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<html><head><title>THOR Modes</title></head><body bgcolor="#ffffcc" link="#cc0088" text="#666644" vlink="#995544">
<font face="Verdana, Arial, Helvetica" size="-1">
</font><h1><font face="Verdana, Arial, Helvetica" size="-1">THOR Modes</font></h1>
<p>
</p><hr>

<h3><font face="Verdana, Arial, Helvetica" size="-1">General Description</font></h3>
<font face="Verdana, Arial, Helvetica" size="-1">THOR is a family of
offset incremental multi-frequency shift keyed modes with low symbol
rate, closely related
to DominoEX. A single carrier of constant amplitude is stepped between
18 tone frequencies in a constant phase manner. As a result, no
unwanted sidebands are generated, and no special amplifier linearity
requirements are necessary. The tones change according to an offset
algorithm which ensures that no sequential tones are the same or
adjacent in frequency, considerably enhancing the inter-symbol
interference resistance to multi-path and Doppler effects.
</font><p>
<font face="Verdana, Arial, Helvetica" size="-1">The mode has full-time
Forward Error Correction, so is extremely robust. The default speed (11
baud) was
designed for NVIS conditions (80m at night), and other speeds suit weak
signal LF, and high speed HF use. The use of incremental keying gives
the mode complete immunity to transmitter-receiver frequency offset,
drift and excellent
rejection of propagation induced Doppler.
</font></p><p>
<font face="Verdana, Arial, Helvetica" size="-1">The mode was developed by Dave W1HKJ, and is an extension of DominoEX by Con ZL2AFP and Murray ZL1BPU.
</font></p><h3><font face="Verdana, Arial, Helvetica" size="-1">Protocol</font></h3>
<font face="Verdana, Arial, Helvetica" size="-1">These are unconnected,
manually controlled message asynchronous symbol synchronous simplex
chat modes, using binary convolutional
Forward Error Correction. The default calling mode is THOR11.
</font><h3><font face="Verdana, Arial, Helvetica" size="-1">Coding and Character Set</font></h3>
<font face="Verdana, Arial, Helvetica" size="-1">A binary varicode with ASCII-256 user interface (same as MFSK16) is used. Lower case characters are sent faster. An ASCII-128
secondary character set extension allows a fixed (typically ID) message to be sent whenever the transmitter is idle.
Modulation uses two dibit pairs, symbol synchronous, differential.
</font><p>
<font face="Verdana, Arial, Helvetica" size="-1">The FEC system uses binary convolution to generate two dibits per varicode bit, and halves the corrected data rate
compared to the equivalent DominoEX mode. Rate R=1/2, Constraint length K=7, Interleaver L=10 (40 bits). This is a NASA
standard system.
</font></p><h3><font face="Verdana, Arial, Helvetica" size="-1">Operating Parameters</font></h3>
<table bgcolor="#eeeeff" border="1">
<tbody><tr bgcolor="#eeffff">
<td><small><b>Mode</b></small></td>
<td><small><b>Symbol Rate</b></small></td>
<td><small><b>Typing Speed<sup>1</sup></b></small></td>
<td><small><b>Duty Cycle<sup>2</sup></b></small></td>
<td><small><b>Bandwidth<sup>3</sup></b></small></td>
<td><small><b>ITU Designation<sup>4</sup></b></small></td></tr>
<tr>
<td><small>THOR4<sup>5</sup></small></td>
<td><small>3.90625 baud</small></td>
<td><small>~ 1.25 cps (12 wpm)</small></td>
<td><small>100%</small></td>
<td><small>173 Hz</small></td>
<td><small>173HF1B</small></td>
</tr><tr>
<td><small>THOR5<sup>5</sup></small></td>
<td><small>5.3833 baud</small></td>
<td><small>~ 1.6 cps (16 wpm)</small></td>
<td><small>100%</small></td>
<td><small>244 Hz</small></td>
<td><small>244HF1B</small></td>
</tr><tr>
<td><small>THOR8<sup>5</sup></small></td>
<td><small>7.8125 baud</small></td>
<td><small>~ 2.5 cps (25 wpm)</small></td>
<td><small>100%</small></td>
<td><small>346 Hz</small></td>
<td><small>346HF1B</small></td>
</tr><tr>
<td><small>THOR11<sup>6</sup></small></td>
<td><small>10.766 baud</small></td>
<td><small>~ 3.5 cps (35 wpm)</small></td>
<td><small>100%</small></td>
<td><small>262 Hz</small></td>
<td><small>262HF1B</small></td>
</tr><tr>
<td><small>THOR16</small></td>
<td><small>15.625 baud</small></td>
<td><small>~ 5.0 cps (50 wpm)</small></td>
<td><small>100%</small></td>
<td><small>355 Hz</small></td>
<td><small>355HF1B</small></td>
</tr><tr>
<td><small>THOR22</small></td>
<td><small>21.533 baud</small></td>
<td><small>~ 7.0 cps (70 wpm)</small></td>
<td><small>100%</small></td>
<td><small>524 Hz</small></td>
<td><small>524HF1B</small></td>
</tr></tbody></table>
<font face="Verdana, Arial, Helvetica" size="-1"><small><br><b>Notes:</b><br>1.
WPM is based on an average 5 characters per word, plus word space.
Values are approximate because a variable length code is used.<br>
2. Transmitter average power output relative to a constant carrier of the same PEP value.<br>
3. This is the "Necessary Bandwidth" as defined by the ITU.<br>
4. A summary of the ITU Designation system can be found at <a href="http://en.wikipedia.org/wiki/Types_of_radio_emissions">http://en.wikipedia.org/wiki/Types_of_radio_emissions</a><br>
5. Double spaced mode.<br>
6. Default and normal calling mode.</small></font></body></html>

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