The Ldg Z-100; Trouble Shooting Hints - LDG Z-100 Manual

The LDG Z-100

In 1995 LDG pioneered a new type of automatic antenna tuner. The LDG design uses banks of
fixed capacitors and inductors, switched in and out of the circuit by relays under microprocessor
control. A built-in SWR sensor provides feedback; the microprocessor searches the capacitor and
inductor banks, seeking the lowest possible SWR. The tuner is a "Switched L" network consisting
of series inductors and parallel capacitors. LDG chose the L network for its minimum number of
parts and its ability to tune unbalanced loads, such as coax-fed dipoles, verticals, Yagis; in fact,
virtually any coax-fed antenna. The inductors are switched in and out of the circuit by relays
controlled by the microprocessor. An additional relay switches between high and low impedance
ranges.
The capacitors are connected to ground with the seven inductor relays. Another relay switches the
entire capacitor bank to the input or output side of the inductor. This switching allows the Z-100
to automatically handle loads that are greater than 50 ohms (high setting) and less than 50 ohms
(low setting). All of the relays are DPDT type sized to handle up to 125 watts continuously.
The relays operate from DC supplied by via the power input jack. The total current drawn by the
Z-100 depends primarily on the number of energized relays, with the maximum current drain
being approximately 300 mA, but only during the few seconds a tuning cycle is running. At all
other times, the tuner is in a "deep sleep" mode drawing nearly zero current. The latching relays
retain the tuned setting indefinitely, even when power is removed. The last tuned setting will still
be set on the next power-up.
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 microprocessor runs a fine tune routine just after the tuner finds a match at an SWR of 1.5 or
less. This routine tries to get the SWR as low as possible (not just 1.5); it takes about a half
second to run. There is also a quick tune mode. If the swr is below 2.0 when you press the tune
button to start a tuning cycle, the tuner will first run the fine tune routine to see if it can achieve a
low swr without a complete re-tune. This also takes about a half second to run. If it does not find
a good match, then it runs the main tuning routine.
The memory mode checks the memories first, then runs the main tuning routine if needed.

Trouble shooting hints

Power levels: Always use the lowest RF power setting as possible. It reduces interference and
problems caused by stray RF. While the Reset function can be used at any time, if you have
problems, try it with no RF present.
Getting the lowest SWR: In some cases, the tuner may not find an acceptable match. Once trick
that be used is to tune off the desired frequency by 25 or 50 KHz, tune, then move back without
re-tuning.
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