Section 3
GENERAL ALIGNMENT INSTRUCTIONS
This section describes the alignment procedures for various radios. Listed below are the methods used to align the various radio circuits. The following pages indicate coil locations and part designations (L18, C4, etc.) for individual radios.
The following alignment must be performed after all installations.

VCO ALIGNMENT
NOTE: Use a non-metallic alignment tool GC9440 or equivalent.
1. Scan the 400 to the upper limit, 28.000.
2. Turn the VCO adjustment to a point where the radio is near 27.950. The first digit on the 400 will display an L, indicating the PLL synthesizer is out of lock.
3. Align the VCO adjustment until the radio just locks on 28.000 MHz. Do not turn the adjustment past this point as it can make other adjustments more difficult. The first digit on the 400 will now show a full 2 indicating the PLL is locked.

DOWN MIXER ALIGNMENT
1. Connect an oscilloscope (5 MHz or better vertical amplifier frequency response) to TP-3 (inside the 4000. Adjust the scope triggering to give a stable trace.
2. Align L18 for maximum output without double peaking. Check for correct alignment throughout the band.

Fig. 23 - Down Mixer Waveforms

LOOP FILTERING ALIGNMENT
There are many schools of thought on loop filtering-alignment but the best procedure is to listen to the radio. The loop filter is aligned for best SSB clarity. The radio must be tested on several frequencies to insure correct alignment.

Most radios will require 300-700 ohm resistance for the trimpot 8100. If the resistance of the trimpot is too low, the radio will warble (a byproduct of FM) on higher frequencies, 27.800 range. Should the trimpot have too much resistance the radio will lose selectivity (splatter or bleedover) on lower frequencies, 26.600 range.

The loop filtering can make orbreak an otherwise good 400 installation. Loop filtering adjustments are critical for a clean-sounding radio.