DANIELS
ELECTRONICS LTD.
TM
4-6
IM10-VR3H040-AB VHF Enhanced Extra Wideband Receiver Instruction Manual
4.7
Main Board Tuning
4.7.1
IF Amplifier Bias Current Adjustment
Monitor test point TP5 and adjust MOSFET bias potentiometer R13 until a DC level of +8.75
Vdc is achieved. This corresponds to an IF amplifier drain current of 7.5 mA, and prepares the
IF amplifier for following alignment steps. Note that an incorrectly set bias point can add
substantially to the overall receiver current consumption.
4.7.2
21.4MHz
•
Connect the Rx main board to the power supply and place the switch on the front panel
to the ‘NORM’ position.
•
Place the Marconi test set into 'Tx Monitor' mode and monitor the radiated RF from X1
using a test probe or antenna with the 1 watt input. Tune C130 to achieve 21.855MHz
±
20 Hz.
•
Place the test set into 'Rx Test' and inject the receiver nominal frequency into the RF
input of the front end. RF Level = –70 dBm, mod freq = 1kHz, deviation = 9kHz.
Ensure the band-pass filter of 0.3–3.4kHz is selected.
•
Measure TP5 and adjust R13 to achieve 8.75V
±
0.1V
•
Adjust coil L5 for highest audio output.
4.7.3
Audio Levels
•
Adjust R64 to get the ‘AF VOLTS’ to ~307mV
±
5mV or –8dBm.
•
Change the monitored audio O/P on the jig to the de-emphasis audio O/P. Tune R58 to
achieve ~307mV
±
5mV or –8dBm.
•
Change the monitored audio O/P on the jig to the flat audio O/P. Tune R66 to achieve
~307mV
±
5mV or –8dBm. Return the jig to monitor the standard balanced O/P.
