NHRC MASTR II InfoSite -- VHF MASTR II Alignment Instructions

These instructions describe alignment of the RF assembly of the VHF MASTR II receiver. The IF and Mixer alignment is not included; it rarely needs to be performed.

Some older receivers will not have the three trimmer capacitors (C406, C411, and C416) on the Oscillator/Multiplier board, they will have three inductors (L401, L402, and L403, from front to rear) with tunable slugs instead. Follow the directions as shown, but adjust L401 instead of C406, L402 instead of C411, and L403 instead of C411.

VHF Receiver Alignment
Step	Receiver Metering Jack Pin #	Test Set Position	Instructions
1	3	C	Peak C406. Set C411 and C416 in a similar position. Set C306 and C307 fully CCW.
2	4	D	Peak C411, then peak C416. Peak C406, C411, then C416. Dip C306 and then peak C307.
3	2	A	Inject a signal on the receiver's frequency into the hole adjacent to C305. Adjust the signal level for a meter reading of approximately 0.38 volts.
4	1	B	Leaving signal injected at same level as step 3, peak C502.
5	1	B	Inject a signal on the receiver's frequency into the hole adjacent to C304. Adjust the signal level for a slightly noisy signal. Then, peak C305. You may need to reduce the signal generator level one or more times to keep the received signal slightly noisy. Alternately reduce the generator level and peak C305 to obtain the largest peak meter indication with the lowest signal generator level.
6	1	B	Inject a signal on the receiver's frequency into the hole adjacent to C303. Adjust the signal level for a slightly noisy signal. Then, peak C304. Use the same method as step 5 to obtain the largest peak meter indication with the lowest signal generator level.
7	1	B	Inject a signal on the receiver's frequency into the hole adjacent to C302. Peak C303 as above.
8	1	B	Inject a signal on the receiver's frequency into the hole adjacent to C302. Peak C303 as above.
9	1	B	Inject a signal on the receiver's frequency into antenna jack. Peak C301 and C302 as above. If the UHS preamplifier is present, peak transformer on that.
10	1	B	Leave signal injected on receiver's frequency into antenna jack. Carefully tune C502, C301, C302, C303, C304, and C305 for peak indication and best sensitivity. A signal-to-noise analyzer can be helpful here. Continue to tweak these controls several times until no further improvement in sensitivity can be made.

Mixer and IF alignment is almost never required. Do not attempt to align the mixer or IF stages of the receiver without at least a signal-to-noise analyzer.

The frequency of the receiver ICOM can be adjusted by turning the trimmer capacitor on the top of the ICOM. The frequency can be measured directly with a frequency counter connected to the junction of C418 and C419 on the Oscillator/Multiplier board (frequency here should be receive frequency - 11.2 MHz) or the ICOM's frequency can be adjusted by injecting a signal into the receiver from a known reliable source (signal generator or service monitor) and tuning the ICOM for best receive sensitivity.

VHF Transmitter Alignment
Step	Metering Jack Pin #	Test Set Position	Instructions
1	2 (exciter)	A	Peak T101.
2	1 (exciter)	B	Peak T102 and T103.
3	3 (exciter)	C	Dip T104.
4	4 (exciter)	D	Peak T105. Peak T104. Dip T106.
5	7 (exciter)	F	Peak T107. Peak T106. Dip T108. Peak T109.
6	5 - 6 + (exciter)	G	Note:Move multimeter to 5/- and 6/+ Peak T110. Peak T108. Peak T109.
7	4 (PA)	D	Meter is now on PA metering jack. Peak T111 and T112.
8	5 (exciter)	G	Meter is now on exciter metering jack. Note:Move multimeter to 5/- and 6/+ Peak T108. Peak T109. Peak T110.
9	4 (PA)	D	Meter is now on PA metering jack. Peak T111 and T112.
10	Wattmeter		Adjust power control potentiometer on Power Amplifier for desired output power.

Use a frequency counter or service monitor to adjust the transmitter ICOM. The trimmer capacitor on the top of the ICOM adjusts the ICOM's frequency, and therefore the transmitter's output frequency.

Transmitter maximum deviation is set with R104. Note that this control adjusts the deviation level after the limiter. This control should be adjusted to ensure that maximum deviation does not exceed 5.0 KHz. A service monitor or deviation meter is required to make this adjustment. If you do not have the required test equipment, then don't adjust the deviation control, it's probably fine right where it is.

When setting power level, do not exceed rated output power. If the radio will be used as a repeater, or in any other similar high-duty-cycle application, then the maximum output power should be derated to 1/2 to 2/3 of the specified rated output power.