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

[slicerwizard]

I don't know if DSDPlus recommends this, but I specifically run -f1 -mp (force Phase 1, use PSK optimization). If you use -mp, don't try to decode a non-simulcast P25 Phase 1 system though because you won't be able to [and dsdplus -h tells you so].

I just disabled -mp on mine, and I can't tell if there is much of a difference or not. But I'd try "-f1 -mp" specifically for P25 Phase 1 simulcast systems and see if improves any more than it already has for you.

I would suggest that you use "b" in your FMP to toggle between the bandwidths, but I think if you lock in -f1 -mp (or if LSM is detected automatically), you can't adjust bandwidth anyway because I believe the whole package specifically fine tunes everything when a simulcast sig is detected. Could be wrong.

-f1 -mp is worth a try though. It may not do anything as -mp may already be in use once simulcast is detected.

Mike

The 2.5 change log says:

when a TCP link from FMP24 or FMPA is used and P25 PSK modulation is detected,

FMP24/FMPA and DSD+ stop using FM demodulation

DSD+ generates a pseudo-C4FM audio waveform and
displays it in the source audio waveform window

the pseudo-C4FM audio waveform can be recorded by pressing 'R' in DSD+

no advanced decoder options are required for best decoding of P25 PSK signals

these options (-mp, -dr<num>, -dh<num>, -ds<num>, -dd<num>, -dv<num>)
will have no effect on PSK decoding when TCP linking is used

if you also monitor another signal type (NXDN, DMR, C4FM P25, ...),
use advanced decoder options that benefit *that* signal type

double my rtl?

He's saying you'd have to spend twice as much to get fast delivery. Bear in mind that Amazon's delivery estimates are quite pessimistic - goods will often arrive in a few days.

Well, FWIW, my cheap RTLs also decode conventional VHF digital frequencies. I know there are better receivers, but, when you consider price, these little things are hard to beat.

Gah. It's not the dongles - it's the dinky antennas on the dongles you recommended that won't perform well on VHF.

I think the modulation used by simulcast systems is slightly different than the H-DQPSk used for TDMA downlink. However, if they bought phase two capable equipment with linear amplifiers, I suppose that might be reason to use CQPSK instead of C4FM.

Sorry, not following you. Reason to use CQPSK instead of C4FM for what?

 

[AggieCon]

Sorry, not following you. Reason to use CQPSK instead of C4FM for what?

For Phase 1 downlink. Kind of a "because we can, we will" (since, if their repeaters are Phase 2 compatible, they will have linear amplifiers). I'm, of course, just speculating. I have no clue about the systems you reference. I also am not aware of any advantage of CQPSK over C4FM for single site P25 Phase 1 digital.

But also, this seems to question DSD+ inherently supporting the LSM-CQPSK modulation scheme:

when a TCP link from FMP24 or FMPA is used and P25 PSK modulation is detected,

FMP24/FMPA and DSD+ stop using FM demodulation

DSD+ generates a pseudo-C4FM audio waveform and
displays it in the source audio waveform window

the pseudo-C4FM audio waveform can be recorded by pressing 'R' in DSD+

Is it saying it switches to PSK when simulcast P25 is detected, and FM C4FM when "regular" P25 Phase 1 digital is used? Or is the described method for all P25 Phase 1 digital traffic?

Yea, those short RTL aren't going to allow you any gain, lol. But for $10 on a receiver, surely one has enough in their budget to make or buy an appropriate antenna.

 

[slicerwizard]

For Phase 1 downlink. Kind of a "because we can, we will" (since, if their repeaters are Phase 2 compatible, they will have linear amplifiers).

So switch between C4FM and CQPSK for Phase I and Phase II calls? What benefit would that complication yield?

I'm, of course, just speculating. I have no clue about the systems you reference. I also am not aware of any advantage of CQPSK over C4FM for single site P25 Phase 1 digital.

Well, it's a huge advantage for DSD+. 2.10 pulls in weak CQPSK sites far better than it does C4FM. The decoding on weak RCMP (C4FM) control channels is definitely poorer than any similar-strength CQPSK CC. No idea if real radios see an improvement, but I wouldn't be surprised, as CQPSK encodes more timing information than C4FM.

But also, this seems to question DSD+ inherently supporting the LSM-CQPSK modulation scheme:

Is it saying it switches to PSK when simulcast P25 is detected, and FM C4FM when "regular" P25 Phase 1 digital is used? Or is the described method for all P25 Phase 1 digital traffic?

It says when P25 PSK modulation is detected. How do you get from there to "for all P25 Phase 1 digital traffic"?

Yea, those short RTL aren't going to allow you any gain, lol. But for $10 on a receiver, surely one has enough in their budget to make or buy an appropriate antenna.

And then you have to deal with that stupid MCX connector.

 

[KevinC]

And so we're on all the correct page...Phase 2 TDMA uses H-DQPSK. Doesn't matter if it's single site or simulcast.

Now, back to your regular discussion...

 

[AggieCon]

Well, I tried it on every simulcast system/zone around here. That's about 15 separate zones. It includes a couple of non-simulcast zones that are using CQPSK, no doubt to handle Phase II talkgroups.

You referenced non-simulcast systems running CQPSK. I am not aware of the benefit of this; hence, perhaps just because they can?

So switch between C4FM and CQPSK for Phase I and Phase II calls? What benefit would that complication yield?

I'm pretty sure Phase I digital is always modulated differently than Phase II TMDA. C4FM or CQPSK for Phase 1 digital and H-DQPSK for Phase 2 TDMA. To make it even more interesting, the Phase 2 TDMA uplink is an additional modulation, H-CPM, which does not require linear amplification (save portable's battery life).

Repeaters can have more efficient amplifiers if using only C4FM. CQPSK and H-DQPSK equipment require linear amplifiers.

And so we're on all the correct page...Phase 2 TDMA uses H-DQPSK. Doesn't matter if it's single site or simulcast.

 

[KevinC]

I'm pretty sure Phase I digital is always modulated differently than Phase II TMDA. C4FM or CQPSK for Phase 1 digital and H-DQPSK for Phase 2 TDMA..

Correct.

 

[mtindor]

The 2.5 change log says:

when a TCP link from FMP24 or FMPA is used and P25 PSK modulation is detected,

FMP24/FMPA and DSD+ stop using FM demodulation

DSD+ generates a pseudo-C4FM audio waveform and
displays it in the source audio waveform window

the pseudo-C4FM audio waveform can be recorded by pressing 'R' in DSD+

no advanced decoder options are required for best decoding of P25 PSK signals

these options (-mp, -dr<num>, -dh<num>, -ds<num>, -dd<num>, -dv<num>)
will have no effect on PSK decoding when TCP linking is used

if you also monitor another signal type (NXDN, DMR, C4FM P25, ...),
use advanced decoder options that benefit *that* signal type

I knew I read that. I just didn't feel like re-reading it I get it. If you wan't to monitor LSM / CQPSK whatevver the hell you want to call it, then just use it. Don't add any advanced decoder options. That's good. I'll remove them from my batchfile, ,which will make life easier when I want to change freq with FMPA|24 on the fly and go from an LSM site to a C4FM site, or to a DMR/NXDN site.

RIF -- Reading is Fundamental. I remember the commercials from my childhood. I just dont' heed them.

M

 

[natedawg1604]

Just FYI, tonight I made raw source audio recordings from CC & VC instances of DSD+ 2.10 re: my local simulcast system discussed above (not sure if I need to post raw files from both instances for debug purposes?).

Raw source audio file re: CC Instance of DSD+ 2.10 on Local Simulcast System

Raw source audio file re: VC Instance of DSD+ 2.10 on Local Simulcast System.


As you will see, I am getting a bunch of error messages in the VC & CC terminals, and I can't figure out how to make them go away. Among other things, I'm somewhat regularly seeing ENC flags in the event log for non-encrypted talkgroups, presumably a sign of bad decoding.

As noted in my earlier post, I get paperclip reception of this system from my location (and I'm using Larsen Tri-band antennas). With OP-25, as soon I fire up scope.py it just starts decoding this system without any problems, and it stays running for days or even weeks. Likewise, with OP-25 I never have to screw around with antenna placement, presumably because the reception is so good. Therefore, I'm pretty befuddled as to why I'm having so many problems reliably decoding this simulcast system on DSD+.

Any suggestions on how I could improve decoding on this system with DSD+ would be much appreciated...

 

[mtindor]

Nate,

This question has probably already been asked/answered, but what do you use for input?

Are you using strictly FMPA|24 for CC/VC audio input along with TCP/IP linking? Or are you using some other signal input for one/both?

Mike

 

[natedawg1604]

Nate,

This question has probably already been asked/answered, but what do you use for input?

Are you using strictly FMPA|24 for CC/VC audio input along with TCP/IP linking? Or are you using some other signal input for one/both?

Mike

FMP24 (2 instances) with TCP linking to the VC & CC instances of DSD+ 2.10.

 

[slicerwizard]

You referenced non-simulcast systems running CQPSK. I am not aware of the benefit of this; hence, perhaps just because they can?

They have linear amps for the Phase II traffic. That gives them the ability to run a linear mode (CQPSK) for Phase I traffic. The fact that they're doing it suggests that there may be a benefit for system radios. As I said, it's definitely benefiting DSD+, which is fine by me!

To make it even more interesting, the Phase 2 TDMA uplink is an additional modulation, H-CPM, which does not require linear amplification (save portable's battery life).

Not surprising, since inbound traffic is not simulcast. Going to a more complex/refined modulation mode (compared to C4FM) makes sense, since Phase II pushes 25% more bits over the air compared to Phase I.

Any suggestions on how I could improve decoding on this system with DSD+ would be much appreciated...

Contact the developers. Doesn't sound like we can do much for you.

 

[natedawg1604]

....

Contact the developers. Doesn't sound like we can do much for you.

How? Can you post or PM an Email?

 

[mtindor]

How? Can you post or PM an Email?

Look in your DSDPLus TXT file. Should be in there, at the bottom. Should be the same email address that sends you your Fast Lane.

Mike

 

[AggieCon]

(CQPSK) for Phase I traffic. The fact that they're doing it suggests that there may be a benefit for system radios. As I said, it's definitely benefiting DSD+, which is fine by me!

So the new DSD+ handles CQPSK better than C4FM? Is that the point?

 

[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

I keep coming back to this comment and it jars my memory regarding Motorola's early ASTRO simulcast systems. Motorola used a technique which they called "wide pulse" in order to improve the symbol recognition at the receiver. It was also used for simulcast Securenet (FRED). There were questions outside the company as to whether this technique would meet some of the narrower emission masks.

Could it be that the zero magnitude component of LSM is not for the conveyance of information (though it could improve clock recovery), but serves to blank modulation energy which would normally exceed the modulation mask and would be destructive at the limits of the simulcast delay differential?

What I am picturing is wide pulse C4FM with sharp attenuation at the transition between symbols.

It is late and I am probably pondering in an area beyond my expertise.

 

[jukes]

as far as my radio experience that goes back to age 7 with my Father I'm now 60 the 436/536 and the HP-2 are by far the worst yes folks the worst Uniden performing scanners I have ever owned the NJCIS system is terrible and I know there are a lot of users that feel the same way. Not going to go deep into it because I do know radios and these mentioned radios are terrible. Guess that's why uniden and whistler are going /trying to put out new radios to address these problems with them............ this time I am going to wait at least a year to see if these new and better radios will decode as they say they will so with that I will hold on to my $500 plus dollars this time sell the other 3 radios if I can in order to buy one that hopefully works as advertised................. and for the record the above mentioned radios are yes they are programmed correctly.

 

[AggieCon]

Hi Jukes, the reason Whistler is putting out a "new" radio is to sell more radios and make more money. Their goal isn't to provide us what we need. Their goal is to make money by getting us to buy more radios. The new radio will not solve the simulcast problem. Read this post for more background: http://forums.radioreference.com/2584582-post94.html

 

[natedawg1604]

.... this time I am going to wait at least a year to see if these new and better radios will decode as they say they will....

I hate to beat a dead horse, but as was mentioned previously in this thread, no scanner manufacturer has ever claimed to specifically support Simulcast. You should look at the new Unication G4/G5, which are a bit more expensive but do support simulcast.

 

[Medziatkowicz35]

how much are the unication g4/g5? Are we talking like dell computer expensive or like emachines computer expensive?

 

[AggieCon]

how much are the unication g4/g5? Are we talking like dell computer expensive or like emachines computer expensive?

Probably closer to $1,000 from what i can tell. So like a Thinkpad.