 system i was trying to test my new scanner out on (that`s how i noticed MY issue. Same symptoms as you, DAT ican flashes on& off and signal indicator dosen`t show a stable c-channel signal at all, so it`s not just you, i`m seeing this on my `436HP too. All we can do is report this and hope an update will come out to fix it. N9NRA P.S. My unit won`t even decode any TG`s at all, it finds control, but won`t lock on reliably enought to properly track. Like you i`m frustrated, and as like you my `396XT could lock & track without any problems, so i`m wondering if this is a scanner issue with these units.

Thanks for your observations on this.

Like you, I even deleted and then re-created the site by hand with the information from RR. Didn't help.

I also went so far as to delete all of the frequencies out of the site except the frequency of the current active control channel so that the scanner wouldn't have any choice but to TRY to lock on that single frequency. This keeps the scanner form hopping around, but it still would only show the DAT icon intermittently whilst showing a solid 5 bars.

I tried changing from NFM to FM per UPMan's post and that didn't do anything for me. Even tried the attenuator - weaker signal (1-2 bars) but same behavior otherwise.

The other tips for changing the P25 adjust mode / threshold level don't apply here since this is control channel decoding, not actual P25 voice decoding.

When I get back to the house, I'm going to try (1) power-cycling, (2) using an indoor antenna, (3) a different power-supply, (4) disconnecting the serial port from the computer (in case any RF noise is getting into the unit). I'll update with results later.

 

[dmdx86]

Also, one of the things I did was to just manually tune into one of the voice frequencies and letting the scanner treat it as a conventional P25 frequency. The voice data decodes fine - no discernible distortion. Obviously this is not a usable solution since I can't track whole conversations this way.

 

[N9NRA]

Thanks for your observations on this.

Like you, I even deleted and then re-created the site by hand with the information from RR. Didn't help.

I also went so far as to delete all of the frequencies out of the site except the frequency of the current active control channel so that the scanner wouldn't have any choice but to TRY to lock on that single frequency. This keeps the scanner form hopping around, but it still would only show the DAT icon intermittently whilst showing a solid 5 bars.

I tried changing from NFM to FM per UPMan's post and that didn't do anything for me. Even tried the attenuator - weaker signal (1-2 bars) but same behavior otherwise.

The other tips for changing the P25 adjust mode / threshold level don't apply here since this is control channel decoding, not actual P25 voice decoding.

When I get back to the house, I'm going to try (1) power-cycling, (2) using an indoor antenna, (3) a different power-supply, (4) disconnecting the serial port from the computer (in case any RF noise is getting into the unit). I'll update with results later.

Good to hear i`m not the only one having this issue here, ya know i also had this with my `396XT after an update, which i believe is the SAME one that is on the x36 units right now, which i`m now thinkin` is a update bug. If you (or anyone else that`s done more testing on this) wants to, drop this onto the bug reports forum, you`re free to quote me if you need to. Mabey if enough of us make waves Uniden just MIGHT set an update to fix this, as right now the unit is not working in an acceptable condition for listening to P25 TRS`s, and just listening to one channel in conventional mode isn`t acceptable ether. Let`s get this out there so Upman at least sees this and can respond with some thoughts . N9NRA P.S. Fixed the issue on my `396XT by rolling the firmware back to the original version (the stock version that came on the unit), that would work...IF there were a way to do a rollback of these units, and unfortunately i can`t find any way to do it, mabey someone out here can ferret out that `un .

 

[brucewarming]

OK you may have different problems, #1 one of you is not getting a good signal. #2 The "DAT" icon will show data being transmitted, but your receive nothing. On problem #2....... The control channel is sending more data than just the voice signal. This could be frequencies not in your band plan. This could be data for a mobile digital data terminal. Depending on your scanner brand or model the scanner may Not hold on a data channel. Also there could be another "Band" plan also transmitting from the same tower with the same "Base" Frequency. So seeing the "DAT" icon and no voice is not always a problem.

 

[PiccoIntegra]

The other tips for changing the P25 adjust mode / threshold level don't apply here since this is control channel decoding, not actual P25 voice decoding.

Those adjustments aren't just for voice decoding. You can test those settings on a good P25 system control channel. Set the P25 Level to Manual(at the Site level), then scan, and put the radio in P25 display mode and turn the adjustments from 0 to 20. Watch the DAT message disappear.

Mabey if enough of us make waves Uniden just MIGHT set an update to fix this, as right now the unit is not working in an acceptable condition for listening to P25 TRS`s, and just listening to one channel in conventional mode isn`t acceptable ether. Let`s get this out there so Upman at least sees this and can respond with some thoughts .

Both the Uniden and GRE digital radios have had this problem since their inception. More than 10 years now?? My first and only digital scanner(and last) is the BCD996T. I didn't do my research before purchasing this radio, so that's on me. It's too bad all that energy from the wifi/app complainers aren't more vocal about poor digital decoding. It just goes to show what's important, bells and whistles are what sells.

I now use a $10 RTLSDR and a used $150 dual core laptop running linux with GNU Radio and OP25. I get perfect LSM control channel and voice decoding. There is no VAC/Unitrunker/SDR#/DSD nonsense to deal with either. None of those apps can decode LSM demodulation.

IF there were a way to do a rollback of these units, and unfortunately i can`t find any way to do it, mabey someone out here can ferret out that `un .

There is info in the Uniden section on how to do this, with links to the older firmware. Do a search for "firmware AND previous" under Uniden.

 

[N9NRA]

Those adjustments aren't just for voice decoding. You can test those settings on a good P25 system control channel. Set the P25 Level to Manual(at the Site level), then scan, and put the radio in P25 display mode and turn the adjustments from 0 to 20. Watch the DAT message disappear.


Both the Uniden and GRE digital radios have had this problem since their inception. More than 10 years now?? My first and only digital scanner(and last) is the BCD996T. I didn't do my research before purchasing this radio, so that's on me. It's too bad all that energy from the wifi/app complainers aren't more vocal about poor digital decoding. It just goes to show what's important, bells and whistles are what sells.

I now use a $10 RTLSDR and a used $150 dual core laptop running linux with GNU Radio and OP25. I get perfect LSM control channel and voice decoding. There is no VAC/Unitrunker/SDR#/DSD nonsense to deal with either. None of those apps can decode LSM demodulation.



There is info in the Uniden section on how to do this, with links to the older firmware. Do a search for "firmware AND previous" under Uniden.

You mean on the Uniden website or do a Google search? Reason i mention doing the "reverse movenent" thingy is when i had this same issue after an update of my `396XT i did just that, rolling back to the last good version (in that case the stock firmware that came on the scanner outta the box) which fixed the issue, that`s why i`m thinking rolling the firmware back to the last version is gonna be the ticket here. N9NRA

 

[PiccoIntegra]

You mean on the Uniden website or do a Google search?

I meant the Uniden section here in the RR forums.

See this post for more info on rolling back to previous firmware revisions.

 

[dmdx86]

Hey guys, just wanted to update with latest testing results. I was on vacation when I posted this (remote controlling through ProScan but no physical access to the scanner). I have physical access to it now that I am back.

(1) Power-cycled the 536HP. Unplugged the power supply from the back of the scanner, kept it off for about 30 seconds, then plugged everything back in and turned it back on. This did not change decoding performance.

(2) Removed audio cables, serial cables, USB cables from scanner that were plugged into computer. No change in performance.

(3) Removed the coax connection to the outdoor discone. Replaced it with the telescoping antenna that came with the 536HP. The signal is 2 bars with this antenna BUT it decodes the control channel more reliably - the DAT icon stays on about 70-80% of the time. As a result, I seem to be able to track active talk groups now.

(4) Plugged the outdoor discone into the 396XT. I get similar rotten performance on the 396XT (note - this used to work great on the 396XT!). Also, as in the case of the 396XT, it can decode other P25 control channels just fine, and it's okay with the local Motorola type II and EDACS systems. The 396XT can also decode P25 voice data just fine. All of the same statements apply to the 536HP.

Some information: I recently swapped out a section of coax (replaced a section of RG58/U that was being squeezed under a door with a section of LMR-200 that is coming in from outside thru a wall. While I am willing to entertain the possibility that this change somehow caused the problem, I find it unlikely given that no other system gives me any issues like this on either scanner.

Suspicion - Richardson made a change to their P25 system that negatively impacted control channel decoding.

Richardson is listed as having multiple simulcast sites - this system never gave me problems on the 396XT in the past (voice and control channel decoding were always reliable and crystal clear - no voice distortion like on the Plano system).

 

[dmdx86]

Next steps:

(1) Twiddle with the P25 Manual Adjust value. I'm not convinced this affects control channel decoding, but I'll give it a shot in case I'm wrong. I do want to note that when I press FUNC + VOL to show the ERR and other values, it never shows any ERR values when parked on the control channel (it just shows ---) which has what led me to believe those adjustments were for voice decoding only.

(2) Roll back firmware. I'm on 1.03.03. Is there a release that is recommended to roll back to?

(3) As a last resort, I'm willing to swap in a different section of coax cable and keep the entire run of coax outside for the duration of testing, just in case somehow I'm getting interference that may *possibly* be induced from nearby 120V AC lines in the wall. I'm not convinced this is the actual problem though since no other channel is giving these problems.

 

[JamesO]

Some information: I recently swapped out a section of coax (replaced a section of RG58/U that was being squeezed under a door with a section of LMR-200 that is coming in from outside thru a wall. While I am willing to entertain the possibility that this change somehow caused the problem, I find it unlikely given that no other system gives me any issues like this on either scanner.

You should not/cannot mix coax cable types on a cable run. This causes NOTHING but problems. There is a different rate of velocity between cables and when they do not match as well as having additional connectors/slices in the cable path you WILL have VSWR issues and this will cause all sorts of unexpected cable performance over different bands.

You would be MUCH better off with as single run of some decent RG-6 75 Ohm CATV even with some F connectors along with adapters than any cable mismatch that is spliced. This will cause peaks and valves in along the RF spectrum and will attenuate some frequencies.

Forget the LMR-200, you have a mess on your hands. Decent RG-6 double or quad shield will spank the mess you have now. RG6 will be about 1 dB better overall performance at 850 MHz than the LMR-200.

The RG6 will also likely be more robust than than the RG58 as well.

The section of LMR-200 is causing you big issues, get a solid run of RG6 installed and you will be far better off.

 

[dmdx86]

You should not/cannot mix coax cable types on a cable run. This causes NOTHING but problems. There is a different rate of velocity between cables and when they do not match as well as having additional connectors/slices in the cable path you WILL have VSWR issues and this will cause all sorts of unexpected cable performance over different bands.

You would be MUCH better off with as single run of some decent RG-6 75 Ohm CATV even with some F connectors along with adapters than any cable mismatch that is spliced. This will cause peaks and valves in along the RF spectrum and will attenuate some frequencies.

I'll take your word - I'm not an EE. Do understand that there is no "splicing" involved in this setup.

So here's what I'll do - I'll unhook the drop of coax that directly feeds my discone and hooks into my lightning arrestor. The setup looks like this:

Discone <-> LMR-400 <-> Lightning Arrestor <-> LMR-200 <-> Scanner

I'll take the 536HP outside, hook it up directly to the other end of the LMR-400 (will need to purchase an adapter first since it has a UHF connector) and see if the problem persists.

I don't believe this is the issue for the reasons I stated but I do want to rule it out.

 

[JamesO]

I'll take your word - I'm not an EE. Do understand that there is no "splicing" involved in this setup.

So here's what I'll do - I'll unhook the drop of coax that directly feeds my discone and hooks into my lightning arrestor. The setup looks like this:

Discone <-> LMR-400 <-> Lightning Arrestor <-> LMR-200 <-> Scanner

I'll take the 536HP outside, hook it up directly to the other end of the LMR-400 (will need to purchase an adapter first since it has a UHF connector) and see if the problem persists.

I don't believe this is the issue for the reasons I stated but I do want to rule it out.

Mis-match of cabling is not a good idea. You will be better off either running a full LMR-400 run, but not sure the cost. I run RG6 for most of my applications, if needed, I will put a LNA in after the antenna if the cable loss really is a problem.

The LMR-200 is nothing but an attenuator after the LMR-400. Think of this set up as a 1/2" water pipe then transitioned into a 1/4" water pipe. Nothing good will come of this at the end of the day when you try to take a shower or do your laundry. It would be just fine for your ice maker in the freezer. As a test if can hook the scanner up directly to the LMR-400 this will pretty much answer your question.

If not, get some RG6 and some adapters and even use the RG6 as a test drop if you cannot get the scanner directly to the LMR-400.

Yes, the LMR-400 is better than the RG-6, but it comes down to budget and availability. RG-6 is overall very easy to work with, has cheap F connectors and although adapters are not a great idea, they work reasonably well in a receive antenna set up.

 

[PiccoIntegra]

(1) Twiddle with the P25 Manual Adjust value. I'm not convinced this affects control channel decoding, but I'll give it a shot in case I'm wrong. I do want to note that when I press FUNC + VOL to show the ERR and other values, it never shows any ERR values when parked on the control channel (it just shows ---) which has what led me to believe those adjustments were for voice decoding only.

The radio doesn't display the error rate when decoding the control channel, just the voice packets. However, the voltage levels DO affect the CC decoding...

 

[detroit780]

LMR-400

Except you are mismatching with RG-6 and a scanner.
RG-6 is 75 ohm coax and scanners use 50 ohm coax.

RG-6 loss is 6 dB per 100 feet at 900 MHz (75 Ohm)
LMR-400 is 4.1 dB per 100 feet at 900 MHz (50 Ohm)

Probably not much difference if you keep the jumper relativly short.

http://rfelektronik.se/manuals/Datasheets/Coaxial_Cable_Attenuation_Chart.pdf

Mis-match of cabling is not a good idea. You will be better off either running a full LMR-400 run, but not sure the cost. I run RG6 for most of my applications, if needed, I will put a LNA in after the antenna if the cable loss really is a problem.

The LMR-200 is nothing but an attenuator after the LMR-400. Think of this set up as a 1/2" water pipe then transitioned into a 1/4" water pipe. Nothing good will come of this at the end of the day when you try to take a shower or do your laundry. It would be just fine for your ice maker in the freezer. As a test if can hook the scanner up directly to the LMR-400 this will pretty much answer your question.

If not, get some RG6 and some adapters and even use the RG6 as a test drop if you cannot get the scanner directly to the LMR-400.

Yes, the LMR-400 is better than the RG-6, but it comes down to budget and availability. RG-6 is overall very easy to work with, has cheap F connectors and although adapters are not a great idea, they work reasonably well in a receive antenna set up.

 

[JamesO]

Except you are mismatching with RG-6 and a scanner.
RG-6 is 75 ohm coax and scanners use 50 ohm coax.

RG-6 loss is 6 dB per 100 feet at 900 MHz (75 Ohm)
LMR-400 is 4.1 dB per 100 feet at 900 MHz (50 Ohm)

Probably not much difference if you keep the jumper relativly short.

http://rfelektronik.se/manuals/Datasheets/Coaxial_Cable_Attenuation_Chart.pdf

I am TOTALLY aware that RG6 is 75 Ohm and is a "Mismatch". A single mismatch using 75 Ohm coax for the entire cable run is nowhere near as BAD as using different version of cable on a run. The ABSOLUTELY worst situaiton is where there would be a cable run that has something link LMR-400, then a transition to LMD-200, then a transition back to LMR-400. Anytime you have cable "A", then cable "B", then cable "A" you will have a REAL mess on your hands.

Again, the best cable runs use the same product from end to end.

BUT, any time you mix different cables, even of the same impedance, there is a difference in Velocity of Propagation as well as loss and this mixing of cables will cause all some very unexpected and unpredictable performance.

But what you need to realize I have been running 75 Ohm RG6 for over 25 years in MANY, MANY receive applications without any major problems. RG-6 is cheap, readily available, connectors are easy to get and install, many antennas have 75 Ohm baluns with F connectors, lower noise distribution Amplifiers are cost effective and readily available. So do not knock RG6 and 75 Ohm passives and Amplifiers until you try it.

 

[N9NRA]

Thanks for your observations on this.

Like you, I even deleted and then re-created the site by hand with the information from RR. Didn't help.

I also went so far as to delete all of the frequencies out of the site except the frequency of the current active control channel so that the scanner wouldn't have any choice but to TRY to lock on that single frequency. This keeps the scanner form hopping around, but it still would only show the DAT icon intermittently whilst showing a solid 5 bars.

I tried changing from NFM to FM per UPMan's post and that didn't do anything for me. Even tried the attenuator - weaker signal (1-2 bars) but same behavior otherwise.

The other tips for changing the P25 adjust mode / threshold level don't apply here since this is control channel decoding, not actual P25 voice decoding.

When I get back to the house, I'm going to try (1) power-cycling, (2) using an indoor antenna, (3) a different power-supply, (4) disconnecting the serial port from the computer (in case any RF noise is getting into the unit). I'll update with results later.

Well, ya might be intrested to know that i think i`ve found a workaround to this, what i ended up doing was to switch the modulation from NFM to plain FM...and i got flawless lock & track . One note, seems with the `436HP at least. one cannot change this setting and have it stay, turnning the unit off then back on sets it back to the defualt (in this case NFM). Seems the bug appears only in the NFM mode for some reason. Kinda curious now, but is there a way to change the modulation setting for a P25 trunked system or am i stuck with this way of doing things? Reason i ask is if i can change it then i`ve found the workaround to this bug...i hope . N9NRA

 

[phask]

Hey James - how do I fit this 2" hard line on to my HP


I know all the theory - BUT I cn rarely HEAR any difference nor discern any reduction in reception , not I said reception, using nearly ANY coax on a scanner. And I have used them all in the last 40 years. I've used matched, un-matched, added baluns,etc. Unless one is chasing very weak signals I maintain it's not applicable.

On transmit - that is another ballgame.

I am TOTALLY aware that RG6 is 75 Ohm and is a "Mismatch". A single mismatch using 75 Ohm coax for the entire cable run is nowhere near as BAD as using different version of cable on a run. The ABSOLUTELY worst situaiton is where there would be a cable run that has something link LMR-400, then a transition to LMD-200, then a transition back to LMR-400. Anytime you have cable "A", then cable "B", then cable "A" you will have a REAL mess on your hands.

Again, the best cable runs use the same product from end to end.

BUT, any time you mix different cables, even of the same impedance, there is a difference in Velocity of Propagation as well as loss and this mixing of cables will cause all some very unexpected and unpredictable performance.

But what you need to realize I have been running 75 Ohm RG6 for over 25 years in MANY, MANY receive applications without any major problems. RG-6 is cheap, readily available, connectors are easy to get and install, many antennas have 75 Ohm baluns with F connectors, lower noise distribution Amplifiers are cost effective and readily available. So do not knock RG6 and 75 Ohm passives and Amplifiers until you try it.

 

[N9NRA]

Good news folks! I can report that i`ve found a workaround to the problem of no lock on c-channels at least on the `436HP. What i did was to go into MENU>SETTINGS> band defaults, change any (or all) of these from NFM to FM, did this with the system i was monitoring (a P25 trunked system) and now have stable lock & track, will test further, but for now it appears that this issue affects reception of P25 TRS`s in the NFM mode only. I`ll update later on with the results . N9NRA