Operating instructions

1892 1344 - SX450G Transceiver Operator Guide v1.7 / Nov 2007 9
OVERVIEW OF FREQUENCIES AND PROGRAMMING
Each radio is built to order to cover a band (the switching bandwidth) of 20MHz within the
range 400 - 470 MHz. Each radio is also manufactured to work with a particular channel
width of 12.5kHz, 20kHz or 25kHz. These are fixed parameters, and cannot be changed
by the user.
Within the switching bandwidth, the unit can transmit and receive on any frequency
(provided it is a whole multiple of the comparison frequency), and up to 256 frequencies
can be stored as numbered channels 0 to 255.
There can also be an offset between transmit and receive frequencies. You can program
this offset, but both transmit and receive frequencies must remain within the switching
bandwidth for all channels. For example:
Switching bandwidth = 450MHz to 470MHz (fixed at manufacture)
Rx offset = +5MHz (programmed by user)
Therefore, maximum Tx frequency allowable = 470MHz - 5MHz = 465MHz.
During use, an operational channel can be selected at any time either using logic lines or
a serial data input. Logic lines can only select channels 0-63, serial commands can
select any channel.
Before the unit leaves the factory, each of 256 channels is allocated to a frequency, but
you can reprogram them if you wish.
You can program the unit in one of two modes:
v 256-channel mode: All 256 channels 0-255 can be programmed, but as a
block by entering a starting frequency and a step size, so that they contain
uniformly spaced frequencies. A single Rx offset applies to all channels.
v 80-channel mode: Each of channels 0-79 can be individually programmed
with any frequency, but the remaining channels 80-255 are not available for
use. Individual Rx offsets may be applied to channels.
One channel is then nominated as the operational channel.
To program a unit, you need to read the existing data from the it, edit the data using a
special program supplied by Wood & Douglas (SXn50.EXE), which runs on a PC under
Windows, then write the data back to the unit. This software provides facilities, such as a
list of valid frequencies, and the ability to copy one channel’s details to a number of
others, to make the job easier. Programming is described in Part Two of this manual,
starting on page 13.