Abysmal 436 P25 Signal

[fmalloy]

Moved from a 346XT to a 436HP because my city migrated from analog 800MHz Mot II trunking to 700MHz P25 Phase II. With other variables the same - same location, same rubber duck antennas (800MHz Laird Antenex and stock) same distance to the tower (3 mi) - the signal goes from 4 full bars and strong, clear audio on the 346 to 1-2 bars and almost non-existent P25 calls on the 436. The radio is mostly silent on P25. The few calls I hear are almost always choppy and completely unintelligible.

My scanner is 3 feet from a window and just a few miles from the tower. I'm right in the city I'm trying to receive (Santa Clara, CA, SVRCS system). Never had any reception problems from the 346XT. I got all my city plus all the neighboring cities.

Why would I get a strong 800MHz control channel on the old scanner, and lousy signal on 700MHz P25 control channels? The scanner and tower locations were identical before and after the switch.

Need help!

 

[budevans]

Moved from a 346XT to a 436HP because my city migrated from analog 800MHz Mot II trunking to 700MHz P25 Phase II. With other variables the same - same location, same rubber duck antennas (800MHz Laird Antenex and stock) same distance to the tower (3 mi) - the signal goes from 4 full bars and strong, clear audio on the 346 to 1-2 bars and almost non-existent P25 calls on the 436. The radio is mostly silent on P25. The few calls I hear are almost always choppy and completely unintelligible.

My scanner is 3 feet from a window and just a few miles from the tower. I'm right in the city I'm trying to receive (Santa Clara, CA, SVRCS system). Never had any reception problems from the 346XT. I got all my city plus all the neighboring cities.

Why would I get a strong 800MHz control channel on the old scanner, and lousy signal on 700MHz P25 control channels? The scanner and tower locations were identical before and after the switch.

Need help!

fmalloy,

Based on your account and a quick look at the SVRCS system my best guess is that you are experiencing a Simulcast issue. The RR database lists one Site with two locations, with one set of frequencies. That combined with the wide variations in signal strength are indicators typical of LSM distortion issues common to many P25 Simulcast systems.

The prior Moto Type II (analog) system was probably a Multicast setup. Each transmitter location had it's own set of unique frequencies. So they didn't interfere or cancel each other out.

FYI: The 436 in my experience handles P25 Simulcast distortion far better than my other P25 scanner (GRE PSR-500).

Per what I've read on the Uniden forums, the 436 has P25 settings that can be adjusted. Those adjustments might improve your situation. I don't have any experience with those settings, so I'll stop here.

Hopefully others will respond to give you a hand.

 

[fmalloy]

Would simulcast distortion cause a low signal level as displayed on the bars? That seems to be my issue - low signal. In the same room with the same antenna, analog on the 346 gave a strong, clear signal at 800MHz Mot II. Now the same agency went 700MHz P25 and I get 0-2 bars, max. The display says "DAT" while ID scanning but calls rarely come through. When they do, they're garbled and choppy. Unintelligible. On the ultra-rare occasion I got readable audio.

I took the scanner outside my house in the clear and the signal level did not improve.

I'm going to try a few more days but if I can't figure anything out the scanner is getting returned and I'm going back to my 346XT where at least I can hear the analog agencies (which are much farther away). I am NOT erecting an outdoor antenna just to pick up my local city's PD/FD where the tower is literally 3 miles away.

I'm angry because my city came in so clear before they went P25. Only two things have changed: Analog to P25, and 346XT to 436HP. If I got a lousy signal before then I would expect a lousy signal now. But this kind of degradation is unacceptable to me.

If they are moving to P25 to frustrate scanner owners and don't want them listening to their transmissions, well "mission accomplished".

I have a feeling that's what P25 was ultimately designed for. You don't even need encryption - with P25 it sounds encrypted anyway.

 

[phask]

May not apply - but the statewide system in Ohio is undergoing similar - the 700 freqs. on the same tower have much lower strength.

Verified with Band Scope feature on HP2 extreme.

Not Ph2 ,though has the capability - nor is it simulcast.

 

[fmalloy]

May not apply - but the statewide system in Ohio is undergoing similar - the 700 freqs. on the same tower have much lower strength.

Thank you for this info, it's helpful!

But...why on EARTH would they supply a lower strength signal for P25 when digital (clearly) needs a stronger signal so bits aren't dropped? Or is the 700MHz receive on the Unidens less sensitive?

This technology is clearly a case where digital is NOT better. The old saying comes to mind...if it 'aint broke don't fix it...

 

[kayn1n32008]

Thank you for this info, it's helpful!



But...why on EARTH would they supply a lower strength signal for P25 when digital (clearly) needs a stronger signal so bits aren't dropped? Or is the 700MHz receive on the Unidens less sensitive?



This technology is clearly a case where digital is NOT better. The old saying comes to mind...if it 'aint broke don't fix it...

My guess, if I am looking at the correct location: http://www.radioreference.com/apps/db/?sid=7804

Is that this is a simulcast system. If it is using CQPSK(LSM) then likely this is your problem. Scanners do not have a receiver designed to receive CQPSK.


Sent from my iPad using Tapatalk

 

[fmalloy]

My guess, if I am looking at the correct location: Silicon Valley Regional Communications System (SVRCS) Trunking System, , California - Scanner Frequencies

Is that this is a simulcast system. If it is using CQPSK(LSM) then likely this is your problem. Scanners do not have a receiver designed to receive CQPSK.

Yes, that is the correct system (SVRCS)

I haven't heard about CQPSK or being incompatible with scanners. I have heard of people in the area who are receiving transmissions but for some reason I cannot.

These issues (CQPSK, multicast, etc.) seem very basic and without putting a highly directional antenna on my roof I'm not going to receive anything.

Guessing the 436 is destined to be returned...

 

[troymail]

Two comments -

1. Newer systems are (or at least seem to) emit at a lower power and the radiation patterns are tweaked/tuned to generally stay within the area they are designed to cover.

2. If the system is using digital/simulcast (i.e. more than one tower/transmitter site) - and most do, when it comes to scanner's your reception will vary -- it all comes down to location (just inches can make a huge difference).

Uniden has said all along - even with the x36 radios - YMMV ("your milage may vary").

 

[fmalloy]

1. Newer systems are (or at least seem to) emit at a lower power and the radiation patterns are tweaked/tuned to generally stay within the area they are designed to cover.

Thank you. Don't know why they'd emit a lower power, but whatever.

I am in the area the tower is designed to cover. It's just 3 miles away and there is no other tower closer.

2. If the system is using digital/simulcast (i.e. more than one tower/transmitter site) - and most do, when it comes to scanner's your reception will vary -- it all comes down to location (just inches can make a huge difference).

Uniden has said all along - even with the x36 radios - YMMV ("your milage may vary").

I've moved the scanner all over the house, and took it outside. No change in signal strength. I'm going to walk around the neighborhood, maybe get in the car.

One thing is for sure - P25 digital is super sensitive and very very scanner listener-unfriendly.

In the end, i'm going to send back the 436 and stick to analog until the entire area is swallowed by the growing P25 system, then find another hobby.

 

[kayn1n32008]

Yes, that is the correct system (SVRCS)

I haven't heard about CQPSK or being incompatible with scanners. I have heard of people in the area who are receiving transmissions but for some reason I cannot.

These issues (CQPSK, multicast, etc.) seem very basic and without putting a highly directional antenna on my roof I'm not going to receive anything.

Guessing the 436 is destined to be returned...

It has to do with limitations of the discriminator tap used to feed the vocoder, C4FM is fine. I believe slicerwizard wrote up a description of the issue when the x36 scanners were released. It is kind of foggy, if i remeber right it had to do with the symbol decision points of the CQPSK wave form and filtering that messed it up.

 

[fmalloy]

It has to do with limitations of the discriminator tap used to feed the vocoder, C4FM is fine. I believe slicerwizard wrote up a description of the issue when the x36 scanners were released. It is kind of foggy, if i remeber right it had to do with the symbol decision points of the CQPSK wave form and filtering that messed it up.

Thanks. This is way over my head.

I know other folks in my area have been able to receive this system, so I suspect it's just my exact location within the whole multicast set that is bad.

I repeat - I'm 3 miles from the tower and the meter shows 1 or 2 bars, and I get almost no calls, and the ones I do are so garbled they're unintelligible.

I'm going to drive around and see if there is anywhere I can receive this system.

460MHz/170MHz/800MHz analog comes booming in from 10+ miles away.

Guess P25 doesn't like me, and I don't like it.

 

[whisper16]

Don't give up

Have you tried turning on the Attenuator? As close as you are to the tower there is a chance you may be overloading the scanner. I know it sounds like just the opposite thing to do with what the problem is but it's worth a try.

Also did you try the P25 adjustments on the 436 that another member suggested ?

As you stated other members have posted that they have no issues, and both the live feed for SCPD and SVDPS sound good, so the system can successfully be monitored.

 

[budevans]

Thanks. This is way over my head.

I know other folks in my area have been able to receive this system, so I suspect it's just my exact location within the whole multicast set that is bad.

I repeat - I'm 3 miles from the tower and the meter shows 1 or 2 bars, and I get almost no calls, and the ones I do are so garbled they're unintelligible.

I'm going to drive around and see if there is anywhere I can receive this system.

460MHz/170MHz/800MHz analog comes booming in from 10+ miles away.

Guess P20 doesn't like me, and I don't like it.

The signal strength readings (RSSI) from the 436 have been found to show lower readings. That doesn't mean you are getting less signal, it means the programming in the scanner for the RSSI signal strength is different that it was in other scanners.

In my case there are three trunk systems in neighboring counties that come in perfectly with no bars showing on the 436. The same systems read 3 to 4 bars on my GRE-500. When I first saw no bars for those systems I thought (as many did) that my scanner was deaf. But it receives the exact same traffic as the GRE-500.

So take the 0 - 2 bars with a grain of salt. The low RSSI readings have been reported in several Uniden threads.

 

[fmalloy]

Have you tried turning on the Attenuator? As close as you are to the tower there is a chance you may be overloading the scanner. I know it sounds like just the opposite thing to do with what the problem is but it's worth a try.

Also did you try the P25 adjustments on the 436 that another member suggested ?

As you stated other members have posted that they have no issues, and both the live feed for SCPD and SVDPS sound good, so the system can successfully be monitored.

Thank you! This is helpful and I will try it. I'm desperate. Not trying to be negative; I want to like this scanner and I want to receive Santa Clara city PD/FD on the new SVRCS system.

I will try turning on attenuation (it's easy) but you'd think if it was overloaded the strength indicator would be pegged...anyway, will give a go.

I will play with the P25 settings, but I have no idea what to set them to. Well, I can't get reception any worse than it is now...

Thanks again!

 

[fmalloy]

The signal strength readings (RSSI) from the 436 have been found to show lower readings. That doesn't mean you are getting less signal, it means the programming in the scanner for the RSSI signal strength is different that it was in other scanners.

In my case there are three trunk systems in neighboring counties that come in perfectly with no bars showing on the 436. The same systems read 3 to 4 bars on my GRE-500. When I first saw no bars for those systems I thought (as many did) that my scanner was deaf. But it receives the exact same traffic as the GRE-500.

So take the 0 - 2 bars with a grain of salt. The low RSSI readings have been reported in several Uniden threads.

Thanks Bud that is interesting to know and very helpful.

Sadly, I still think there's a signal issue, because not many transmissions come in from my local PD/FD (I got much, much more traffic when they were analog) and when they come in they are choppy, garbled, and cut off. A couple of questions:

1. When it says "ID Scanning...", the "DAT" indicator is on steady, sometimes flickers but is usually on pretty solid. If this is displayed, doesn't it mean the 436 is receiving data, which would indicate a decent signal?

2. How do you turn on the error rate indicator? When I get a transmission, I'd like to see how many errors are happening. It must be a lot, since the audio is so garbled.

Thanks to everyone for their help.

 

[Bucko]

On my 536 you press hold, (don't have a 436) then push func then the volume. For the simulcast system in my county I had bad distortion and choppy transmissions. I played with P25 on county simulcast system setting it to manual and at 7 seemed to give the lowest error rate.

 

[fmalloy]

Have you tried turning on the Attenuator? As close as you are to the tower there is a chance you may be overloading the scanner. I know it sounds like just the opposite thing to do with what the problem is but it's worth a try.

Turned on the attenuator and got no signal, and lost the "DAT" on the display, and zero audio heard.

I walked around the neighborhood, and once I get out of the house and 30 yards away, the signal improves.

 

[fmalloy]

On my 536 you press hold, (don't have a 436) then push func then the volume. For the simulcast system in my county I had bad distortion and choppy transmissions. I played with P25 on county simulcast system setting it to manual and at 7 seemed to give the lowest error rate.

Thanks! It worked for the 436. On your average short call I get 10 errors. At the bottom it shows:

T 1.45 1.65 1.84

Don't know what that means...

 

[whisper16]

Threshold levels

Those numbers are the lo, mid, and high P25 decode levels. The level numbers are an index into a table of thresholds for decoding the digital data. Higher numbers are more permissive (the thresholds for decoding are wider) while smaller numbers tighten the threshold ranges. The optimum range depends on how the technicians have set up the system you are trying to receive. The numbers change when you change the setting number 0-20.

I would try going through the 0-20 settings and see which one gives you the best reception. You want the lowest error rate.

 

[fmalloy]

Those numbers are the lo, mid, and high P25 decode levels. The level numbers are an index into a table of thresholds for decoding the digital data. Higher numbers are more permissive (the thresholds for decoding are wider) while smaller numbers tighten the threshold ranges. The optimum range depends on how the technicians have set up the system you are trying to receive. The numbers change when you change the setting number 0-20.

I would try going through the 0-20 settings and see which one gives you the best reception. You want the lowest error rate.

Thank you!

If higher numbers are more permissive, would it make sense to try that first? What if I set them all to 20? What would happen? Would small values mute the audio more easily, and high values cause distorted, garbled audio because it's trying to decode garbage?

The thing about analog - with noise and bad signal, the human ear and our incredible brains can still pick out and understand words. With digital, you lose bits, and they're gone forever and the audio is non existent or mis-decoded to something completely unintelligible. That's bad.

Digital is fantastic when you have a reliable medium of transmission (satellite, CDs, wire) but public service radio? A mess...