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TABLE OF CONTENTS CHAPTER SUBJECT PAGE 1 Theory of Operation ........................................................................1-1 Line of Sight .............................................................................1-3 Troposcatter ..............................................................................1-4 Diffraction .................................................................................1-5 Fading .......................................................................................1-7 Diversity Reception ..................................................................1-7 Characteristics of AN/TRC-170 (V)2, 3, 5 ...............................1-9 Service Range of the V2, V3 ....................................................1-10 2 AC Power ..........................................................................................2-1 Power Entry Panel Controls & Indicators .................................2-3 Low Voltage Power Supply #1 .................................................2-11 Low Voltage Power Supply #2 .................................................2-12 AC-AC Converter .....................................................................2-14 3 DC POWER ……………………………………………………….3-1 4 TQG Operation ................................................................................4-1 Fault Indicator Panel .................................................................4-6 Generator Switch Over .............................................................4-10 5 Signal Flow .......................................................................................5-1 Signal Entry Panel #1................................................................5-2 Signal Entry Panel #2................................................................5-3 10 OM-71 Tropo Modem (TM) ...........................................................10-1 Distortion Adaptive Receiver (DAR) .......................................10-4 Receiver Gain Equalization ......................................................10-5 Controls and Indicators .............................................................10-6 Bit Error Rate (BER) ................................................................10-9 TABLE OF CONTENTS (continued) CHAPTER SUBJECT PAGE Circuit Card Description ....................................................................10-13 11 IF Test Panel .....................................................................................11-1 Controls and Indicators .............................................................11-3 12 SN-53 Frequency Synthesizer .........................................................12-1 Controls and Indicators .............................................................12-2 13 AM-7027 Up Converter-Amplifier .................................................13-1 Controls and Indicators .............................................................13-2 14 High Power Amplifier......................................................................14-1 Concept .....................................................................................14-3 Controls and Indicators .............................................................14-5 Tuning the Klystron ..................................................................14-7 High Power Generation.............................................................14-9 BITE ..........................................................................................14-10 a 15 AM-7026 Down Converter-Receiver ..............................................15-1 Controls and Indicators .............................................................15-2 16 ALARM MONITOR and RAAM...................................................16-1 Alarm Monitor ..........................................................................16-2 Antenna Monitor .......................................................................16-8 RAAM Controls and Indicators ................................................16-11 17 Antenna .............................................................................................17-1 18 Orderwires ........................................................................................18-1 DVOW ......................................................................................18-2 ROCU .......................................................................................18-4 AVOW ......................................................................................18-6 19 Loopbacks .........................................................................................19-1 Channel .....................................................................................19-3 Group ........................................................................................19-6 Supergroup ................................................................................19-12 20 Link Establishment ..........................................................................20-1 21 Configurations ..................................................................................21-1 22 Operational Verification .................................................................22-1 APPENDIX SUBJECT PAGE A Cross Reference Guide ....................................................................A-1 B Miscellaneous Information ..............................................................B-1 Baseband Patch Panel ...............................................................B-2 AN/TRC-170 Meter Readings ..................................................B-3 Power Conversion Chart ...........................................................B-5 b Chapter 1 Theory of Operation CHAPTER 1 Theory of Operation ? Dimensionless Variable v = 18.68 r o2 fr r o1 r o2 + o1 fr 1 r o1 r o2 12 f Radius of the first Fresnel Zone = 17.3 R 1 1-1 CECOM LAR Tropo Operation Handbook Basic Theory of Tropospheric Scatter Communications The Earth’s atmosphere is comprised of five layers; Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere. Each layer of the atmosphere affects communication signals differently. The troposphere is the lowest, most dense layer of the atmosphere and extends from the Earth’s surface to an average of 10 km. As you increase height in this layer the temperature drops from 17 to -52 C. Additionally, this is where most of the weather takes place. The tropopause separates the troposphere from the next layer of the Earth’s atmosphere. The troposphere and tropopause together are known as the lower atmosphere. The name troposphere is derived from the Greek tropein, which means to turn or change. With today’s technologies we are able to predict many conditions in the troposphere and use this Figure 1- 1 Atmosphere natural medium to transmit and receive microwave energy. Tropospheric scatter is one method of propagating (transmitting) microwave energy beyond Line of Sight (LOS) or over the horizon. It takes advantage of the refraction and reflection phenomena in the troposphere. Microwave signals are scattered in such a way as to allow reliable communications on hops up to 640 km (400 miles). The Department of Defense uses smaller mobile communication systems to provide battlefield communications. The range of these systems is typically 100-150 miles. There are a number of theories explaining Tropospheric scatter communications ending with a small fraction of the transmitted radio energy being diverted towards a receiving station. One theory is that the diversion is caused by atmospheric air turbulence, irregularities in the refractive index, or similar rapid change in the meteorological elements. This theory accounts for the scattering of radio energy like fog or moisture seems to scatter headlights on a dark night. Another theory is that the air is stratified into discrete layers of varying thickness in the troposphere. The boundaries between these layers become partially reflecting surfaces for radio waves and thereby scatter the waves downward over the horizon. Regardless of the theory you choose to accept, it is undeniable that reliable, effective communications are established using this method. Tropospheric Scatter Communications can be puzzling and frustrating. Once you understand the mechanics of this type of communication system, it is actually simple and easy to work with. There are a number of terms and definitions you should understand to be an effective Tropo Communicator. These terms are explained in the proceeding pages of this chapter. 1-2 Chapter 1 Theory of Operation PROPAGATION: The dictionary defines propagation as; “transmission (esp. sound waves or electromagnetic radiation) through a medium”. The medium in this case is the Troposphere. There are three propagation modes of operation for the AN/TRC-170. These three modes are: LOS, Tropo, and Diffraction, as explained in detail below. Line-Of-Sight (LOS) Figure 1- 2 Line of Sight Ray Path As depicted above, two stations must have a direct ray path between the antennas. Generally, LOS is used no more than 35 miles (57 Km). Substantially less transmit power is required for LOS propagation. The most important factor in LOS communications is the First Fresnel Zone. Figure 1- 3 First Fresnel Zone FIRST FRESNEL ZONE- The transmitted signal from the antenna is not a straight- line. It is actually closer to that of a cone. The Fresnel Zones are an infinite number of signals that are broadcast out of the antenna. The zones vary in signal strength and phase. Fortunately we are only