How to Identify Digital Phone Modes on VHF/UHF

David Witkowski, W6DTW Revision 1.2

Purpose

 Provide recorded audio of various digital systems so that hams without digital gear can identify (in some cases) modes they might hear on VHF/UHF bands   Show spectra of various digital systems Covers:     D*Star APCO Project 25 Phase 1 (aka “P25”) NXDN™ DMR Tier 2 (functionally akin to MotoTRBO ™) – uplink (mobile)

Methodology

 Equipment:   Anritsu S412E LMR Master™ for signal generation and spectrum analysis Kenwood TS-2000 w/ Ham Radio Deluxe’s “Audio Grabber” for audio recordings   FM Mode, 5 KHz deviation D*Star was K6MDD (147.475, Mt. Diablo) recorded off the air from CM97  P25, NXDN, and DMR were generated by the S412E, cabled to the TS-2000 through an attenuator

K6MDD D*Star

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Digital Smart Technologies for Amateur Radio

”   JARL, ICOM Modulation: GMSK impressed on FM modulator  Ref: K6WX “FM Spacing Requirement for Amateur Transceivers”

D*Star Sound Sample (Click to play)

K6MDD D*Star Spectrum

APCO Project 25 Phase 1

   Aka “P25” - Federal standard for encryption & interoperability Some amateur use in SF Bay Area Modulation: Continuous 4-level FM, 9600 bps (4800 baud, 2 bits/symbol), 12.5 kHz channel

P25 Sound Sample (Click to play)

APCO Project 25 P1 Spectrum

NXDN

 ICOM/Kenwood response to P25  Modulation: 4-level FSK, 9600 bps, 12.5 kHz bandwidth  In audio, almost perfectly identical to P25

NXDN Sound Sample (Click to play)

NXDN Spectrum

ETSI DMR Tier 2 (Simplex)

   Uplink (HT to Base) uses 2-slot TDMA in a 12.5 kHz bandwidth Downlink does not pulse Note how in simplex the spectrogram appears to “pulse”, audio has “machine gun” sound

DMR Simplex Sound Sample (Click to play)

ETSI DMR Tier 2 Simplex (Spectrogram)

ETSI DMR Tier 2 (Repeater)

  Sound is a constant “churning” versus the “sputtering” in simplex  Differs from the simplex signal, both timeslots used Note that bandwidth is still 12.5 kHz

DMR Repeater Sound Sample (Click to play)

ETSI DMR Tier 2 (Repeater Spectrum)

Comments

   P25 and NXDN are almost impossible to distinguish with spectrum or audio  No known NXDN amateur systems – yet D*Star easy to identify – you can hear a brief “beep” of 2400 Hz audio before data MotoTRBO simplex easy to identify – has a pulsed sound (because it’s a TDMA mode) – sounds like a “machine gun” or “helicopter”  MotoTRBO Base/Repeater has a constant “grinding noise” more like P25 or NXDN

Overview

 As of March 2011 several digital voice mode repeaters have appeared on the SF Bay Area VHF/UHF bands  D*Star   P25 MotoTRBO (variant of ETSI DMR Tier 2)  There has been some confusion about this; people hearing digital audio on their analog FM rigs have erroneously blamed “noisy” or “splattering” D*Star systems

Change Log

  Version 1.0 (unmarked)  Initial posting 27-March-2011  Contains P25 Phase 1, NXDN, D*Star Voice, and MotoTRBO MS (“Mobile Station”) on simplex Version 1.1

 Posted 28-March-2011  Adds MotoTRBO BS (“Base/Rptr Station”) using O.153 “PN9” and TSCC patterns

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