Care And Maintenance - LDG KT-100 Operation Manual

The SWR sensor is a variation of the Bruene circuit. This SWR measuring technique is used
in most dual-meter and direct-reading SWR meters. Slight modifications were made to the circuit
to provide voltages instead of currents for the analog-to-digital converters that provide signals
proportional to the forward and reflected power levels. The single-lead primary through the
center of the sensor transformer provides RF current sampling. Diodes rectify the sample and
provide a DC voltage proportional to RF power. These two voltages are read by the ADCs in the
microprocessor, and are used to compute SWR in real time.
The relays are powered by the 12VDC input provided by the radio interface cable. This
power is supplied by the transceiver itself. The relays are a latching type, and so they consume
no current when not actively switching.
Although the microprocessor's oscillator runs at 20 MHz, which allows the main tuning
routine to execute in only a few milliseconds, the relays require several milliseconds of settling
time for every combination of inductors and capacitors. Thus, it may take several seconds before
all relay combinations are exhausted, in the case of a difficult tune.
The tuning routine uses an algorithm to minimize the number of tuner adjustments. The
routine first de-energizes the high/low impedance relay if necessary, and 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 inductors and capacitors. The program checks LC combinations to see if a 1.5:1 or
lower SWR can be obtained and stops when it finds a good match.
The microprocessor then runs a fine tune routine just after the tuner finds a match of 1.5:1 or
less. This fine tune routine now tries to lower the SWR as low as possible (not just to 1.5); it
takes about half a second to run.
A WORD ABOUT TUNING ETIQUETTE
Be sure to use a vacant frequency when tuning. With today's crowded ham bands, this is
often difficult. However, causing interference to other hams should be avoided as much as
possible. The KT-100's very short tuning cycle, as little as a fraction of a second, minimizes the
impact of tuning transmissions.

CARE AND MAINTENANCE

The KT-100 tuner is essentially maintenance-free. Power limits in this manual should be
strictly adhered to. The outer case may be cleaned as needed with a soft cloth slightly dampened
with household cleaning solution. As with any modern electronic device, the KT-100 can be
damaged by temperature extremes, water, impact, or static discharge. LDG strongly recommends
the use of a good quality ground and properly installed lightning arrestor in the antenna lead.
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