HF Facsimile Recorders
As a weather observer, you may be tasked to copy
HF facsimile products by using miniaturized facsimile
(minifax) recorders.
Normally, several different
frequencies are available for each HF broadcast station.
A few of these frequencies are available 24 hours per
day. You must monitor the signal to ensure that usable
quality graphics are produced. Due to daily changes in
atmospheric conditions, you will find that lower
broadcast frequencies provide a better signal at night,
while higher broadcast frequencies provide a better
signal during the day.
Most U.S. originated HF radio analog signal
facsimile transmissions include a marking tone at the
beginning of each line of the image. This marking tone
is automatically interpreted by the recorder to indicate a
new line of image, and the recorder automatically aligns
each line properly to form the image. Some foreign
facsimile transmissions do not contain a recognizable
marking tone, which results in a skewed image where
each line of the image is offset an inch or two to the right
or left. Manually setting the recorder LPM-setting to
match the transmission LPM setting normally corrects
the skew. Common settings used are 60-, 90-, 120-, or
240-lines-per-minute.
Two models of minifax’s are in use by Navy MET
and Marine Corps METMF units: the 9315 series TR4
and the TRT models. Both are equipped with a 5-foot
whip antenna and preamplifier for use aboard ship or
ashore. Aboard ship, the ship’s antenna system may be
connected to the recorder instead of the 5-foot whip.
The Alden 9315 series facsimile receiver/recorders
contain a digital receiver and use dry, thermally
sensitive 1 l-inch-wide rolls of paper. Replacement
rolls of paper are inserted through the top of the
equipment following instructions provided inside the
paper compartment. A forward and reverse scanning
thermal print head is used instead of a stylus on a belt.
You must be very careful when feeding the paper
through the roller system to avoid damaging the thermal
print head.
ALDEN 9315 TR4.—This minifax is widely used
by mobile teams. The TR4 model can copy facsimile
transmissions received over the internal receiver, over
an external radio, or over the telephone. AM voice
broadcasts and CW may be monitored on a speaker. A
9315 TR4 is shown in figure l-20.
ALDEN 9315 TRT.—Although the TRT model
looks nearly identical to the TR4 model, it is much more
than a facsimile receiver/recorder. The 9315 TRT has a
Figure 1-20.—Alden 9315 series TR4 model facsimile receiver/recorder.
l-36
