DMR Decoding Errors (DSD+ FastLane)

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tbailey1712

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Hi,

I'm using the binaries from the DSDPlus2p32 package and attempting to decode a nearby DMR repeater.

Starting up with the following, stock cfg files:
C:\DSD> fmp24 -o20001 -P86 -f___.____
C:\DSD> DSDPlus -i20001 -o2 -v2

Using a NooElec RTL-SDR stick under Windows7

I've adjusted the gain up and down, no difference, I get screenfulls of the following error messages. Even if I set it to an open simplex frequency and test it with an HT, I'm not getting any output in the Event Log.

Ideas for what to tweak??


Sync:+DMR
+DMR CACH ERR slot1 BS DATA DCC=5 CSBK
Sync:+DMR
+DMR CACH ERR slot1 BS DATA ERR3 DCC=5 CSBK
Sync:+DMR
+DMR CACH ERR slot1 BS DATA ERR1 DCC=5 CSBK

+DMR CACH ERR slot1
+DMR CACH ERR slot2 BS VC2 e:6r7r6r
 

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MS Voice would indicate you are monitoring a simplex transmission (or maybe the input to the repeater?). If you are trying to test with your own radio in simplex mode make sure you are set to low power and a ways away from your dongle.
 

tbailey1712

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I can see in the console window a TCP error and something about closing an existing connection. Do you get this error all the time?
That was due to starting/stopping DSDPlus in the other window to change some settings.


Your event window indicates that you are trying to receive DCDM "Dual Capacity Direct Mode" this is a simplex mode and no repeater involved.

Here is a short video about it:
Dual Capacity Direct Mode Overview & Configuration Video

Cheers.
That seems about right, it's the frequency for my office building's operations. They are licensed for a repeater pair, but have only ever picked up traffic on this frequency.

Not sure about the video link...looks like that's for how to program the radio with CPS. I'm more interested in how I get DSDPlus to decode the voice data.
 

thewraith2008

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Sorry the video link was only for info about DCDM and that it's not using a repeater, I should have clarified.

"e:5r726r " I see this error when the gain is set wrong, but you said you tried that.
The other thing to check, is that the signal polarity is not on. In the event window press "P" should see "NOT inverting signal polarity" or "Inverting signal polarity"

Cheers
 

slicerwizard

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The signal from your radio is much too strong. Try dropping the gain to zero and move to another room when testing. Also, since you're dealing with simplex signals, add -fr to the DSD+ command line to lock the baud rate.
 

tbailey1712

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Hi everyone - I'm still seeing identical errors on the simplex monitoring. If I put in a local Amateur DMR repeater, this is what I see. Screen fulls of CACH ERR slot1 and nothing in the event window.
 

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natedawg1604

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Hi everyone - I'm still seeing identical errors on the simplex monitoring. If I put in a local Amateur DMR repeater, this is what I see. Screen fulls of CACH ERR slot1 and nothing in the event window.
The event window is only active during voice grants. The screenshot shows an idle data burst message, which is often broadcast at periodic intervals on DMR repeaters.

Also, what type of antenna setup are you using? Have you tried re-adjusting antenna placement to reduce errors?
 

tbailey1712

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I have a mini mag mount that is able to pull in analog voice just fine in the same band.

Guess I should have been a little more descriptive of that last screen shot. That was a grab during an active QSO on TS1 of a DMR repeater about 2 miles from my location. S9 on the portable and you can see a pretty solid signal on the SDR as well even with the gain turned down.

I was listening to the voice conversation perfectly well on my HT and did a screen grab. Nothing was coming through on the SDR though except screenfulls of CACH ERR.
 

slicerwizard

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You're not centered on the signal. Try turning off auto-centering in FMP24 and manually center it if required. You (and the rest of us) have to pay attention to the fine details...
 

thewraith2008

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Also noticed that in each screenshot your PPM is different. This value should be determined and then left.
The last shot shows that the AFC has to go 1510Hz to find signal. As slicerwizard said you need to center that on the correct frequency. I know you have a cheap dongle but it should stabilize after about 10-15min of use. Calibrate it then.

I find a good (enough) calibration source is the ATIS at your local airport. My ATIS is only out a few Hz.
 

tbailey1712

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Also noticed that in each screenshot your PPM is different. This value should be determined and then left.
Well, I actually switched dongles wondering if that might be the problem. Tried an identical NooElec but no improvement.

The last shot shows that the AFC has to go 1510Hz to find signal. As slicerwizard said you need to center that on the correct frequency. I know you have a cheap dongle but it should stabilize after about 10-15min of use. Calibrate it then.

I find a good (enough) calibration source is the ATIS at your local airport. My ATIS is only out a few Hz.
I've been calibrating against NWS on VHF and one of the busier Chicago Police analog frequencies on UHF and have it pretty darn close.

Is that what you're referencing by centering, making sure the PPM is spot on?
 

thewraith2008

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The frequency for NSRC is 441.21875 as you have, but the green line peak is not centered on the light green bandwidth field. It's not out much but for some reason FMP24 has also applied 1510Hz of frequency correction on top of that. Either the repeater is off frequency or the PPM is out.

The NWS should a good calibration source you'd thing. They probably use a rubidium or caesium standard. If your dongle can get WWV on 10MHz that's supposed to be spot on too using the above standards.

You did try the signal polarity as mentioned above?
 

slicerwizard

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If your dongle can get WWV on 10MHz that's supposed to be spot on too using the above standards.
And his 87 PPM error will translate to a whopping 870 Hz. Each 1 PPM adjustment he'd make would yield a 10 Hz shift, which a) the dongles can't do (tuning granularity is much higher), and b) a 10 Hz shift would be undetectable in the spectrum display.

PPM adjustments have to be done using high frequency references, preferably control channels in the 770, 860 or 935 MHz bands.
 

thewraith2008

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Using 10Mhz has never been a issue for frequency counters and other instruments that measure/generate into the GHz range. They even use 10MHz rubidium standard in GSM towers @ 900MHz.

I get the same result if I set my PPM to 10MHz from WWV or use the FCCH offset @ 67708hz from base frequency of a GSM tower. All comes down to source accuracy and GSM and WWV are PPB in that area.
 
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