<?xml version="1.0" encoding="UTF-8"?>

<section xml:id="introSimplex" 
         xmlns="http://docbook.org/ns/docbook" 
         xmlns:xlink="http://www.w3.org/1999/xlink" 
         xmlns:xi="http://www.w3.org/2001/XInclude">

<info>
  <title>DMR Simplex Operation</title>
</info>

<para>
  The most simple form of a DMR QSO<footnote><para>QSO is a code for call or connection between two 
    amateur radio stations.</para></footnote> is the simplex QSO. That is a direct connection between 
    two two DMR radios. Like for the DMR repeater operations, this could be a private, group or 
    so-called <glossterm>All Call</glossterm>. 
</para>

<example xml:id="figIntroSplxPc">
  <title>Simplex private call.</title>
  <mediaobject>
    <imageobject><imagedata fileref="fig/simplex_privatecall.png" width="7cm" align="center"/></imageobject>
  </mediaobject>
</example>

<para>
  In <xref linkend="figIntroSplxPc"/> a simple simplex private call from DM3MAT to DL1XYZ is shown 
  as well its reply. Both operators transmit and receive on the same frequency (here the DMR calling
  channel at 433.450 MHz). Although other operators are in the area (DL2XYZ &amp; DL3XYZ) which 
  receive the signal, their radios remain silent. This is because this is a private call to a 
  specific operator and only the radio of that operator will receive the call. All other radios will ignore the
  call. The channel, however, remains occupied during that call. 
</para>

<para>
  At that point it is worth mentioning, that if DL1XYZ answers directly to the initial call by 
  pressing the PTT, he will answer with a private call to DM3MAT. He does not need to search for
  number of DM3MAT in his address book. The direct answering to calls is only possible for several
  seconds after the end of the initial call. After that period (called <glossterm>Hang 
  Time</glossterm>) a press on the PTT will start a call to the default contact (see 
  <xref linkend="introCPChannel"/>) associated with the simplex channel.
</para>

<example xml:id="figIntroSplxGc">
  <title>Simplex group call</title>
  <mediaobject>
    <imageobject><imagedata fileref="fig/simplex_groupcall.png" width="7cm" align="center"/></imageobject>
  </mediaobject>
</example>

<para>
  It is not only possible to call single operators in simplex mode. Also groups can be called using
  group calls. A common talk group for the simplex mode has the number 99, (TG99, for <quote>talk 
  group 99</quote>). These group calls are then received by all radios that are configured 
  accordingly. Like for the repeater operation, also in simplex mode, the radio needs to know which 
  groups the operator belongs to and therefore, which talk groups to receive on which channels. This 
  is done using so-called <glossterm>Group List</glossterm>s, which are discussed later.
</para>

<para>
  In <xref linkend="figIntroSplxGc"/> such a simplex group call is shown. There DM3MAT calls the 
  talk group TG99. As DL1XYZ as well as DL2XYZ configured their radios to receive that call on 
  simplex channels, they do so. DL3XZY did not, so he does not receive the call. DL1XYZ &amp; 
  DL2XYZ can now respond to that call by pressing on the PTT within the hang time irrespective of 
  their default contact for the channel. 
</para>

<example xml:id="figIntroSplxAc">
  <title>Simplex all call</title>
  <mediaobject>
    <imageobject><imagedata fileref="fig/simplex_allcall.png" width="7cm" align="center"/></imageobject>
  </mediaobject>
</example>

<para>
  To be sure that a simplex call gets received by all operators in the area, a so-called 
  <glossterm>All Call</glossterm> should be used. This is a special call type to the reserved 
  number 16777215, that gets received by all radios irrespective of their configuration. For the 
  <xref linkend="figIntroSplxAc"/>, the all call by DM3MAT gets received by all operators including 
  DL3XYZ. By directly answering within the hang time, all participants are able to respond to that 
  call with an all call as well. 
</para>

<note>
  <para>
    In short: A DMR channel consists of a transmit and receive frequency (identical on simplex channels), 
    a default contact that gets called whenever the PTT button is pressed and a list of group calls 
    the radio will receive on that channel. 
  </para>
</note>

<table xml:id="tabIntroSimplexFreq">
  <title>DMR simplex frequencies</title>
  <caption>The list of eight common DMR simplex channels. The channel S0 is the calling channel.</caption>
  <thead>
    <tr><td>Name</td><td>Frequency</td><td>Name</td><td>Frequency</td></tr>
  </thead>
  <tbody>
    <tr> <td>S0 (call)</td><td>433.4500 MHz</td> <td>S4</td><td>433.6500 MHz</td></tr>
    <tr> <td>S1</td><td>433.6125 MHz</td> <td>S5</td><td>433.6625 MHz</td></tr>
    <tr> <td>S2</td><td>433.6250 MHz</td> <td>S6</td><td>433.6750 MHz</td></tr>
    <tr> <td>S3</td><td>433.6375 MHz</td> <td>S7</td><td>433.6875 MHz</td></tr>
  </tbody>
</table>

<para>
  <xref linkend="tabIntroSimplexFreq"/> lists the common simplex channel frequencies. The channel 
  S0 is the calling channel. Especially in densely populated areas, you should switch to another 
  channel for the actual QSO and use S0 only for the initial call.
</para>
</section>
