AT-784_antenna_serv_user_TM11-5985-284-15_1967.pdf

TM 11-5985-284-15 D E P A R T M E N T O F T H E A R M Y T E C H N I C A L M A N U A L OPERATOR, ORGANIZATIONAL, DS, GS, AND DEPOT MAINTENANCE INCLUDING REPAIR PARTS SPECIAL TOOLS LISTS MANUAL ANTENNA, LOOP AT-784/PRC ( N S N 5 8 2 0 - 0 0 - 0 8 6 - 7 6 5 1 ) This copy is a reprint which includes current pages from Changes 1 through 5. Title was changed by Change 5. H E A D Q U A R T E R S , D E P A R T M E N T O F T H E A R M Y F E B R U A R Y 1 9 6 7 CONDENSED OPERATING INSTRUCTIONS Cautioa: Use for reception oniy. Do not transmit. Whenever loop antenna is not in use, keep ATTENUATOR switch set in O position. Choose operating location free from obstructions. To Operate u. From .Iiodtflutcd Carrier tli(al Sowcc.The nuru- bers of steps 1 through 3 and 8 belov nre the same as those on the illustration. ( 1 ) Swing loop antwma up from the case. Do not extend the whip. (2) Connect imtennu cable from connettor jl (of AT10t32/PRC ) to the tintenna coaxial connector of the receiver. Set reiver viunle rontrol to (3) (4) (3) 6) muxirnurm and squelch off. Set the ATTENl.TOR s!vitcb to positio) 0. Set the BAN IMIWITCH to the desired frequency band. Adjust FISE TSE (mntrf)l to fiesi!w! operating frequency within elftwl 1,:11)(1. Hold 100IJ antwna ut eye ievel tiltl rottite ujtil signal is received. Adjust FIXE TUNE (5) for maximum reeponee. If resporme is too fstrOUg, advance A!IYENUATOR (3) to htgher number. ( 7 ) Rotating the loop will obtain two Poait!on% 180” apart corresponding to SIGNAL NULL arrows, giving maximum signal response. ( fiJ Extend the whip and note signal reaponae in one position. Rotate the antenna one-haM turn ( 160 ) and note response in second position. (0) Orient the antenna to obtain stronger signal reslmuse. The SIGNAL MAX arrow (on the case) now points toward the transmitter. ( 10) Retract the whip. Rotate the antenna one- quarter turn (60” ) to SIGNAL NULL position for sharp and accurate bearing Indication. h From Unmodulated Carrier Signal 8our however, one of similar type is requiredfor use of this antenna. F o r example: Radio Set AN/PRC-25, which is a manpack receiver-transmitter, is capable of receiving input signals over the frequency range of 30 to 76 MHz. 1 - 5 INSTALLATION CHAPTER 2 AND OPERATION C 2, TM 11-5985-284-15 INSTRUCTIONS Section I. SERVICE UPON RECEIPT OF ANTENNA LOOK AT-784/PRC 2-1. Unpacking a. Packaging Data. When packed for ship- ment, the components comprising Antenna, Loop AT-784/PRC, are placed in a corrugated cardboard carton. A typical shipping carton and its contents is shown in figure 2-1. The dimensions of the carton are 10 by 6 by 5 inches. b. Removing Contents. To unpack, proceed as follows: Open the carton, lift out Bag, Cot- ton Duck CW-445/PRC, remove its contents, and check the components (para 2-2, and para 1-6.1). NOTE Save the original packing carton. It can be used again when the equip- ment is repacked for storage or shipment. 2-2. Checking Unpacked Equipment a. Inspect all equipment for damage possi- bly incurred during shipment. If the equip- ment has been damaged, report the damage on DD Form 6 (para 1-3b). b. See that the equipment is complete as listed on the packing slip, or paragraph 1-6.1. Report all discrepancies in accordance with AR 735-11-2. Shortage of a minor assembly or part that does not affect proper functioning of the AT-1082/PRC should not prevent use of the equipment. 2-3. Installation To install Antenna AT-1082/PRC, follow the procedures in a through e below. a. Remove the AT-1082/PRC from the CW-445/PRC (carrying bag). Figure 2-1. Packaging of Antenna, Loop AT-784/PRC. 2-1 C2, TM 11-5985-284-15 b. Place the loop antenna into operating position as shown in figure 2-3. c. Connectconnector J1ofthe AT-1082/PRC to the antenna coaxial connec- tor of the radio set with which it is to be used by the CG-3344/PRC cable. The 12-foot cable (CG-2840A/U) may be added to the CG-3344/PRC to increase the interconnection cable length, if required. d. Remove all other antennas from the radio. e. Theshieldcapattached tothe CG-3344/PRC (fig. 1-1) is provided for use with Receiver-Transmitters, Radio RT-505/ PRC-25 (part of Radio Sets AN/PRC-25 and AN/VRC-53) and RT-841/PRC-77 (part of Radio Set AN/PRC-77). On these receiver- transmitters, press the shield cap down as far as it will go over the whip antenna base. The inside top of the shield cap should contact the top of the whip antenna base on the radio and ground it to the radio set chassis. When the radio set whip antenna base is not grounded, it interferes with homing signals. 2-4. Siting (fig. 2-2) The best performance of Antenna AT-1082/ PRC is obtained when it is used over an unob- structed line-of-sight path with a compatible radio set. For this reason, the AT-1082/PRC should be operated away from obstructions such as large buildings, bridges, steel struc- tures, and hills. These objects will block or deflect the desired signal, thereby making homing difficult or impossible. Also, this equipment should not be operated near high-power or telephone lines. The best sites for desired directional looping are on hilltops or over open, flat terrain. Figure 2-2 illus- trates typical good and poor locations for AT-1082/PRC operation. 2-2 TM 11-5985-284-15 Figure 2-2. Using AT-1082/PRC in good and bad operating areas. 2-3 Figure 2-3. TM 11-5985-284-15 Section Il. ANTENNA CONTROLS 2-5. Controls and Their Uses All operating controls of Antenna AT-1082/ PRC are listed in paragraph 2-6 and are Shown in figure 2-3. Care should be taken not to force controls since damage to switch contacts may result. 2-6. Controls and Antennas 2-4 Control or antenna Loop antenna - - - - - - - Function When extended, receives radio waves for transmission through the AT- 1082/PRC to the associated receiver. When situated broadside to the transmitted signal, the signal is attenuated (null condition); con- versely, when situated so that the edges of the loop face the trans- mitted signal, the signal is not attenuated. Control or antenna Sense whip antenna. TM 11-5985-284-15 Function When extended and in conjunction with the loop antenna having the opposite edge of the loop an- tenna facing the transmitted signal, de-termines (senses) the direc- tion from which the signal is transmitted. Section Ill. OPERATION UNDER USUAL CONDITIONS Caution 1: Use the AT-784/PRC for recep- tion only. Do not transmit when the AT-784/ PRC is connected to the radio set; remove all other antennas from the radio set. Caution 2: Keep the ATTENUATOR switch to O whenever the AT-1082/PRC is not in use. 2-7. General a. Modulated and Unmodulated Carrier.Di- rection finding of, or homing-in on, a transmitting station is accomplished by detecting its modulated or unmodulated carrier. Usually, it is better to home-in on the unmodulated carrier signal than a voice or test tone; the test tone or voice is best used when the transmitting signal is somewhat distant from the AT-1082/PRC. When the transmitting site is nearby, with the carrier modulated or un- modulated, it is better to follow the carrier indica- tion rather than the modulation feature. (1) Modulated carrier. Modulation of the transmitter carrier frequency occurs when voice, music, test tone, etc., are trans- mitted. (2) Unmodulated carrier. This action oc- curs when the transmitter is turned on but the carrier frequency is not modulated by voice, music, test tone, etc. On ampli- tude modulation transmission (am), the transmitter is detected by the quieting of the noise when tile receiver is turned in the area of the transmitter frequency. On frequency modulation (fm) trans- mission, the transmitter is detected by the lessening or stopping of the rushing noise when the receiver is tuned to the area of tile transmitter frequency. b. Maximum Signal.The terms maximum signal and maximum are used to define the posi- tion of the loop antenna. when it is so oriented that the greatest signal response (maximum signal) is heard in the receiver. This occurs when the sense whip antenna is extended for sensing (d below). At this time, a greater response is obtained on the receiver when that edge of the loop antenna op- posite the edge in which the sense whip antenna is mounted faces the transmitter.When the sense whip antenna is retracted, signals of equal inten- sity are obtained from either edge of the loop antenna. c. Null Signal.The terms null position and null are used to define tile position in which the loop antenna is oriented when minimum or no sig- nal response is heard on the receiver. This occurs when either broadside of the loop antenna is facing the transmitting station. The two nulls are de- fined properly when the sense whip antenna is re- tracted.The null gives a sharper or more ac- curate indication than the maximum sense position (d below). Consider the loop antenna as an en- larged gun-sighting device; it is necessary to look through the hole formed by the loop antenna to- ward the transmitting station. This will be the same direction as the maximum signal from the edge of the loop antenna (d below). In the pres- ence of a strong signal, the null will be more clearly defined and quite narrow; the rotation of a few degrees will produce sharp variations in the received signal. On a weaker signal, the width 2-5 TM 11-5985-284-15 of the null may increase to 30 or 40 O. The center of the null (or area) is the correct bearing. d. Sensing.Because there are two nulls, the null indication does not provide sufficient informa- tion for the operator to determine whether the transmitting source is in front of, or behind, the loop antenna. To find the actual direction of the transmitting source, a null is detected, the sense whip antenna is extended, and the loop antenna is turned sidewaysto the transmitting signal. When the signal is loudest in the receiver, the SIGNAL MAX arrow on the top of the case (fig. 2-3) will point in the direction of (sense) the transmitting signal. e. Homing. Homing is the procedure of detect- ing a transmitting station and approaching it. The general procedure is as follows: (1) (2) (3) (4) Find the null. Determine the sense and take a bearing on the transmitting station as indicated by the SIGNAL MAX arrow on the top of the case (fig. 2-3). When the direction of the transmitting station is determined, the sense whip an- tenna is retracted, the loop antenna is turned broadside to the transmitting sta- tion, and the null indication is detected on the receiver.If the null is particularly broad, rotate the loop antenna back and forth a few times. Select the center of the null, and proceed on a line through the center of the null until the transmit- ting station is reached. As the transmitter is approached, succes- sive bearings can be taken with increased accuracy because of the narrowing null area which results from increased signal strength. f. Attenuation. Caution: Whenever the loop antenna is not in use, keep the ATTENUATOR switch at 0. (1) 2-6 Very strong signals may have a tendency to obscure the null and sense indication. In general, such signals will be found close to the transmitter.If the hearings are obscured and the transmitter cannot be seen, advance the ATTENUATOR switch to position 1, 2, 3, or 4 to reduce the signal strength to the point, where the null becomes clear. (2) Positions 1, 2, 3, and 4 provide increas- ing and marked differences in attenua- tion. The position of least attenuation that permits sense and bearing determi- nation should be used.operation in ATTENUATOR position 4 is not nor- mally used except in the immediate vicin- ity of the transmitting station (within 100 to 200 yards depending on the ter- rain).An accurate sense indication will be difficult, to obtain in this position, but this condition should not present any operating difficulties since the general di- rection of travel has been previously established and the null bearing should be sufficient for transmitter location. 2-8. Operation The operating procedure of Antenna AT-1082/ PRC for homing-in on a modulated or unmodu- lated carrier is described below.On the receiver, the greatest, signal response (maximum signal) for a modulated carrier is indicated by a loud audio output ;for an unmodulated carrier, the indication is indicated by maximum receiver quieting. a. Preliminary. (1) Check to see that the AT-1082/PRC is (2) connected to the receiver (para 2-3). Remove all other antennas from the re- ceiver.Set the ATTENUATOR con- trol to 0. On the receiver, tune to the operating frequency, set the volume control for maximum loudness, and set the squelch control to off when there is such a provision. b. Procedure. (1) Unfold the loop antenna, and set the (2) BANDSWITCH and FINE TUNE con- trols to the positions that are closest to the frequency setting on the receiver. For example, to tune to 45.80 MHz, set the BANDSWITCH control to 40 and the FINE TUNE control to 5. Hold the AT-1082/PRC vertically (fig. 2-2), and rotate it clockwise and counter- clockwise for maximum signal indication on the receiver.Readjust the FINE fig. 2-2 (3) (4: TUNE control for a greater output sig- nal on the receiver. A maximum signal indication will be indicated by a loud(b) audio output on the receiver because of a modulated carrier or by maximum re- ceiver quieting because of an unmodu- lated carrier. Caution: Do not use the FINE TUNE control setting as a standard in determiningthe transmitter fre- quency. Adjust the ATTENUATOR control for comfortable audio output from the re- ceiver. At this point, the AT-1082/PRC loop antenna is oriented edgewise to the transmitting source. To determine the direction of the signal source, proceed as follows:(5) (a) Rotate the loop antenna 90 to obtain a null indication on the receiver. The loop antenna is now broadside to the(6) signal source and is indicated by the SIGNAL NULL arrows on the signal 2-9. General TM 11-5985-284-15 direction label on top of the case (fig. 2-3). Extend the sense whip antenna. This action will cause a signal output from the receiver. Starting with the broad- side position ( (a) above), listen for the maximum output signal while rotating the loop antenna clockwise and then counterclockwise from the broadside position. Set the AT-1082/PRC to the position that provides the strongest signal indication in the receiver. The loop antenna is again in line with the transmitting signal source, and the sig- nal source is in the direction away from the sense whip antenna, as indicated by the SIGNAL MAX arrow on the signal direction label. (* See below.) Retract the sense whip antenna, and, using the loop antenna, home-in on the signal source with the null indication. Adjust the ATTENUATOR control for a comfortable listening level of the re- ceived signal. Section IV. OPERATION UNDER UNUSUAL CONDITIONS Operation of Antenna AT-1082/PRC may be difficult in regions where extreme cold, heat, hu- midity and moisture, sand conditions, etc., pre- vail. In paragrap