User's Manual

10.2.5 TX LOW POWER AND HIGH POWER
The transmitter output power level can be programmed on a per channel basis via the alignment
page of the programmer. If RNet Compatibility has not been programmed on the settings page,
both the low and high power levels can be set. If RNet Compatibility has been programmed, only
high power can be set. The TX High Power and TX Low Power settings in the TX Power box act
to select a common value for all channels. Individual values for each channel can be entered in
the per channel boxes at the bottom of the screen. Power is set in watts with a resolution of 0.1
watt. The power level can be confirmed and fine tuned, if desired, by connecting the radio to an
accurate wattmeter.
10.2.6 AUX IN GAIN
To set the Aux In gain, an audio oscillator or appropriate signal source (e.g. modem) should be
connected to the Aux In input at the desired input level. An FM deviation meter should be
connected to the antenna connector through a suitable attenuator or coupler. The unit should be
keyed for transmit and the Aux In gain should be adjusted for the desired deviation, typically 60
% of rated deviation.
10.2.7 TX FREQUENCY TRIM
This setting is used to trim the transmitter to frequency. This value should not normally need
adjustment. However, as the unit ages and/or if the transmitter power or the Aux In gain is
changed significantly, slight corrections may be prudent. Note: Any adjustments must be made
at a unit temperature of 25 +/- 2 C (77 +/- 1.8 F). Due to internal heating, this adjustment must
not be made after the unit has been transmitting unless it has been allowed to cool to the correct
temperature. Likewise, the adjustment itself should be made as quickly as possible.
The unit should be set to a channel which is at an output power which is close to what will be
used the majority of the time. The RF output of the unit should be coupled to a frequency counter
through a suitable attenuator or coupler. Ensure that no modulation source is connected to the
MIC IN or AUX IN. The PTT should be activated and the TX Frequency Trim value adjusted for
the correct frequency. The value can be changed while the unit is transmitting.
10.2.8 DEVIATION AND BALANCE
The deviation adjustments are used to set the maximum limiting deviation of the transmitter. This
must be set properly to ensure that the unit will meet the regulatory spurious emissions
requirements, in particular, occupied bandwidth. The balance adjustment is used to ensure a
proper relationship between the modulating signal to the reference and to the VCO. If the ratio
i.e. balance is not correct, the transmit audio frequency response will not be correct which could
result in a distorted data waveform.
The optimum values for deviation and balance vary in a predictable manner as a function of
carrier frequency. In order to relieve the user of having to adjust deviation and balance each time
a transmit frequency is entered or changed, the radio calculates the required values based upon
the correct values for two special alignment frequencies. These required values have already
been determined at the factory and are stored in the unit. As transmit frequencies are entered or
changed, new calculated values will appear in the per channel boxes at the bottom of the screen.
These values can be changed on a channel by channel basis, if desired.
The procedure detailed here is for setting the deviation and balance at the special alignment
frequencies so that the deviation and balance will be correct at any programmed frequency. This
same procedure can be used to set any given channel values in the per channel boxes.
An FM demodulator should be connected to the RF output of the module through a suitable
power attenuator or coupler. The demodulator filters should be set for no de-emphasis, as low a
highpass cutoff as possible (<50 Hz, preferably down to DC), and a lowpass cutoff of
approximately 15 kHz. The demodulator output should be connected to an oscilloscope so that it
can be observed.
An audio oscillator should be connected to the AUX IN input. The output waveform should be
sine, the level at zero, and at a frequency of 500 Hz. Confirm that the Aux In Gain value is at least
10.