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Ham VHF/UHF Digital Voice Modes

For the beginner

Reminder about some terms from the 1st presentation on HF digital modes

• When looking at the “digital modes” of today, you have to look at it from two perspectives

– Encoding (how 1’s and 0’s are encoded onto the carrier wave)

– Frame Format (how the data is formatted to mean something)

• One character at a time or

• A group of characters “packed” together as one unit

Summary of Encoding Techniques (from HF Digital Modes Presentation)

• On/Off Keying; dots/dashes

• AM/FM/SSB (no frame format since there’re no 1’s and 0’s)

• FSK/MFSK (Frequency Shift Keying or Multiple Frequency Shift Keying)

• PSK (Phase Shift Keying) (Binary and Quadrature)

• PTCM (Pragmatic Trellis Coded Modulation)

• PSM (Phase Shift Modulation) (Modulating the phase of the carrier wave with the signal)

*Some sound “diddly”; some sound “chirpy”; some sound “musical” on HF *At VHF, higher data rates are allowed, so they begin to sound like “static”, “screechy”, or “scratchy”

Summary of Frame Formats (from HF Digital Modes Presentation)

• Single Character – Morse Code – 5-bit Baudot – 6, 7 or 8-bit ASCII (with or without Huffman compression at this layer,

error correction code) – Varicode (with or without Huffman compression at this layer, error

correction code) – Base128

• Grouped Characters

– APRS protocol

• State Oriented (as apposed to request/response)

– WinLink

Summary of HF digital modes

• Four categories (I’ve broken them down into) – Single character, keyboard to keyboard modes

• RTTY, PSK31, PACTOR, THROB, OLIVIA, JT6M, DOMINO, THOR, JT65, G-TOR, FT8, etc, etc, etc…

– Images • SSTV, Hellschreiber

– Computer processed, Grouped sets of characters sent, then processed by a computer at the receiving end and displayed accordingly • APRS, CLOVER

– Some that don’t really fit the above categories • WSPR, ROS, WinLink

Now, the Digital Voice Modes (mostly associated with VHF/UHF)

• EchoLink • IRLP • D-Star (Icom) • System Fusion (Yaesu) • P25 • NXDN (Icom & Kenwood) • DMR (several Chinese manufacturers, Kenwood) • A few words on “trunked” radio systems

• First, before there was digital, there was analog

147.94 Mhz In 147.34 Mhz Out

Transmits on 147.94 Mhz Hears on 147.34 Mhz

By the way, I’m not turning on my transmitter unless I hear a 136.5 hz tone

Frequency Modulation

-20Khz -15Khz -10Khz -5Khz 0 +5Khz +10Khz +15Khz +20Khz

Frequency Modulation = Amplitude of your voice causes Frequency Deviation

-20Khz -15Khz -10Khz -5Khz 0 +5Khz +10Khz +15Khz +20Khz

Generally speaking, 15Khz of deviation is normal, which means, in practice 20Khz of BW used

Purpose of going Digital?

• 1912, conserve bandwidth (Radio Act of 1912)

• 1930’s, conserve bandwidth (Single Side Band)

• Today? Digital? –Conserve bandwidth

• Next question, how to digitize your voice…

How to turn your analog voice into a digital bit stream

• LOTS of A/D and D/A converter algorithms specifically designed for converting voice into digital (VOCODER) – LPC-10, 2400 bit/s, linear predictive coding – Code-excited linear prediction (CELP), 2400 and 4800 bit/s (STU-III) – Continuously variable slope delta modulation (CVSD), 16 kbit/s – Mixed-excitation linear prediction (MELP), (FNBDT) – Adaptive Differential Pulse Code Modulation (ADPCM) (STE) – Algebraic code-excited linear prediction (ACELP 4.7 kbit/s – 24 kbit/s) – Mixed-excitation linear prediction (MELPe 2400, 1200 and 600 bit/s) – Multi-band excitation (AMBE 2000 bit/s – 9600 bit/s) – Sinusoidal-Pulsed Representation (SPR 600 bit/s – 4800 bit/s) – Robust Advanced Low-complexity Waveform Interpolation (RALCWI 2050bit/s,

2400bit/s and 2750bit/s) – Tri-Wave Excited Linear Prediction (TWELP 600 bit/s – 9600 bit/s) – Noise Robust Vocoder (NRV 300 bit/s and 800 bit/s)

A/D and D/A conversion

-Since it’s now a digital signal, degraded signals can be fixed with FEC -Can also be compressed for even less bandwidth 11

EchoLink (a VoIP Ham Protocol)

2 Meter Repeater

Internet

PC PC

Mic Headphones

“CQ CQ… Anybody on this repeater?”

EchoLink

• A Voice Over IP (VoIP) system – EchoLink uses standard H.323

• You can log into the EchoLink system (echolink.org), and then attach to any repeater system associated with EchoLink – Must first create an account at echolink.org by providing

proof you’re a licensed amateur radio operator

• Once you’re connected to a repeater, you’re 59 into the repeater!

• Or, you can connect two PCs and talk to each other

ITU-T standard H.323

• Includes many protocols • The standards most relevant to EchoLink are the audio codecs

(coder/decoders) (These are the A/D and D/A converters using a variety of algorithms) – G.711 (64 Kbits/S) – G.729 (8 Kbits/S) – G.723.1 (5.3 or 6.3 Kbits/S) – G.726 (16, 24, 32 an 40 Kbits/S) – G.722 (48, 56, 64 Kbits/S) – G.728 (16 Kbits/S) – Speex (Audio Compression algorithm) – AAC-LD (Audio Compression algorithm)

• Usually, some sort of hand shaking occurs at initial connection establishment to determine the best codec to use

EchoLink

• Encoding: Voice to Digital conversion through the use of one of many H.323 codecs

• Frame Format: the “IP Packet”

• Authenticated connection, followed by Voice over IP (VoIP)

“IP Packet” International Standards Organization Open System Interconnect Model

7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data 1. Physical

Application, software, program, “app” “programmer’s choice!”

MAC MAC

IP

TCP MTU

“The Wire” or “Radio” or “Fiber Optic”

“TCP or UDP Segment”

“IP Packet”

“MAC Frame”

IRLP

• Internet Radio Linking Project

• Another VoIP protocol

• Main purpose is to link repeaters

• (Freedom Link is not IRLP, they’re linked via RF point-to-point connections using … 70cm links in many instances, I think…)

D-Star (Icom)

• “Digital Smart Technologies for Amateur Radio” – The first digital voice and data protocol designated for amateur

radio – Objective: use less bandwidth

• Encoding: AMBE vocoder (AKA codec) (closed source) – Used by Inmarsat, Iridium and some XM Sat Radio channels – Gaussian Minimum Shift Keying (GMSK) modulated carrier

• Frame Format: D-STAR Digital Voice protocol standard (DV) – 3.6 Kbits/S followed by 1.2 Kbits/S of FEC – On-Air DV rate is 4.8 Kbits/S

• Can link repeaters over the internet • Kenwood and Flex make compatible radios

D-Star (Icom)

D-Star (Icom) • www.dstarinfo.com

D-Star

• 1st, you must register your call sign, otherwise, you’ll be limited to the local repeater – Generally, find the person who maintains the local D-Star

repeater and ask nicely – You must only be registered by the operator of a single

repeater

• Then, program your radio – Can do it from the front panel, but it’s easier to use a

computer program – Four parameters: MYCALL, URCALL, RPT1, and RPT2 – Then set mode (“DV”) and frequency/repeater offset

• Next slide…

D-Star

• MYCALL – your own call sign. You can add “/” and other characters like /P or /M or /7 or /BOB or /92 (for IC-92AD)

• URCALL – can hold routing info or linking commands; to use your local repeater, just set it to “CQCQCQ”

• RPT1 – should be set to your local repeater – This setting doesn’t matter for simplex

• RPT2 – designates where you want your signal to be routed; normally it’s set to your local repeater followed by “<space> G” – <space> G = “Gateway” – This setting doesn’t matter for simplex

• www.dstarinfo.com/dstar-web-calculator.aspx – Can tell you what to put in these fields based on what you want to

connect to

• Next slide…

http://www.dstarinfo.com/dstar-web-calculator.aspx





D-Star

• “module”, “port”, “node” are synonymous

– “A” (module/port/node) = 1.2 Ghz

– “B” (module/port/node) = 440 Mhz

– “C” (module/port/node) = 144 Mhz

• Call Sign Routing

– Next couple of slides

D-Star Call Sign Routing

• Using local repeater (no routing)

• N5VGQ just wants to talk to other local hams using his local repeater K5LET, which is on 440 Mhz (node B), using local repeater K5LET as the Gateway – MYCALL: N5VGQ

– URCALL: CQCQCQ

– RPT1: K5LET B

– RPT2: K5LET G


• Routing to specific repeater and node

• N5VGQ is using his local repeater K5LET and wants to route his transmissions to the B node of the JP1YDS repeater in Japan

– MYCALL: N5VGQ

– URCALL: /JP1YDSB

– RPT1: K5LET B

– RPT2: K5LET G


• Routing to specific repeater and node last used by a specific ham

• N5VGQ is using his local repeater K5LET, and WB5UAA is on vacation somewhere in the world; N5VGQ wants to route his transmissions to what ever repeater WB5UAA used most recently (in hopes of finding/talking to him) – MYCALL: N5VGQ – URCALL: WB5UAA – RPT1: K5LET B – RPT2: K5LET G

D-Star Linking to another repeater

• N5VGQ wants to link his local repeater K5LET to the “B” module of repeater W5ETX in Tyler

– MYCALL: N5VGQ

– URCALL: W5ETXBL

– RPT1: K5LET B

– RPT2: K5LET G

D-Star Linking to another repeater

• N5VGQ wants to link his local repeater K5LET to Reflector 14C, to which many other West Coast repeaters are already linked

– MYCALL: N5VGQ

– URCALL: REF014CL

– RPT1: K5LET B

– RPT2: K5LET G

http://www.dstarinfo.com/reflectors.aspx

D-Star UNLINKING a linked repeater

• N5VGQ wants to unlink his local repeater K5LET from the reflector or other repeater it’s currently linked to – MYCALL: N5VGQ

– URCALL: <space><space><space><space>><space><space><space>U

– RPT1: K5LET B

– RPT2: K5LET G

• Key the radio for about a second and you should get a recording played back saying “remote system unlinked”

D-Star Echo Test

• N5VGQ wants to hear how he sounds on his local D-Star repeater (Echo test)

– MYCALL: N5VGQ

– URCALL: K5LET E

– RPT1: K5LET B

– RPT2: K5LET G

D-Star Information Message

• N5VGQ wants to find out how his local repeater K5LET is currently linked (Information)

– MYCALL: N5VGQ

– URCALL: K5LET I (letter “eye”)

– RPT1: K5LET B

– RPT1: K5LET G

D-Star – DV Dongles, DVAPs, Hotspots

• DV Dongle – Little plastic thing that plugs into your computer USB port – You can then use your computer’s headsets and microphone to connect to a

repeater or reflector

• DVAP – Plugs into your computer like a DV Dongle, but has a small antenna on it – Instead of using computer headsets/microphone, you use your D-Star radio to

talk to the DVAP using DV simplex – Range is limited, but you use your D-Star radio to connect to a repeater or

reflector through your computer

• D-Star Hotspot – Like a homemade DVAP made using FM radio with a data port, a GMSK

adapter board and a computer – Can be used by your D-Star radio to connect to a D-Star repeater if you’re

radio’s not in range of a D-Star repeater

System Fusion (Yaesu)

• Yaesu’s implementation of Digital Amateur Radio • Encoding: AMBE vocoder (AKA codec) (closed

source) for Voice to Digital conversion – C4FM (4-level FSK) modulated carrier

• Frame Format: 960 bits, divided into 5 logical slots

• Wide-coverage Internet Repeater Enhancement System (WIRES-X) is a protocol to link repeaters using VoIP and the Internet

System Fusion (Yaesu)

Wires-X Screen (Provides a little bit of insight)

Connect to a Fusion Repeater

• Specific step-by-step button pushing instructions for all Yaesu Fusion radios

• Generally: – Connect to a local node (for example)

• MIWIZ-FUSION

• AMERICA-LINK

• WORLD-LINK

• CQ AMERICA

– You can then connect to a room • Can search by name

• Can connect by DTMF ID

System Fusion Nodes

• https://www.yaesu.com

System Fusion Rooms

• https://www.yaesu.com

DTMF ID

Project 25 (P25)

• Initiated collaboratively by North American public safety agencies (shortly after September 11, 2001) to address interoperability among emergency communications systems, especially among first responders (city, county, state, federal)

• Standard: Telecommunications Industry Association (TIA), TIA-102 series, which includes 49 separate parts on LMR and TDMA implementations, including trunked radio systems and the following encryption standards: DES, 3DES, AES, RC4 – TIA-102 is the American version of ETSI TS-102… more later…

• (continued next slide)

Project 25 (P25) (continued)

• Planned Time line:

• Phase 1 - IMBE vocoder, C4FM encoding (a special type of 4FSK), single 12.5 Kbps channel (FDMA), and a frame format consisting of 4.4Kbps of IMBE voice, 2.8Kbs of FEC and 2.4Kbs of signaling and control for a total of 9.6Kbs of total channel throughput

• Phase 2 - AMBE+2 vocoder, two TDMA channels (6.25Kbs X 2), a frame format which requires only 6Kbs (including FEC and signaling) per channel, and a goal to be backwards compatibility to Analog FM and Phase 1

• Future phases still to be determined. TIA was collaborating with the European Telecommunications Standards Institute (ETSI) but stopped in 2010.

NXDN

• Encoding: AMBE2+ vocoder, 4FSK • Frame Format: FDMA, 12.5Kbs or 6.25Kbs

– Can be voice/voice, voice/data, data/voice, data/data – Supports a bit stream encryption, and two block

encryptions: DES and AES

• Developed jointly by Icom and Kenwood and accepted at an ITU-R meeting (Study Group 5) in November of 2016 – Spin off from P25?

• Standards also includes Trunking • Several other vendors: Motorola, Vertex, and probably

some others

DMR

• Encoding: AMBE vocoder (AKA codec) (closed source) for Voice to Digital conversion

– 4FSK modulated carrier

• Frame Format: Based on ETSI (European Standards)

– “Open Standard”

– Next slide

DMR (is OPEN SOURCE)

ETSI standards:

• TS 102 361-1: Air interface protocol

• TS 102 361-2: Voice and General services and facilities

• TS 102 361-3: Data protocol

• TS 102 361-4: Trunking protocol

DMR Frame Format (Air Interface Protocol)

• 1st the basic structure


• The full structure


• Can transfer data or 2 voice channels

DMR Standards

• Tier 1

– FDMA

• Tier 2

– 2 Slot TDMA

– IP Site Connectivity (Vendor Specific)

• Tier 3

– 2 Slot TDMA

– Trunking

DMR Vendors

• DMR+

– Almost dead…

• DMR-MARC

– Still a lot, but looks like it’s dying…

• Brandmeister

– Looks like everyone is migrating to “BM”

DMR Vendors

• DMR+ – Originally Hytera Network

– Almost dead/gone

• DMR-MARC – CBridge, SmartPTT – Morotrbo (Motorola Solutions)

– Everyone has to connect via IP to a master controller, then a central server

– Still a lot in use, but looks like it’s dying…

• Brandmeister – Next slide

DMR Vendors

• Brandmeister (BM)

– Hytera, Mototrbo, Homebrew, MMDVM, DV4Mini, DVMega

– Everyone connects via IP to a central server

– Newest, worldwide growth

– Has more ways to interface

• Next slide

Brandmeister (BM) Interfaces

• For example, if you’re on DMR-MARC network, you can connect to TexasNet (BM TalkGroup 3148) through DMR-MARC TalkGroup 9000, which is linked to BM TalkGroup 3148

• Central Alabama has TalkGroup 31015, which is linked to WIRES-X (FUSION)

• Arkansas has TalkGroup 7227, which is linked to both WIRES-X and D-STAR

• Central Kansas has TalkGroup 31204, which is linked to WIRES-X, FUSION, and Analog

• These links are established through “DMR reflectors”, which are virtual “talkgroups” which can be linked to other talkgroups and other modes, such as D-Star and Fusion

DMR Map cqdmrmap.com

FDMA vs TDMA

D-Star vs DMR vs Fusion

• Flexibility

– D-Star and Fusion (with WIRES-X) can connect to any other (D-Star or Fusion) repeater in the world that’s registered

– DMR – the repeater operator decides which talk group(s) you have access to

• See www.dmrtexas.net

Common (BM) DMR TalkGroups Currently Used in Texas

• Updated: 9/17 • Talk Group ID Talkgroup Name Notes • 1 Worldwide Any Language • 2 Local/Metro Common Local Area Metro or Local Repeaters • 8207 Houston Area Local Activates all Upper Gulf Coast Repeaters • 3 North America United States/Canada (DMR-MARC) • 13 Worldwide English English Only • 310 TAC 310 North America Repeater-to-Repeater TG • 311 TAC 311 International Repeater-to-Repeater TG • 312 TAC 312 Repeater-to-Repeater TG • 1776 USA "USA 1776" by MITCOM • 3140 OK Statewide Now on the Brandmeister Network • 3148 Texas Statewide "Lonestar Talk Group" • 3100 DCI Bridge • 3106 NorCal Bridge • 3173 Mid-Atlantic WV/VA/MD/DE • 3174 Southeast AR/LA/MS/KY/TN/AL/FL/GA/SC/NC/PR • 3175 Southern Plains TX/OK/KS/AR • 3185 Cactus TX/AZ/CA • 99 Simplex TG for Simplex Use. Time Slot 1, Color Code 1 generally • 9999 NorCal Audio Test • Notes: Not a complete list of all Talk Groups.

Couple notes about DMR

• Talk Groups- a way for users to share a time slot • Zones - a group of individual channels • Color Codes - much like CTCSS(PL) or DCS on analog • Code Plugs - a radio’s configuration file • To access a DMR repeater, program the following in your radio:

– Frequency – Color Code – Talk group

• Talk-Around – Talking simplex on the repeater’s output frequency – Published simplex frequencies: 441.0, 446.5, 446.075, 433.45, 145.79,

145.51 to get off the repeater frequency – TG99, CC1, TS1 Generally accepted


• Survivability

– First, they’ll all work as repeaters “by themselves”

– Internet connectivity:

• D-STAR uses DNS, if one node goes down, no problem, you can connect to any other still on the internet – There is no reliance on a central control system

• DMR – if it loses connectivity to a central controller, it doesn’t work over the internet any more

• Fusion (with WIRES-X) – The central controller is in Tokyo, Japan…


• Survivability - what if the internet goes down? – Several references to people using Amateur Radio

Emergency Data Network (AREDN) to connect up D-STAR nodes, Fusion repeaters and DMR repeaters • Each has its own set of challenges in connecting to an

internet system not connected to the real internet (mostly to do with unknown background port activity)

– What is AREDN? • It's your typical store-bought home internet wireless router,

flashed with new software, set up as point-to-point links and meshed for throughput and reliability on a 10.0.0.0/8 subnet

– https://www.aredn.org

Current known locations of AREDN nodes


• For all three, there’s a device called a DV4Mini that allows you to access the internet; however:

– DMR

• Connects via reflector connections only (limited talk groups)

• Partial list of DMR reflectors next slide

– Fusion

• Can talk digital, but no WIRE-X

– D-Star

• This is only one of many ways to connect to the internet and there are new ones coming out regularly

Partial DMR Reflector List

http://www.va3xpr.net/brandmeister-talkgroups-reflectors/

Lot’s more…


• Manufactures

– DMR

• Has the most manufacturers

– D-STAR

• Icom is the main manufacturer but others manufacture cards to make their radios D-STAR compliant

– Fusion

• Yaesu only


• Connections

• Big difference between D-Star/Fusion and DMR

– D-Star/Fusion – you tell the repeater (or another device) what you want to connect to

– DMR – the repeater tells you what you can connect to


• Digital ID

– D-Star/Fusion send your call sign digitally every time you key up (meets Part 97 requirement)

– DMR… doesn’t (it sends a subscriber ID number)

• Voice Quality

– DMR/Fusion – good voice quality (12.5 Kbps)

– D-Star – sounds “mechanical” (6.25 Kbps)


• Concurrent Voice Channels

– DMR is the only mode which supports 2 different voice channels (time slots 1 and 2)

• Mixed mode

– D-Star does not support analog

– DMR can support analog

– Fusion was designed to support both digital and analog


• Published standards

– DMR

• …“Open standards” have a tendency to win in the long run

A few words on commercial “trunked” systems

• Encoding/Frame format: can be any number of what’s already been mentioned, and can be any number of frame formats

• Standards: – OpenSky System – APCO Project 16 – dPMR mode 3 – DMR Tier III – NXDN

• Kenwood has NEXEDGE Digital trunked radio • Icom IDAS Digital trunked Land Mobile Radio • Hytera DMR Tier 3 Trunking Lite • Motorola iDEN, Capacity Plus, Connect Plus, Harmony

Idea of trunked radio system

• Fix the problem in high density areas where there are more radio services required than spectrum has to offer

• Based on the idea that not EVERYONE is going to be talking on the radio AT THE SAME TIME

• Simple example following slides

Podunk Town, USA

• Police • Fire • EMS • City workers • Water • Electricity • Sanitation • School district • Animal control

• Frequency allocation for Podunk:

– 801 Mhz

– 802 Mhz

– 803 Mhz

• Only 3 radio channels for 9 services!!!

Basic idea of trunked radio system

• Every radio has a physical address • Each physical address is assigned to a group at the repeater • When one person in a group keys his radio, everybody else

in that group receives – If you’re not a member of that group, you don’t hear anything

• Every radio goes through a repeater which assigns the

physical frequency/channel dynamically • Of course, going through a codec which requires minimum

bandwidth also… • And these frames can have some sort of basic encryption to

prevent prying eyes from seeing what’s going on…

Podunk Town, USA

• Police radio keyed up, repeater assigns 801 Mhz

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Police radio keyed up, repeater assigns 801 Mhz

– 801 Mhz now in use

• Fire keys a radio, repeater assigns 802 Mhz

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Police radio keys radio, repeater assigns 801 Mhz



– 802 Mhz now is use

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Police radio keys radio, repeater assigns 801 Mhz




• Police finishes transmission, unkeys radio

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Police radio keys radio, repeater assigns 801 Mhz – 801 Mhz now in use

• Fire keys a radio, repeater assigns 802 Mhz – 802 Mhz now is use

• Police finishes transmission, unkeys radio – 801 Mhz now clear

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Fire finishes transmission, unkeys radio

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Fire finishes transmission, unkeys radio

– All channels clear

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Response to 1st fire is answered, repeater assigns 801 Mhz


• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA



• Response to 1st Police is answered, repeater assigns 802 Mhz

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA



• Response to 1st Police is answered, repeater assigns 802 Mhz


• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• Response to 1st fire is answered, repeater assigns 801 Mhz – 801 Mhz now in use

• Response to 1st Police is answered, repeater assigns 802 Mhz – 802 Mhz now is use

• EMS keys radio to transmit, repeater assigns 803 Mhz

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA


• Response to 1st Police is answered, repeater assigns 802 Mhz – 802 Mhz now in use

• EMS keys radio to transmit, repeater assigns 803 Mhz – 803 Mhz now in use

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA


• Response to 1st Police is answered, repeater assigns 802 Mhz – 802 Mhz now in use

• EMS keys radio to transmit, repeater assigns 803 Mhz – 803 Mhz now in use

• Trunking system now MAXED OUT!

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• City worker tries to key a radio, doesn’t get the “beep” to start talking

• Police unkeys

– Frees 802 Mhz

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• City worker tries again, repeater now gives 802 Mhz to him

– At the same time, Fire finishes and EMS finishes

• 801 Mhz

• 802 Mhz

• 803 Mhz

Podunk Town, USA

• City worker tries again, repeater now gives 802 Mhz to him

– At the same time, Fire finishes and EMS finishes

• Two others now available for whoever keys up next

• 801 Mhz

• 802 Mhz

• 803 Mhz

Trunked Radio Systems

• So, you just need a good idea on peak times to know how many actual channels you need based on how many services are going to be connected and the busiest times

• Many old fashioned telephone trunking algorithms to figure this out fairly accurately

• It comes down to probabilities

Trunked Radio Systems

• So who’ll be the first to come up with a “trunked ham repeater system”?

ham digital modes - longview/east texas amateur …€¢“digital smart technologies for amateur...

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