You too can join in this proposal... feel free to e-mail me with comments.

HamTone Technical Summary:
(Tailored for 70cm -- "Tyro class" -- Amateur Radio repeater systems)

What is it?

  • HamTone is a subaudible data protocol first designed for Amateur FM repeaters.
  • It replaces CTCSS (e.g., PL, CG, DCS) with subaudable data that frequency modulates the radio carrier with baseband energy contained between 60Hz and 155Hz using a modulation index just short of three (quite like CTCSS). It uses sinusoidally shaped Manchester coded minimum frequency shift data transmissions. Similar techniques have been used in trunked radio systems for decades. There is more detail below.
  • HamTone can key repeaters, shut them down, mute repeated audio, link repeaters together, manage a phone-patch, identify the repeater, give the repeater's location, explain repeater access requirements, transmit the time, date, and more.
  • It can also identify the repeated mobile, display that mobile's latitude and longitude, identify which system the mobile is using to access a linked network, report the mobile's frequency error and peak deviation.
  • It does this without obscuring the voice conversation.
  • It is also extensible... transparently allowing various low data rate transfers to accompany the voice transmission.
  • A continuous string of HamTone zeros is identical to CTCSS tone and three standard CTCSS frequencies are used to transmit HamTone data:
    ... an "A" System uses 123 Hz
    ... a "B" System 136.5 Hz and
    ... a "C" System 151.4 Hz.
  • Repeaters using HamTone can still be used by radios only able to send A, B and C System tones; the repeater controller simply sees this as a mobile not sending data.
  • Like CTCSS, having three tones is useful toward reducing co-channel interference. Unlike the current use of CTCSS, Amateurs traveling to new locations can readily find the correct tone when the choices are limited to just three...
    ...because of the "party-line" nature of Amateur Radio, more tones are not needed.
  • Also like CTCSS, HamTone design expects to control radio and Internet connections with signal strengths at least adequate for 12dB SINAD voice quality. Thus, the HamTone protocol does not include feed-forward error correction and only includes minimal error detection. The protocol is simply designed to control voice quality Amateur repeater systems and will disconnect signals too poor for analog voice.

    Why yet another scheme?

    The short answer: it has a set of features not found in another single scheme. But, there is MUCH more. HamTone is part of a larger plan addressing issues that confront Amateur Radio.

    I will soon petition the Federal Communications Commission (FCC) to change the Amateur Radio Rules (Part 97) asking for a new class of Amateur license and setting aside a sub-band of our 70 cm frequencies dedicated to narrow-band FM voice using both simplex and repeaters. While shared by all Amateurs, this sub-band would be the only spectrum available to the proposed new entry-level license.

    This new Tyro license would be particularly useful for recruiting youth and involving the whole family in the Amateur Radio enterprise. The proposal intends to increase both the interest in Amateur Radio and its numbers.

    The Petition will ask the Commission to establish 99, 12.5 Khz spaced narrowband (11F9W) channels... each having a data sub-channel below 200 Hz. and a voice or data sub-channel from 300 to 3000 Hz.

  • 79 paired duplex repeater channels and 20 simplex only channels
  • ....repeater input channels centered from: 430.0125 to 430.9875 MHz
  • ..repeater output channels centered from: 439.0125 to 439.9875 MHz
  • ...simplex channels centered from: 438.7625 to 439.0000 MHz
  • channels numbered from 1 through 99 (decending in frequency):
  • 1 -- the first repeater pair -- centered at: 430.9875in/439.9875out
  • 79 -- the last repeater pair -- centered at: 430.0125in/439.0125out

    A beacon channel pair (Channel Zero) is operated as an automated remote base station. Its transmissions are centered at 439.9975 MHz. It receives control and informational data on 430.0025 MHz from a control station.

  • Channel Zero is an especially narrow, with an occupied bandwidth of 5 KHz (5F7W).
  • beacons will transmit identification and information using HamTone protocol and ASCII characters.
  • These beacons can be used for propagation tests, information about local systems as well as other information useful to the Amateur service. They do not transmit voice. If used, Morse code identifiers must limit their tone frequencies and peak deviation (e.g., a 500 Hz tone @ 1 KHz deviation).
  • Transmitting on Channel Zero (input or output) is restricted to Technician, General, Advanced and Extra class Licensees.
  • Beacon control is not limited to 430.0025 MHz nor is the use of 430.0025 limited to controlling Channel Zero beacons. Notwithstanding its actual use, 430.0025 MHz is limited to 5F7W transmissions.

    Having the Commission prescribe standardized protocols on a narrow sub-band of "repeater frequencies" will help Amateur Radio grow, flourish, further pursue and even expand its purpose. Using this instant poposal, the Commission can spawn the kind of ubiquity and cultural growth achived by several prior winning standards.

    DRAFT...NOT YET DONE... changes coming...

    This Petition has its foundation in Amateur radio's purpose... especially that found at: Part 97.1 (c) "Expansion of existing resevoir within amateur radio service of trained operators, technicians, and electronics experts." It pursues that goal and more.

    Moreover, this proposal encorages Amateur Radio to become even more involved in scientific research and public service. Further, the proposal will ask the Commission to make it clear that the spectrum from 430-to-440 MHz is assigned to the Amateur Radio Service on a primary basis.

    A Tyro license would require a short test limited to operational requirements and etiquette. It would be adminstered "on-line" and proctored (verified) by any Amateur Licensee with a Technician or higher class license. Successful applicants would have a license and callsign (perhaps an FRN) issued "instantly"... using the Commission's Internet Universal Licensing System (ULS). The license fee and expiration would be the same as other Amateur licenses. The callsign issued by the computer would be entered into the licensee's transceivers and HamTone would include that callsign in each transmission. Applicants must be thirteen years of age or older.

    The Tyro license is restricted to the use of radio transmitters crafted for this class of service. Such transmitters would use HamTone to broadcast the serial number of the transmitting unit (as assigned by its manufacturer or the Amateur licensee -- Technician or higher -- that modified an existing radio for this service) as well as the call sign of the licensee using it. Tyro class usage of these transceivers would be limited to 50 Watts of output power and restricted to a sub-band of ninety-nine 12.5 kHz wide channels located within the 70 cm Amateur Radio band. Tyro licensees can operate mobiles, portables and small base stations (50 Watts or less); they cannot be the licensee for a repeater.

    Channel Organization

    The first seventy-nine of these channels would be repeater pairs. Twenty more would be simplex only channels. The channels are referenced by channel number starting with 1, going through 99. Channel 1 would be the sub-band's highest frequency... centered at 439.9875 for the repeater output; that output frequency is paired with 430.9875 as the repeater input side of the channel. The channel 2 pair would be: repeater output = 439.9750 with a 430.9750 MHz input. Each sequentialy assending channel pair would be spaced 12.5 kHz lower in frequency through the last repeater pair, channel 79; its output is 439.0125 with a 430.0125 input.

    The repeater input/output split for this sub-band is 9 MHz. Mobiles transmit on the lower frequency, repeaters transmit on the higher frequency. This split facilitates small low cost duplexers for both repeaters and mobiles.

    Channel 80 -- centered at 439.0000 MHz. -- begins the simplex only portion of the sub-band. Channel 81 is at 438.9875 MHz and each assending channel number is centered 12.5 kHz lower in frequency than the preceeding channel. The last channel -- channel 99 -- is centered at: 438.7625 MHz

    While simplex (or talking around the repeater) is permitted on all the repeater output frequencies, it is not permitted on the 79 inputs located from 430.9875 down to 430.0125. Further, talk-around simplex users must be aware that repeater users may not be able to hear them and must tolorate subsequent interference. Notwithstanding, talk-around is a handy way to use simplex between closely located mobiles while still hearing calls on the repeater.

    This sub-band plan requires a maximum mobile receiver band-spread of only 1.25 MHz. This allows fairly high "Q" receiver front-end while not demanding electronic tuning. The transmit band-spread is 10 MHz... quite achiveable with current design techniques.

    Frequency Coordination Requirements

    Channels 1 through 50 require frequency coordination from the appropriate local coordinating groups. These repeaters are intended for wide area coverage systems with relitively permanent locations. Such systems may be used by any Amateur Radio Licensee so long as such users obey the repeater usage rules established by the repeater licensee and approved by the local coordinating groups. The local coordinating groups will provide a website containing their contact information. This website will further contain information on each coordinated repeater, including: its latitude, longitude, access Barker Code, effective radiated power (ERP), antenna heighth above average terrain (HAAT), operationl status and the repeater licensee's contact information.

    Channels 51 through 99 are not formally coordinated and must be shared using the normal Amateur Radio conventions. Repeaters and base stations using these channels may be quite temporary and mobile. Again, simplex activity using channels 51 through 79 must expect unintended interference from repeaters sharing the channel. While use of these channels are not geographically limited by local coordinating committees, such committees may require sharing measures when interference and/or traffic intensity dictates. For example, duplex frequency use may require monitoring the output frequencies to prevent interference.

    On this sub-band, the local repeater licenssess and their coordinating committees are responsible to resolve frequency and system conflicts. All affected licensees are expected to cooporate in this effort. Failing that, the Commission will resolve remaining spectrum related conflict.

    Channel Organization

    On channels 1 through 79 users would select a channel and switch between the repeater or talking-around the repeater. If they intended to talk through a repeater, they would also need to select -- from a choice of four -- the correct code for the intended repeater using that channel.

    The repeaters on these channels would be voluntarily provided by the higher class Amateur Radio licensees in each local area. The detailed and specific usage rules for these repeaters and the spectrum they occupy would be developed and enforced by the local repeater licensee and their local repeater councils using the broad guidelines provided by Part 97. The Commission would only manage local issues when the local resolution failed.

    This is primarily a mobile (including hand-helds) radio service... with fixed radios limited to coordinated repeaters and small base stations with restricted coverage. These activities would be locally managed within the guidelines set forth in a new portion of Part 97. The spectrum from 430 to 431 MHz and 439-440 MHz would be channelized for the 79 channel pairs. Repeater inputs and outputs would be separated by 9 MHz. The repeaters would transmit on the higher frequency -- inputs low.

    While the frequencies from 439-440 would primarily used for the repeater outputs, they can be used for "talk-around" simplex activity by hand-helds, mobiles, and small base stations.

    Simplex activity is not permitted on the repeater input frequencies (430-431 MHz).

    Channels one through sixty-nine would be reserved for wide-area coordinated repeaters with fixed locations. Channels seventy through seventy-nine are reserved for uncoordinated repeaters with temporary locations.

    This spectrum has the advantage of being available to Amateur Radio world-wide. This maximizes the economies of scale potentially making radios manufactured for this service useful in all three Regions.

    In the United States, it does not unduly perturb current band-plans. Moreover, this plan allows repeater diaspora from the current dissonance... perhaps, voluntarily freeing spectrum for more advanced Amateur uses.

    Further, this plan helps Amateur Radio recruit, motivate and train young initiates (tyros) to its pursuit while allowing more populace support for exigent activities. Moreover, HamTone improves user accountability by thwarting anonymous transmission. Finally, it creates jobs.

    More HamTone Detail:

  • HamTone supports data rates just over 18 ASCII characters per second.
  • Data are sent in variable length frames always starting with a prefix then an 11 symbol Barker sequence. The Barker sequence is used to sync receiving clocks and key repeaters.
  • Actually, the full Sync pattern is the 11 symbol Barker code preceeded by three added symbols. These mitigate a direct current bias in the Barker sequence. So, Sync is 14 symbols long. HamTone Sync patterns restrict energy below 50 Hz. Moreover, for each transmission, Sync helps the decoder find the center frequency. Decoders likely ignore these prefix symbols as only a hardware set-up metric.
  • In 47 ms the repeater identifies a valid signal meant for it and keys its transmitter. Then, it usually repeats the data received on this control channel (40-200 Hz) and the traffic heard on its voice channel (300-3000 Hz).
  • Decoders see two symbol states: mark and space... each symbol takes 3333uS.
  • Symbols are generated by symmetrically shifting the carrier frequency above and below the center frequency.
  • The frequency shift slew rate is shaped to that of a half-wave 150Hz sine wave.
  • HamTone can also be described as: Sinusoidal Minimum Shift Keying (SMSK)
    see also, David J. Cohen, NTIA Report 84-168
  • Mark and space can be either a frequency shift higher than channel center (+) or a shift lower than center (-).
  • Using positive transmission modes, +mark state is when the carrier frequency deviates above center frequency and -space with carrier below center.
  • Negated transmission modes are also used: -mark below center, +space above.
  • This allows two separate schemes by simply inverting the discriminator and modulator. The rest of the encoder/decoder looks the same.
  • Further, the Barker sequence order is sent both forward and backward... needing only a flow direction change in encoders and decoders.
  • This gives 4 transmission modes (tm) governed by the Sync sequence detail (+ symbol is above center frequency, - is below):
  • * tmA (forward, positive) ++- +++---+--+-,
  • * tmB (forward, negated) --+ ---+++-++-+,
  • * tmC (reversed, positive) +-+ -+--+---+++,
  • * tmD (reversed, negated) -+- +-++-+++---.
  • [Above, the prefix is shown separated from the Barker sequence.]
  • These four modes mitigate co-channel interference when coverage overlaps.
  • Transmitters select one of these four modes; receivers could adjust to any.
  • When the expected sync is received, receivers become in-sync and begin to transfer data to the controller.
  • When in-sync the timing of the clock is known and what follows is a data frame.
  • Primary data organization is Manchester encoded eight-bit bytes assembled into frames.
  • Manchester encoded bits consist of two opposite state symbols with a clock edge between them; a bit always has a clock edge at its center.
  • The HamTone data scheme limits the data bandwidth to about 1.5 octaves. There is no D.C. component so, the center frequency does not get lost after detection. If the center frequency drifts, the decoder can track it. Again notice, the Barker sequence is actually transmitted with a three symbol prefix helping the decoder to find the carrier's center frequency and remove energy content below 50 Hz.
  • The Barker sequence puts the decoder in-sync such that the timing of the receive clock is known.
  • Because of the Manchester encoding and the nature of the Barker sequence, the Barker sync sequence is not found in data... regardless of phase slippage. Notice above, the Barker sequence has three adjacent like symbols... Manchester encoded data never has more than two adjacent same-state symbols. Again, valid data bits always have opposite symbols ether side of the clock (CLK) edge.
  • Since negation/inversion is adjusted prior to the decoder, bit decoding is always the same: true bit=mark/CLK/space, false bit=space/CLK/mark.
  • Frames start with Sync followed by a required four-byte field containing a 32 bit unsigned integer sent most significant bit first which is the serial number of the unit originating the frame (4 billion combinations).
  • The second required field contains the Amateur call sign as ASCII char. The call sign is terminated with an ASCII null (0). If the radio does not have an Amateur call programmed, the second field contains only the null.
  • The third and final required field starts with a byte (unsigned integer) describing what follows; the first 16 values are reserved for system control. Values greater than 15 are available to future developers. A value of zero in this field defines it as empty. The meaning of the first 16 values will be defined here later.
  • As long as a valid signal is sent to the repeater input, the originating radio repetitively sends frames containing redundant required fields. Optional fields may change... but, not the required fields.

    Who can use this

    I intentionally place this scheme into the public domain so that all of Amateur Radio can freely use it. In short, it is an open architecture... no royalties, no contracts, no copyrights; just use it. I will publish test reports and the evolving specifications here.

    GMRS/FRS Plan - NPRM 10-119  

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    Last modified: Jun 26, 2017