[Lowfer] WC2XSR/13 changes today.

[Ralph Hartwell]

Transmitter off the air at 1145 CDT for antenna measurements.
Transmitter returned to the air at 1541 CDT.

Frequency is 166.500 KC @ 400 watts. Modulation is QRSS30, signing XSR,
followed by a 10 WPM CW ID.

The changes recently made to the antenna system has caused the system
resistance to decrease slightly, and the transmitter is running
excessive drain current. The reflected power was running excessively
high, measuring nearly 100 watts reflected with 500 watts forward power.
It was necessary to add a ferrite core step-down auto-transformer
between the 50 Ohm transmission line and the input to the antenna tuner.

The transformer consists of a single FT-193A-J core with a total of 12
turns of #14 THHN wire. The transmission line connects across the entire
winding, and the input to the antenna tuner is connected to a tap on the
auto-transformer at 16 turns from the ground end of the transformer
winding.

The addition of this auto-transformer has brought the drain current back
down to the design value of 20 amperes @ 26 volts DC input. There is
very little heating noted in the auto-transformer core at the 400 watt
power level under continuous operation. The reflected power has been
reduced to 20 watts with 420 watts forward power, for a VSWR of 1.7:1,
which is within acceptable limits.

RF power is measured with a Bird model 43 wattmeter using a slug which
has been calibrated at 166.5 KC.

The antenna current reads 2.6 amperes, but this may be in error; I will
have to recalibrate the meter and verify this value.

73,

Ralph   W5JGV / WC2XSR / 13

http://home.att.net/~shmrg

http://home.att.net/~ralph.hartwell