HF Facsimile Recorders

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