Detailed Circuit Analysis: Pc-1000B; Impedance Transformers; Tuner - SAC SS-800AVS Manual

3.2 DETAILED CIRCUIT ANALYSIS: PC-1000B
3.2.1 Impedance Transformers:
The impedance transformer is bifilar wound on a ferrite toroid.
The secondary has ii taps and is designed to transform a secondary
load between 2 and 25 ohms to a 50 ohm input impedance. Tap selection
is made with a switch on the front panel of the coupler. An air
core transformer connected to the low potential end of the impedance
transformer secondary samples the antenna current to provide a
signal for the Antenna Current Meter.
3.2.2 Tuner:
This 240 turn coil has a transformer coupled shorted ring that can
be turned manually or by the autotune motor. The 44 turns physically
below the tuning ring are tapped every 4 turns for a fine tuning
adjustment. The 200 turns above the tuning ring are tapped at 5
turns, i0 turns~ ~20 turns, and thereafter in 20 turn steps, to the
top of the coil. The upper tap selection is made with a solder
connection behind a removable panel. The lower tap selection is
made with a switch on the front panel.
The autotune system automatically turns the tuning ring in a direction
to tune the antenna system. If the correct taps have been chosen,
the ring will stop when the system is tuned and change automatically
when the system detunes due to changes in the antenna environment.
If the correct tap has not been chosen, the tuning ring will move
to a MAX or MIN limit and an LED indicator on the coupler front
panel will indicate whether more or less inductance is needed. A
manual knob for the tuning ring is also available on the coupler
front panel. The tuning ring is capable of varying the total
inductance approximately ±5% depending on the combination of taps.
Maximum inductance with the full coil is 3.5 mH ±130 uH. Minimum
inductance is 25 uH ±3 uH. This is sufficient to tune a 200 to
1500 pF antenna from 190 KHz to 625 KHz. Tables are given showing
the tuning range for SAC's Mast Antenna, Guyed Mast Antenna, and
Symmetrical "T" Antenna.
SS-800AVS Southern Avionics
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