Ten-Tec 238C manual
Part #74428
First release, June 2009. Printed in U.S.A.
CHAPTER 2
OPERATING INSTRUCTIONS
The following set of instructions will allow
the operator to quickly place the 238C into
operation. Included are descriptions of the
front panel controls and their functions. This
is followed by instructions for antenna
matching and selection, and a brief
discourse on antenna systems matching
theory. Figure 1-1 on the previous page
shows a visual representation of each item
on model 238C and its function or use.
FRONT PANEL CONTROLS
(1) CAPACITOR
This control connects to the variable tuning
capacitor used as one of the elements in the
“L” type matching network. This capacitor
has a tuning range of 40-500 pF and is
continuous tuning with no stops. A marker
system of digits from 0-10 is silk screened in
a 180 degree arc around the top of this
control to make returning to earlier settings
easier and quicker.
(2) INDUCTOR
This control is connected to the roller
inductor, another element in the “L” type
matching network. This inductor has a
tuning range of 0.2-18 uH which is covered
in approximately 30 revolutions of the
control knob. A gear reduction system
behind the front panel of the 238C is
connected to a concentric skirt turns counter
numbered 0-30 in a 180 degree arc over the
top of this control, to make returning to
earlier settings easier and quicker.
(3) IMPEDANCE SWITCH
This 11 position rotary switch is used to
change the configuration of tuning network
for matching either high or low impedance
antenna systems. This switch also selects
additional capacitors as needed for
matching at lower frequencies. When
placed in the 12 o’clock position, the tuner is
connected to the BYPASS configuration and
the network has no effect on the
transmission line systems (antennas are fed
through directly from the transmitter to the
antenna without use of the tuner). The
SWR and power metering remains usable
even when this switch is set to BYPASS.
The purpose of this switch is to set the
capacitor either across the input or across
the antenna, depending on whether a load
of above or below 50 ohms is trying to be
matched (reverses the “L” network).
(4) ANTENNA SELECT KNOB
This 4 position switch is used to select one
of up to four antennas connected to the rear
panel of the 238C and correspond to the
ANT 1, ANT 2, ANT 3, and ANT 4
connectors.
(5) METER
The meter on model 238C is a dual cross-
needle SWR and average or peak-reading
wattmeter. Forward power output is
measured on the right-hand needle, left-
hand scale. Reflected power is read on the
left-hand needle, right-hand scale. SWR is
read by reading the point at which the two
needles cross, on the red scale lines on the
face of the meter. Power output is read in
switchable scales of 200 or 2000 watts.
Peak-reading wattmeter function requires
that 12-15 VDC be connected to the 13.5
VDC rear panel jack. Average power and
SWR can be read even without DC power
connected.
(6) PEAK/AVERAGE SWITCH
This switch is used to select either average
or peak power output reading power on the
238C meter. DC power must be connected
to the rear of the tuner to enable the peak
reading function. Average power can be
read with or without DC power connected.
(7) POWER SCALE SWITCH
The power scale switch is used to set the
power output metering to scales of either
200 or 2000 watts.
