TB7100 RB-STM32-DVM Troubles

1. Audio Signal Properties
2. Timeline of tests
3. mmdvmcal Results
4. csbk - Controll Signaling Block
5. G4KLX Wiki Notes
6. MMDVM Specification
7. DMR Audio RX Images
8. SK2HG - Kalix Radio Club

1. TB7100 Repeater
2. TB7100 Config for the RB-STM32-DVM
3. TB7100 RB-STM32-DVM Build

The TROUBLE is that the RB-STM32-DVM refuses to decode the RX Audio form the TB7100 repeater. Why?

What can affect the RX Decoding of the DVM?

• Amplitude (mV)
  The STM32-DVM will saturate the MMDVM ADC input at signals much stronger than -30dBm.
  Too low and ADC will fail on weaker signals
• Frequency offset (Hz)
• Phase shift or Signal Delay - This is the most difficult to get correct
  1 mSec per 25 DMRDelay
  Each signal frame is about 3.5 mSec or 87.5 DMRDelay
• DC Offset (mV)
• Signal invert (logical)

Audio Signal Properties

• Channel spacing: 12.5 kHz
• TDMA: Two slots using time division
• RF modulation: 4FSK
• Symbol rate: 4800 symbols per second
• Symbol time: 1/4800 = 208μS (milli seconds)
• FSK frequencies: +1944, +648, -648, -1944 Hz

Timeline of tests

1. 2020-01-31 - Analyse mmdvmcal results
2. 2020-01-31 - run more mmdvm cal tests
3. 2020-02-02 - Understand SAM ADC conversion on RX chain.
4. What should I see on TP1, TP2, TP3
5. Look at specs of MCP6002

mmdvmcal Results

• BER - Bit Error Rate
• FEC - Forward Error Correction
• DVM - Digital Voice Modem
• DMO - Direct Mode Operation

csbk - Controll Signaling Block

If its derives, check to TCXO output with a scope. The sinus level must be 0-3.3V. If the 0 is not reach (highest value), you may shorcut C22.

G4KLX Wiki Notes

MMDVM Specification

DMR Audio RX Images

SK2HG - Kalix Radio Club

Kalix Radioklubb C/O Sture Bylund Kajvägen 5 952 95 BÅTSKÄRSNÄS Sweden Page managed by SM2OAN

Adjusting the RX settings was much more diffcult, I did not found any info about how the MMDVM.ini file should look like for TB7100. The TB7100 has DSPs in both the TX and RX path so the signals are delayed. This was no problem with my first DMR project, the GM-340 based Repeater.

Before struggeling with the RX path I decide to open the Squelch as the Audio output was squelched. It had to be done with the Tait calibration program (TB71_CAL) not with the normal CPS program (TB71_XPA), by setting a low value for squelch opening, I think I put -136 dBm there. After a lot of trying I found the settings below to work. I have used them for both repeaters with very good result.