Align VHF Receiver

MASTR II VHF 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 VHF receiver the frequency you want to adjust the ICOM to is your receive frequency less 11.2 MHz which should be 9 times the crystal frequency.

An example, if you wished to receive on 147.99 MHz, subtract 11.2 MHz (the IF frequency) which yields 136.79 MHz. Adjust the ICOM for a frequency reading measured at the indicated test point. The crystal frequency should be the receive frequency less 11.2 divided by 9. For a receive frequency of 147.99 MHz the crystal frequency should be 15.19888 MHz.

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

receiver.jpg (89647 bytes)

All measurements are against ground (pin 8 of J-601. Use an analog meter or VTVM for all measurements.

	Adjust L401 for maximum meter reading at J601-3.
	Preset L402 and L403 to a position similar to L401, then preset C306 and C307 fully counter-clockwise.
	Adjust L402 and L403 for maximum meter reading on J601-4, then re-tune L401, L402 and L403.
	Carefully adjust C306 for minimum then adjust C307 for maximum.
	Attach your meter to J601-1 and apply an on frequency signal to the antenna jack. Adjust the signal strength as needed during the alignment.
	Adjust C501, C301, C302, C303, C304, C305 (and T2301 if present) for maximum meter reading. Reduce your signal strength and re-tune slightly.
	C306 and C307 may be adjusted no more than a quarter turn for best quieting.