The official "I want LSM to work properly in my scanner" thread

[KA1RBI]

But even with AMBE Vocoders, the X36's still do not even compare to say an APX on an P25 LSM system.

Several logic errors here - all scanners that support P25 use codecs supplied by the single-source vendor, DVSI. Are you saying that DVSI reserves their best-sounding codecs, and sell them only for use in APX radios? How do you know that the problem with the X36 is specifically in the vocoder stage, and not in some other stage (for example in the demodulator)?

Max

 

[slicerwizard]

The older scanners use IMBE, the X36's use AMBE.

Oh jeebus. So this is how this nonsense gets started...

Older scanners use IMBE because that's what Phase I P25 audio uses. You know - the only digital voice protocol that those older scanners can decode.

Newer scanners use IMBE *and* AMBE+2, because they can handle P25 Phase I audio (IMBE) and P25 Phase II audio (AMBE+2). They decode both protocols, so they use both codecs.

LSM systems are usually using AMBE with Phase II ones using AMBE II.

I'll just point out that you're suggesting that simulcast systems with Phase I talkgroups use AMBE for voice data, rather than IMBE, which would be a gross violation of the P25 standards.

And no P25 system, LSM or otherwise, uses "AMBE" or "AMBE II". They use IMBE for Phase I voice and AMBE+2 for Phase II voice.

Further, LSM, or lack of LSM, has nothing to do with codecs. LSM, which is a hybrid AM/FM mode, is used for simulcast zones, while non-simulcast sites that are part of the same system might use FM (C4FM). A talkgroup isn't going to use one codec on the simulcast zones and a different codec on the non-simulcast sites, because a) that would be impossible, and b) codecs have nothing to do with simulcast!

</rant>

But even with AMBE Vocoders, the X36's still do not even compare to say an APX on an P25 LSM system. Something scanner owners whine about.. I even used to til I realized, a scanner, no matter how good, is not an commercially designed radio specifically designed to handle multiple types of format to professional standards of 2 way comms. If an scanner was, then we would be paying over 2 grand for them. WEG!

Hm. $20 dongles handle LSM just fine. So much for needing expensive hardware.

 

[Medziatkowicz35]

Would changing from Nfm help decode simulcast on 396xt? If so what should I set it on?

 

[Spitfire8520]

Isn't there a new scanner coming out this summer that is supposed to be better at simulcast?

No, there is not.

Would changing from Nfm help decode simulcast on 396xt? If so what should I set it on?

Probably not. I don't think the 396XT offers much in terms of settings for digital decode. The only thing you would probably be able to do is mess with your antenna setup as suggested in the several other forum posts that you have made. There is not anymore anyone can suggest to help fix your reception issues, otherwise this thread would not exist.

Maybe the X36HP series of scanner might work better, but even that is not guaranteed.

 

[Medziatkowicz35]

I'm getting an beam antenna from a friend tomorrow.

 

[MTS2000des]

Hm. $20 dongles handle LSM just fine. So much for needing expensive hardware.

And Unication has a professional receiver that handles LSM for not much more than these cheap plastic garbage pail scanners retail for. While the Unications don't cover all bands, they have superior front ends, are built to IP67 standards and come standard with a 2 year warranty. The scanner manufacturers ship poorly built plastic crap with display backlights and keypads that barely last the 1 year warranties.

The bottom line is the manufacturers are not interested in any advanced technology or quality, they are wanting to milk every last dime out of their decades old tired designs at tremendous profit.

 

[slicerwizard]

The scanner manufacturers ship poorly built plastic crap with display backlights and keypads that barely last the 1 year warranties.

Well, that certainly mirrors my experience. My last Uniden shipped with dim backlighting and a defective audio amp IC and the serial port in my second last Uniden quit working. So much for QC...

 

[WQPW689]

And Unication has a professional receiver that handles LSM for not much more than these cheap plastic garbage pail scanners retail for.

One identifies with your wish for quality. I know I do.

The price points are not nearly the same. There's nothing to be gained by claiming $860 to $895 is the same as 500 bucks.

 

[MTS2000des]

One identifies with your wish for quality. I know I do.

The price points are not nearly the same. There's nothing to be gained by claiming $860 to $895 is the same as 500 bucks.

What will you spend to get some turdy Uniden or Whistler working? Let's see: a $500 scanner, want an extended warranty (if offered by your dealer), that's another $59-79.

Oh then you need some elaborate "Rube Goldberg" Yagi antenna setup just to be able to get a LOCAL system you're well within the intended coverage footprint of.

Average price of a good Yagi is another $69-100, plus good feedline (75 foot of LMR400 with connectors is what, $90-100 bucks), a good mast to mount it on ($35-50), a Polyphaser (unless you don't care about getting hit) $69, what are we up to now (and I'm not even including the labor):

500 + 59 + 69 + 90 +35 + 69= 822 which is not far off from the price of the Unication, which out of the box will receive LSM without all the above reported by posters here required additional antenna system to accomplish the same task.

and the Unication will still outperform the POS scanner anyday of the week. It's rugged, IP67 rated so it won't implode if you're outside and caught in a deluge, and they include a standard 2 year parts/labor warranty out of the gate. No brainer to me.

 

[INDY72]

Would changing from Nfm help decode simulcast on 396xt? If so what should I set it on?

Set the mode to auto, or NFM. Read the "Easier To Read Manuals" to find the multiple ways to adjust digital gain, P25 LP Filter, and other things to help with the issue. Make sure you have the latest firmware 11.01.XXX I believe it is. I am having absolutely 0 issues with my BCD396XT on an P25 LSM system that many others seem to be unable to decode properly. The Indianapolis Dep't. of Public Safety. I also had no issues using an PRO-96 after doing the tiny internal adjustment to the pot screw. I use the RS 800 MHz ducky antenna, and it is performing flawlessly. I go all over Indy, as well as up to nearly 30 miles away in all the surrounding counties, and have no issues whatsoever. I will be taking it on an trip with me to AR in November hopefully, and will then test it on at least 4 other P25 LSM's along my route. I am fairly willing to bet there will be little to 0 issues on any of them.

 

[natedawg1604]

...I am having absolutely 0 issues with my BCD396XT on an P25 LSM system that many others seem to be unable to decode properly. ...

Are you monitoring at the exact same location(s) of the other people reporting decode problems? If not, then it is a meaningless comparison. I would bet you money that where I live (very close to numerous overlapping cells of a simulcast site, where I get massive simulcast distortion on hardware scanners) you would get the same terrible reception with your 396XT that I suffer with my 396XT. Of course, the problems are 100% solved when I use OP-25.

In any event, my point is that users of hardware scanners only have problems with simulcast distortion at certain somewhat random locations, where the coverage from several sites overlaps in a certain manner. Therefore, it is entirely common to have awful simulcast distortion problems with hardware scanners in one location, drive a few miles away and have great reception. I suspect that is what you're experiencing.

Finally, consider you may not even realize you are experiencing simulcast distortion because you are so used to it and basically tune it out: when I first started using OP-25 at my house (where I have awful reception on radio shack and Uniden hardware scanners), I was shocked how clean the audio was without simulcast distortion. I didn't even realize how bad the simulcast distortion was, because I had no point of reference. So without OP-25, SDRTrunk (which also supports simulcast) or a commercial radio, you probably have no way to meaningfully determine how well you're scanner handles simulcast. Your signature indicates you have an APX radio - do have this simulcast site mentioned in your post, programmed in that radio?

 

[INDY72]

Yes the APX is on one of the currently 3 subsystems of the aforementioned TRS. On that subsystem, it sounds better of course, but that is to be expected. On the 396XT, on that same subsystem, it sounds very clear, and crisp in every part of the system's footprint that I have traveled through, even in basements. On another subsystem, the 396XT has some issues, in basements, or fringe areas. My 96, before I killed its 800 MHz P25 ability (broke the pot screw), was doing just as good on the first subsystem, but did have issues on the second in more places. Before doing that adjustment it was an nightmare due to age issues.

 

[bailly2]

paint can antenna. best results i have got. put antenna through hole on side of paint can near bottom.

 

[RFI-EMI-GUY]

(snip)

The LSM problem with scanners can be summarized as this: the output of an FM demodulator is undefined when there is no signal present at the input. That is, when both the in phase (I) and quadrature (Q) components (of the RF/IF signal) are both zero, the signal magnitude is therefore also zero, and thus the FM demod output is undefined. This condition is most evident in Fig 13(A) at the first of the two pages mentioned above...

73

Max

Question 1. If there is intelligence conveyed in the magnitude (AM component), then how do these FM discriminator receivers decode LSM at all? I would think there would be a very high BER continuously regardless of site overlap.

Question 2. Motorola and Harris have different "secret sauce" yet claim their radios operate on each others systems. The P25 specs and tests simply define a delay spread acceptance of >/= 50 usec, with no other digital receiver performance criteria. How can the vendors claim that they meet P25 specs and can inter operate with each other in the spirit of P25?

Question 3. Put another way, how can the end user of Motorola or Harris (or Unication, Tait, BK etc) products be assured the radios will inter operate?

Update: OK I read LSM-101 down to the "cat"! Q1 makes more sense to me. Perhaps the implementation of FM discriminator plays around with clock recovery to optimize data recovery?? And still the questions remain. Q2 and Q3.

 

[slicerwizard]

Harris is "different enough" to avoid patent issues, not different enough to create problems. They both lower the power level while phase shifting and restore it afterward (at the symbol centers)

 

[KA1RBI]

Question 1. If there is intelligence conveyed in the magnitude (AM component), then how do these FM discriminator receivers decode LSM at all? I would think there would be a very high BER continuously regardless of site overlap.

I've seen exactly that, many times - continuous high BER so bad that the scanner can't even detect or lock a P25 signal. The same antenna connected to a receiver running OP25 gives 100% perfect copy....

Also, the FEC helps effectively reduce the BER but only to a limited extent.

Finally, there are many cases in LSM systems where the trouble is not present. Certain conditions have to exist (apparently including that there must be more than one simulcast TX coming in to the receiver)...

Max

 

[KA1RBI]

Question 2. Motorola and Harris have different "secret sauce" yet claim their radios operate on each others systems. The P25 specs and tests simply define a delay spread acceptance of >/= 50 usec, with no other digital receiver performance criteria. How can the vendors claim that they meet P25 specs and can inter operate with each other in the spirit of P25?

These can be addressed one at a time - thanks for posting these excellent questions.

I think this part of Q2 is the key

can inter operate with each other in the spirit of P25

DVSI Products USB-3000™

The enhanced full-rate AMBE+2™ vocoder is fully compatible with the older IMBE™ vocoder that was used in the APCO Project 25 Phase 1

DVSI Evaluation Results

DVSI developed an Enhanced (AMBE+2) P25 vocoder ... available in a 7200 bps Enhanced full-rate vocoder configuration which is fully interoperable with the existing P25 full-rate vocoder standard (TIA-102BABA).

Conclusion so far: These two distinct vocoders are "compatible" and "interoperable" (officially).

However

http://dps.mo.gov/dir/programs/intercomm/docs/Project25.pdf

Project 25 radios operating on MOSWIN must utilize, at a minimum, the IMBE (Baseline) P25 vocoder. However, agencies should strive to utilize the Project 25 Enhanced Full Rate Vocoder (AMBE + 2) as it is available on newer radios from multiple manufacturers and outperforms in all scenarios any previous full or half rate vocoder in areas of noise suppression and voice clarity. The AMBE + 2 vocoder is the preferred Project 25 vocoder for use in the MOSWIN network...

http://www.efjohnson.com/resources/dyn/files/171947z8ebcbe0c/_fn/Vocoder_09_09.pdf
In every test ... the Enhanced Full-Rate (AMBE+2) Vocoder outperformed all other vocoders, including the “baseline” IMBE Vocoder

So, one vocoder "outperforms in all scenarios any previous" vocoder, "including the "baseline" IMBE vocoder", yet the two vocoders have been declared "interoperable" and "compatible" as if by decree,

How can the vendors claim that they meet P25 specs

For many years whatever moto+dvsi did was considered P25 standard, even when it differed from whatever spec(s) happened to be current at the time. A good example of this is LSM - receivers for this modulation format are correctly described only in the P25 Phase II/TDMA specs (differential QPSK receivers) - even though Phase I LSM systems also require this type of receiver. Another example is the vocoder one cited above - the AMBE+2 full rate vocoder is in common use years before its specifics are publicly documented (if they ever are - or are they still considered trade secrets?)....

So, can you be more specific as to what you mean by "to inter operate in the spirit of P25"?

 

[natedawg1604]

I've seen exactly that, many times - continuous high BER so bad that the scanner can't even detect or lock a P25 signal. The same antenna connected to a receiver running OP25 gives 100% perfect copy....

....
Max

Yeah that is exactly right. At my house, the 396XT will regularly lose the CC on a nearby simulcast system, even though the CC frequency doesn't change and even though it's a VERY strong signal with paperclip reception (coming from approx. 3-5 different cells). Like you said, as soon as I run OP-25 connected to the same antenna as my hardware scanner, with the antenna mounted in the exact same location, all simulcast distortion is 100% gone.

 

[RFI-EMI-GUY]

These can be addressed one at a time - thanks for posting these excellent questions.

I think this part of Q2 is the key

(snip)

So, can you be more specific as to what you mean by "to inter operate in the spirit of P25"?

Ok; Yes I understand that DVSI has two compatible vocoders, that is the easy part since they are sole supplier.

-------but what I really meant was, because Motorola and Harris have two very different and proprietary linear simulcast modulations, Motorola CQPSK and Harrisn WCQPSK/HDQPSK how can each vendor build a receiver that will be compatible with each other?

Also important, how does the P25 testing process ensure compatibility?

 

[Boatanchor]

I've seen exactly that, many times - continuous high BER so bad that the scanner can't even detect or lock a P25 signal. The same antenna connected to a receiver running OP25 gives 100% perfect copy....

Also, the FEC helps effectively reduce the BER but only to a limited extent.

Finally, there are many cases in LSM systems where the trouble is not present. Certain conditions have to exist (apparently including that there must be more than one simulcast TX coming in to the receiver)...

Max

My local trunking system is predominantly traditional C4FM. My Uniden and Whistler scanners have no problems monitoring most sites.

However, in this particular system, the network operators have chosen to implement a couple of LSM sites to augment coverage into remote locations. The simulcast sites in question are about 20 miles apart and operate on the same frequencies.

I am a radio technician and while I don't service the trunking equipment at these sites, I do visit them on a regular basis to service other systems.

When I go to these sites with my scanners, neither the Uniden or GRE/Whistler equipment will decode the CC from these particular simulcast bases. I can remove the antenna from the scanner, so that the signal is only half scale and still no decode whatsoever.. Whatever the LSM scheme is being used, the scanners simply will not decode it. And, it has nothing to do with simultaneous reception/interference from the other site, since removing the scanner's antenna makes no difference. In other words, if you were monitoring these sites from a remote location, even using Yagi antennas would not help.