Metering Jack Diagram

An analog meter will work fine, provided it is of fairly high input impedance. We always use DMMs. If you have a DMM with a bar-graph display, in addition to the digits, so much the better. The key to using a DMM is to make all adjustments slowly, so you are not subject to the relatively long hysteresis of the meter. You will typically use the 200 mV, 2 V, and 20V scales on your DMM to align the radio.

Most of the measurements on the metering jack are measured against A-, which is accessible at pins 8 and 9 of the metering jack. Metering position G appears to be the exception, and is measured with metering jack pin 5 as the low (-) side and metering jack pin 6 as the high (+) side. This difference rears its ugly head in the VHF-hi exciter, where the GE test set is referenced to A+ rather than A-. We recommend that when aligning VHF exciters, unless you know exactly what you are doing, you place both multimeter leads as indicated in the diagram for reading metering position G. This does not apply to the GE test set.

Connecting to the metering jack itself may involve some creativity. The socket holes are a somewhat inconvenient size. We have used large canvas needles, heavy resistor leads, even brass tacks! Make sure that whatever you stick in there cannot fall out and short something out in the radio.

The diagram above shows the pinout of the metering jack. The letters next to the jack indicate the GE test set measurement position that appears on the adjacent pin. These letters are referenced in the service manuals, not the pin number. A, B, C, D, F, and G appear to be the most commonly used measurements on the MASTR II (based on a quick survey of three service manuals.) In the unlikely event that your manual references E, I, or J, you will need to consult the schematics to see which pin number is used. (Please let me know!)

Most (or all) of the adjustments in a MASTR II are relative, as opposed to absolute. The adjustments involve either peaking or dipping a specific metering jack reading by adjusting one or more controls, usually variable inductors (coils) or variable capacitors.

Peaking an adjustment is relatively straight forward: tune the specified controls to get the largest reading on the meter. You may need to change the voltage range selected on the meter during this process. If you cannot find a peak, it is likely that an earlier stage in the radio is not properly aligned. Back up one or two steps and make sure that the previous stages are correctly aligned.

Dipping can be a bit trickier. The idea here is to find the low reading for the specified controls. Sometimes, the dip will be somewhat shallow. This is usually OK. If you can't find a dip, then backtrack like above.

When aligning transmitters, do not leave the transmitter keyed (transmitting) for an extended period. Connect the meter, key up, make your adjustment, and unkey. It is possible to damage the exciter during tune-up while it is not properly aligned. Be sure a dummy load is connected to the transmitter output during alignment and testing.

• A wattmeter that is accurate at the transmitter frequency
• A dummy load of sufficient power handling capacity to handle the full transmitter output for at least 5 minutes.
• A Signal Generator that can generate a stable signal, with modulation applied, at the receiver frequency.
• Nylon or Delrin alignment tools. Radio Shack sells some of these, but we cannot vouch for them, having never used them. Usually the cheap one suck. You will need one or two sizes of hex-head alignment tools, and a small screwdriver head tool.
• A high-current power supply. You're not going to get 100 watts (or more) of RF if you hook the radio to a 5 or 10 amp power supply. Use a supply that is capable of delivering at least 20 amps continuous duty.
• A Frequency Counter capable of operation at the transmitter frequency.

In addition to all that, a spectrum analyzer is not required, but if you are planning to use your MASTR II as a repeater at a crowded site, it would definitely be a good idea to make sure that the transmitter output is spectrally pure. Operation of a spectrum analyzer is beyond the scope of this document, but whoever owns one will likely know how to use it.