Part 1 LF & MF Communications Equipment Aboard USS Ling (SS-297)
Part 2 LF & MF Communications Equipment Aboard USS Ling (SS-297)
Part 4 LF & MF Communications Equipment Aboard USS Ling (SS-297)
Part 5 LF & MF Communications Equipment Aboard USS Ling (SS-297)
Due to the demise of most maritime operations
on the former international distress and calling frequency by virtue of
OMDSS, there is very little maritime activity below 535 kHz.
Compared
to past years, 500 kHz is eerily quiet. However, given how well we
receive Navtex, there is no doubt that 420-510 kHz would have been
received very well on the RAL.
The
US Navy still uses VLF (in the 16 to 28 kHz region) to broadcast traffic
to subs using very narrow-shift RTTY (on the order of 50 Hz or less).
When 1 was a CW operator in the Navy (NOR and NA W , 1966-1970) we had a
VLF submarine broadcast on 21.6 kHz using a 200 kW output transmitter.
The
VLF range carries quite deep below the salt-water surface (Ed.- This was
known during the WWI era.), but we have no record of the Ling using its
VLF radio while submerged. US Navy VLF broadcast stations use power
levels up into the megawatt range. In recent years, there has
been
a shift to satellite systems, even for subs, using very specialized
equipment. These techniques may soon spell the end for the few remaining
Navy VLF stations.
The
TBL transmitter (serial #127) on the USS Ling was manufactured in 1943
by Westinghouse in Baltimore, MD. This behemoth weighs in at some 700
pounds less power supply, stands six ft tall, and is about 40 inches
wide and about 18 inches deep. Inside this massive housing are two
separate variable frequency master oscillators -one for MF and one for
HF.
The
transmitter covers from 175 to 600 kHz and 2 to 18 MHz in a total of 14
bands. It uses #860 power tetrode tubes for the master oscillator, one
for an intermediate amp covering both ranges, one for an audio
oscillator, which "chops" the RF signal at an audio rate. This
makes the chopped signal audible on any receiver. The chopped signal is
called ICW, or "interrupted continuous-wave" mode, and is
applicable only to the 175-600 kHz range.
The
RF amplifier uses a pair of #803 power pentodes, rated at 150W
dissipation for each tube. The official power rating for the TBL is 200W
output on CW, 100W on ICW, and only 50W on suppressor-grid modulated AM
phone.
According
to documentation found with the boat, RF power output actually ranged
from over 500W CW output at the lower end of its frequency range in CW
mode, to about 75W output on AM phone near the upper end of its range at
18 MHz. The TBL is designed to work directly into the sub's wire
antennas. This submarine has no transmitting equipment for frequencies
below 175 kHz.
The
TBL uses a 50064 external modulator unit to suppressor-grid modulate the
803 RF power amplifier. The 50064 modulator provides transmit-receive
control and just 3W of audio, and weighs 77 pounds! The transmitter can
be accessed on voice locally in the radio room, or from the conning
tower, via telephone handsets which are connected to the modulator and
to the RAK / RAL receiver system.
As
with the RAK and RAL receivers, the TBL transmitter is a testimonial to
battleship construction. The craftsmanship is superb, the controls all
very smooth and solid. Each MO tuning dial is normally freewheeling. The
tuning dials must be manually engaged to change frequency. This was done
to eliminate accidental frequency shift.
Like all the radio equipment, and most other equipment aboard the sub, the TBL is designed to fit through the watertight hatches.
