LDG AT-1000 Manual - page 12
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The relays operate from an external 12 volt DC power supply. The total current drawn by the AT-1000
depends primarily on the number of energized relays, with the maximum current drain being approximately
1 Amp.
Although the microprocessor’s oscillator runs at 8 MHz, its internal bus speed is on one-fourth that, or 2
MHz. This means that one instruction cycle executes in 0.9 ms. The main tuning routine takes about 75
cycles to make a tuner adjustment and take a new SWR measurement, or 67.5 ms per tuner adjustment. If
running at maximum speed, the microprocessor can try all inductor-capacitor combinations in just 8.8
seconds. Unfortunately, the mechanical relays can’t react as quickly as the microprocessor, and the tuning
speed must be slowed down to compensate for relay settling time.
The tuning routine, written in assembly language, uses an algorithm to minimize the number of tuner
adjustments. The routine first de-energizes the high/low impedance relay if necessary, then individually
steps through the inductors to find a coarse match. With the best inductor selected, the tuner then steps
through the individual capacitors to find the best coarse match. If no match is found, the routine repeats the
coarse tuning with the high/low impedance relay energized. The routine then fine tunes the capacitors and
inductors. The program checks LC combination to see if a 1.5 or lower SWR can be obtained, and stops
when it finds a good match.
The number of tuner adjustments is between 4 and 288. There are 1 to 16 checks for the coarse inductor
tuning, 1 to 16 for the coarse capacitor and between 2 and 256 for the inductor and capacitor fine tuning.
With the speed reduced to 10 ms per selection to compensate for relay settling, the maximum tuning time is
6.1 seconds and the minimum tuning time is 0.06 second. Generally, the farther away from resonance an
antenna is from the exciter’s operating frequency, the longer it takes the tuner to find a match. Test results
show that a 40-meter half-wave dipole tunes to any frequency in the band in less than half a second.