User's Manual

10.2.1 RX FREQUENCY TRIM
The RX Frequency Trim trims the unit on frequency during receive. This setting, if incorrect, may
degrade receive sensitivity, distortion, and possible recovered audio level, which in turn affects
AUX OUT (RX) Gain and Audio PA Gain. The receive frequency trim is not affected by any other
alignment step.
To determine if the receiver is correctly trimmed to frequency, the 1
st
local oscillator frequency
must be measured. DO NOT KEY THE UNIT DURING THIS PROCEDURE AS SERIOUS
DAMAGE TO THE COUNTER MAY RESULT!
A channel with a receive frequency programmed into it should be selected. The correct local
oscillator will be displayed on the programmer channel box. The frequency on the counter should
be observed and the RX Frequency Trim value adjusted for least error. Because of the very low
local oscillator level at the antenna terminals, the frequency counter may not be able to read the
frequency. If so, perform the TX Frequency Trim adjustment detailed later and set the RX
Frequency Trim value to match that of the proper TX Frequency Trim value.
10.2.2 AUX OUT GAIN
To set the AUX OUT gain, an RF signal generator must be connected to the DTX module. Its
frequency should be set to that of a programmed channel. The generator should be modulated at
the desired deviation, typically 60 % of maximum, with a 1 kHz tone. The RF output level is not
critical, but should be above any squelch threshold which may have been set. –70 dBm should
be sufficient. If not, squelch can be disabled via the settings menu of the programmer for this
procedure.
With an oscilloscope connected to the AUX OUT output, the AUX OUT Gain setting should be set
to value which produces the desired output level. Note that the output impedance of the AUX
OUT is about 600 ohms. If the load impedance of the load that will be connected to this output is
less than 10 k or so, a resistor of a value equal to the load impedance should be connected to
the AUX OUT output when making the adjustment.
10.2.3 AUDIO PA GAIN
To set the Audio PA gain, an RF signal generator must be connected to the DTX module. Its
frequency should be set to that of a programmed channel. The generator should be modulated at
the desired deviation, typically 60 % of maximum, with a 1 kHz tone. The RF output level is not
critical, but should be above any squelch threshold which may have been set. A –70 dBm level
should be sufficient. If not, squelch operation can be disabled via the settings menu of the
programmer.
With an oscilloscope connected to the AUDIO OUT output, the AUDIO OUT Gain setting should
be set to value which produces the desired output level.
10.2.4 CARRIER DETECT ON AND CARRIER DETECT OFF
The Carrier Detect On and Carrier Detect Off settings control the RF level (or Signal-to-noise
ratio) at which the DCD output goes true and what level at which it goes false. To prevent
chattering on noise, these two settings are not normally the same. 3 to 5 dB of hysteresis is
usually provided i.e. if the RF signal level is increased from zero, at some point, the DCD output
will go from false to true. The RF level may then have to be decreased by several dB before the
DCD output goes false again. This prevents chattering with signal levels near the carrier detect
level. If squelch is enabled, the received audio muting will follow the DCD output. The desired
carrier detect levels can be directly entered via the alignment screen in dBm and then fine tuned
with a high quality signal generator, if necessary.
To determine the state of the DCD output, connect a DC coupled oscilloscope or DVM to the
DCD output. It may help to disable the squelch via the Monitor input or Monitor button on the
programmer so that the received audio signal can be continuously observed i.e. not squelched
when DCD is false.