MASTR II UHF Receiver Re-Alignment

ICOM Adjustment

freq.gif (8460 bytes)Before you align the receiver, you need to net you receiver ICOM.  ICOM frequency adjustments are made by attaching a frequency counter at the junction of C417 and C415 (shown in the picture to the right, top right corner) which is located to the right of L403. In a UHF receiver the frequency you want to adjust the ICOM to is the receive frequency less 11.2 MHz divided by 3.

An example, if you wished to receive on 447.275 MHz, subtract 11.2 MHz (the IF frequency) and divide by 3.  This results in the frequency you will tune the ICOM, in this case, 145.358333 MHz.

To properly adjust the ICOM frequency, you need to factor in the room temperature and be sure the receiver is at room temperature.

UHF Receiver Re-Alignment

All measurements are against ground (pin 9 of J-601. Use an analog meter or VTVM for all measurements.

Adjust C406 for maximum reading at J601-3.

uhfrec.gif (21550 bytes) Pre-set C411 and C416 in a similar position as C406 then pre-set C306, C307, and C308 fully counterclockwise.

Adjust C411 and C416 for maximum meter reading, then re-tune C406, C411, and C416 for maximum meter reading at J601-4.

Tune C307 and C306 for maximum meter reading at P601-7, then repeat this process.   Next tune C308 for minimum meter reading and re-tune C306 for maximum meter reading.  Do not re-adjust C307 or C308.

Move you meter to J601-1 and apply an on frequency signal to the antenna jack and tune C301 through C305 and  A303 for maximum meter reading.  You can also re-adjust C306, C307 and C308 but not more that 1/4 turn.  Reduce the signal level being feed in to the receiver and repeat as many time as required, reducing the injected signal until no further sensitivity can be obtained.

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