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Uniden Owner Tech Support For current owners to get support with their scanners from existing or past owners. If you do not own or have model experience please restrict yourself to the other sub-forums.

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  #61 (permalink)  
Old 11-21-2013, 12:21 PM
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Quote:
Originally Posted by AZScanner View Post
In regards to the lower squelch helping P25 decoding, hell I noticed that with my old BC250D back when the Phoenix digital system was first being tested! On my trusty old BC796D, the squelch is set all the way wide open. Works pretty good that way, too.

Here in Phoenix where we have the RWC (which stands for Simulcast Radio System from Hell ) the best solution to this problem has been to put up a Yagi antenna and position it so that signals are only coming from ONE site. Once you do that, it comes in very very well. Not quite perfect, but considering the fact that you can buy a decent Yagi for less than 50 or build one yourself for less than 20, good enough.

If you want mobile use, set up your scanner on a yagi anyway, and become a feed provider so you can listen to your scanner anywhere you have cell service on your smartphone.

-AZ
Hi AZScaner: I have some answers and a permanent fix for this issue. You will have to P/M for it. Its a great fix and you will learn a lot but worth it. Let me know. I heard AZ has had problems with their Simulcast issues. It will be a fun project for you to take on unless you already are happy with your yagi antenna work around.
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  #62 (permalink)  
Old 11-22-2013, 9:23 AM
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Default Re: Loose (Open) Squelch Improves LSM (Simulcast) Reception

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Originally Posted by 3MTA344 View Post
Hi AZScaner: I have some answers and a permanent fix for this issue. You will have to P/M for it. Its a great fix and you will learn a lot but worth it. Let me know. I heard AZ has had problems with their Simulcast issues. It will be a fun project for you to take on unless you already are happy with your yagi antenna work around.
Why not just post it on here so other members who may have the same issue can benefit from it?

Sent from my C570 using this tapatalk machinery
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  #63 (permalink)  
Old 11-22-2013, 11:36 AM
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  #64 (permalink)  
Old 11-22-2013, 11:46 AM
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I have a feeling that 3MTA344 does not want to give any public attention to the methods used. I can respect that. I'm sure if you send a PM to him as well, your curiousity can be satisfied. I have sent one with the caveat that whatever he decides to share with me will be kept in confidence. If you take a peek at his shack photos, I'm sure you can make an educated guess as to how he has solved this particular problem.

-AZ
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  #65 (permalink)  
Old 11-22-2013, 3:24 PM
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Uh oh... banned? I guess I shouldn't expect a PM anytime soon then...

-AZ
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Old 11-22-2013, 3:29 PM
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Uh oh... banned? I guess I shouldn't expect a PM anytime soon then...

-AZ
At least the "shack" photos are still viewable.
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  #67 (permalink)  
Old 11-22-2013, 3:35 PM
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Ok, so can someone explain why that user was banned?
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  #68 (permalink)  
Old 11-22-2013, 3:36 PM
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At least the "shack" photos are still viewable.
LOL yeah but will those two women in his "shack" properly decode LSM/CQPSK P25 digital? I'm guessing "no".

Quote:
Originally Posted by phillydjdan View Post
Ok, so can someone explain why that user was banned?
My guess is that Paul sent in the Men in Black to silence him before he spilled the beans on how to fix LSM issues without buying a new scanner.

-AZ
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Last edited by AZScanner; 11-22-2013 at 3:38 PM..
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  #69 (permalink)  
Old 11-22-2013, 6:42 PM
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Quote:
Originally Posted by UPMan View Post
I will add that I do not know whether the squelch setting will result in performance changes for GRE scanners. Probably worth the experiment. Here is a sample setup for checking (requires two of the same model).

Connect both scanners to the same antenna, preferably through a multicoupler, but it is probably possible to do this with direct connections. The goal is really just to ensure that both scanners are getting exactly the same signal.

Tune both scanners to the same digital channel and hold on the channel.

Fully open squelch on one scanner. Set the other scanner at/near the squelch threshold.

Compare results between the scanners.
I have the 396xt and psr800. I have a issue with the psr800 not picking up the p25 with the squelch open, closed, and halfway still won't pick up. The 396xt picks it up with no problem. Both radios are the RS800 antenna.
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Old 11-24-2013, 9:39 AM
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Quote:
Originally Posted by AZScanner View Post
If you're struggling with simulcast hell, try using FM along with a loose squelch. It won't be a huge improvement, mind you, but it will help.

-AZ
I had never thought of FM vs. FM Narrow before. Switched my PRO-106 to "Narrow FM: No" and now I have nearly 100% copy on the Starcom 21 Wauconda talkgroups I monitor. It's the single biggest improvement I've made after trying everything in the dozens of posts here on simulcast reception!

Thanks for the tip AZ!
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  #71 (permalink)  
Old 11-24-2013, 7:48 PM
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Default Loose (Open) Squelch Improves LSM (Simulcast) Reception

Hmmm...now I'm really anxious to try switching off NFM on my BCD386XT to see if that helps.
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  #72 (permalink)  
Old 11-24-2013, 11:00 PM
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I tried switching from NFM to FM on my BCD996XT and it made no difference. I'm monitoring the ORION system from just outside the Omaha city limits. The signal strength has always been 5 bars but very broken up at times, especially if it's windy outside. I sure hope Uniden comes up with another firmware fix.
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  #73 (permalink)  
Old 11-25-2013, 12:18 PM
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Hi gang,

As you can see, mileage will vary on the NFM to FM trick. It seems to help on my end when monitoring the Phoenix RWC, but not a whole lot. There's only so much these scanners can do. Much of how they receive (or not) on these systems depends on location, type of antenna, rx mode used, etc. The fact that my particular scanner (the BC796D) is old enough to be a museum piece doesn't help either.

Something else I noted on my scanner years ago was that for some reason when trunking it doesn't decode as well as it does when just conventionally scanning the frequencies. I've yet to try this experiment, but I'm thinking I might run the scanner as a conventional voice scanner on Unitrunker and let Unitrunker parse the data channel rather than the scanner itself to see if that makes any difference. I'm also thinking about having a look at the firmware data from the latest update to see if by chance there's a way to open up 700MHz on my old BC796D so I could monitor some of our other simulcast sites that exist solely on 700Mhz. The scanner is far beyond it's warranty and even though it was never type accepted to tune 700MHz, I fail to see the harm in opening that band up on my own if the firmware will allow it. I'll have to examine the contents of the firmware update file in a hex editor and see if I can recognize where the band settings are loaded, but that's for another thread later on if I can get it to work.

-AZ
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  #74 (permalink)  
Old 11-25-2013, 12:21 PM
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Default Loose (Open) Squelch Improves LSM (Simulcast) Reception

Wow, AZ! That's the spirit! Let us know how it goes!
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  #75 (permalink)  
Old 11-29-2013, 7:43 PM
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Quote:
Originally Posted by AZScanner View Post
how to fix LSM issues without buying a new scanner.

-AZ
It is possible (in theory) to modify a scanner to fix the simulcast distortion problem in a proper way.

Before even considering this for a particular unit it would be necessary to confirm clean oscillation with low phase noise for all of the LO's in the scanner - in practice it's usually only necessary to check the first LO (e.g. using a good UHF receiver, in CW mode, tuned near the frequency of the first LO, with a pickup loop antenna placed near the scanner under test). If the tone is raspy or jumpy, forget about it.

Next it's necessary to check the scanner's final IF filter (usually a ceramic filter with a part number such as CFx-455x made by MuRata or Rubycon etc) for excessive group delay distortion. This problem can be worsened if the target signal is not exactly tuned in the center of the passband of this filter.

The cause of the simulcast distortion problem in scanners is known and has been isolated to the FM demodulator stage (aka PLL/discriminator). When CQPSK with additive simulcast distortion is applied to any FM demodulator (or discriminator etc). the resulting mangled signal cannot be properly decoded and the correct signal can no longer be recovered.

The solution is to demodulate the signal as (D)QPSK, not as C4FM. This must be done at IF , i.e., *prior to* the FM demodulator (see previous paragraph), with the result that the simulcast distortion is removed (there is a limit to how much, which applies just as well to "real" user radios in the system).

So the steps to modify our hypothetical scanner would be
* tap the last IF (either immediately before or after the C.F., see above)
* demodulate the signal (typically 455 KC) using the [D]ifferential QPSK method
* use the result of the previous step to C4FM-modulate an FM carrier signal (at 455 KC)
* apply this regenerated "IF" signal to the next stage after where we interrupted the signal flow (first step above)

As an exercise, for extra credit:
* allow the above mod to be switched out, when non-P25 signals are received
* perform FEC (forward error correction) based on soft-decision information from the DQPSK symbols

Practially speaking, we should be demanding scanners that handle this correctly. All it takes is IF DSP - already a very common feature in ham equipment. UPMan - are you listening ?

73

Max
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  #76 (permalink)  
Old 11-29-2013, 8:41 PM
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Hi Max,

Do you think that a circuit can be developed to do what you said above and be installed inside a radio?
That would be an awesome project! GRE scanners use 455KHz IF for the final stage so a PSR600/PRO-197 should be a good candidate since it would be easier to perform the taps than a portable like PSR800.

It would be great if we can get a group together for the project. There's plenty of knowledge here on RR. I can design the board, get it manufactured and source it out for component placement. I am not great soldering anymore, especial SMT.

So I assume this would need to be done in a DSP environment to demodulate and remodulate the IF, correct?
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Old 11-29-2013, 8:49 PM
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I agree......UPMan are you listening? But can your resolution be applied to a BCD996XT with a firmware upgrade?
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Old 11-29-2013, 8:53 PM
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as usual the thread takes a compleetly different direction and is answered in a manner that only someone who works on scanner s can understand i agree the HP1 should not have this problem I,am not happy i paid 500 dollars for what amounts to a paper wait at times but Mike your answer is greek to me i appericeate the effort what i need is to be able to contact the live provider and see what they did to fix it
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Old 11-29-2013, 9:00 PM
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Max if you think this is a doable project, maybe I can get a thread started in a more appropriate forum.
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  #80 (permalink)  
Old 11-30-2013, 11:12 AM
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Hi Max,

Do you think that a circuit can be developed to do what you said above and be installed inside a radio?
Yeah, of course, again in theory. The cheapest way may be to employ frequency conversion to get the IF's down into the audio range to allow the use of soundcard style DSP. I use a nominal IF value of 24 KHz. The actual DSP would need to be full duplex, of course.

Quote:
So I assume this would need to be done in a DSP environment to demodulate and remodulate the IF, correct?
This is of course correct but insufficient. For example the mod outlined (previously) does a severe butchery to our hypothetical scanner's AGC loop - the designer would need to address this issue as well as the general issue of getting AC signal levels correct at all points...

I have written (and published as Free Software) all of the software building blocks that would be needed to build such a "device", including the Gardner DQPSK demod block (which has been tuned to work with CQPSK) and the C4FM modulator block (know me as a midget who stands on the shoulders of the true giants, the authors of GNU Radio and Python and all the rest, without which our [OP25] software would not be possible)... Nonetheless this stuff is not going to fit into (say) an 8051 today or tomorrow...

Personally I have zero interest in a project such as this. The current generation of scanners are all total junk -
* RF/intermod performance is pathetic
* programming interfaces are obfuscated [GRE for sure, and last I looked Uniden but it was a while]
* the radio firmware is treated as secret and the user cannot change features if desired
* users utterly dependent on the mercies of the centralized DB feed
* obviously, the issue of LSM/CQPSK in and of itself
* but - the fact that they can't fix LSM with just a software update - should be viewed as unacceptable
[ in this day and age *all* this stuff is done in software. Why not scanners? ]
* finally, prices are extremely uncompetitive when measured against comparable SDR hardware

Haha, end of rant

73

Max
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