Active and Passive Repeaters

https://books.google.com.pk/books? id=hZX37jfF21EC&pg=PA222&lpg=PA222&dq=active+and+passive+repeater+in+ microwave+link&source=bl&ots=WCSClswnvZ&sig=R42W_6CF7CUeL0pBCVgJExKfb -o&hl=en&sa=X&ved=0ahUKEwjNzp2ejqXOAhXLWxoKHcPC04Q6AEIJTAC#v=onepage&q=active%20and%20passive%20repeater%20in %20microwave%20link&f=false ( Harvey Lehpamer book ) http://telecomfunda.com/forum/showthread.php?29080-Transmission-SystemsDesign-Handbook-for-Wireless-Networks (Harvey Lehpamer book)

https://e68ee56d6120cbd2659fa4a0dfe436d3960b0d11.googledrive.com/host/0B1B HwO0nuhhkUy1BazNtcFpzQ1E/Transmission-Systems-Handbook-Wireless-Networks1580532438-book.pdf transmission system design handbook for wireless networks pdf http://pathloss40.blogspot.com/2009/11/pathloss-40-microwave-repeaters.html

https://en.wikipedia.org/wiki/Passive_repeater

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A typical microwave repeater link setup, this one located near Salt Lake City, Utah,USA(removed in 2013)

Operation principle

Passive repeater in unknown location

A passive repeater or passive radio link deflection, is a reflective or sometimes refractive panel or other object that assists in closing a radio or microwave link, in places where an obstacle in the signal path blocks any direct, line of sight communication. Compared to a microwave radio relay station with active components, a passive repeater is far simpler and needs little maintenance and no on-site electric power. It also does not require additional frequencies, unlike active repeater stations which use different transmit and receive frequencies to prevent feedback. The corresponding disadvantage is that without amplification the returned signal is significantly weaker. Passive radio relay link deflection systems in the vertical level can be realized by receiving the signal with a parabolic antenna and leading it through a waveguide to a second parabolic antenna, where it is radiated. For passive microwave radio relay link deflections in the horizontal plane, flat surfaces of metallic material are used, arranged so that the angle of incoming beam corresponds to the angle of the outcoming signal. The resulting structure resembles a billboard. Similar systems are used also occasionally for TV relay transmitters or as tunnel transmitters. In these cases, a Yagi antennareceives the transmitted signal and supplies it by way of a coaxial cable to a second Yagi antenna.

Microwave System Engineering Using Large Passive Reflectors This paper will provide the microwave engineer with the basic techniques of microwave system engineering using large passive reflectors and will outline the many advantages of their use. Small passive reflectors of the "periscope type" have been used for many years on microwave systems. Large passive reflectors have also been used but to a much lesser degree. Large passives may be used at intermediate points on long (200 miles or more) microwave links in lieu of active repeaters. Most microwave engineers have little knowledge of system engineering using these reflectors. This paper describes their use in both the "near" and "far fields" in line-of-sight systems and describes how they may be used on non-line-of-sight systems (tropospheric scatter and diffraction systems). Formulas are developed and graphs provided which will enable the microwave engineer to determine the path loss of multihop passive reflector systems. Large passive reflectors should be considered as another tool which can be used by the microwave engineer for planning and engineering communications systems. When used effectively with line-of-sight, diffraction and tropospheric scatter modes of propagation, communication systems may be engineered more economically, with more reliability and with a decrease in the operating and maintenance problems.

Passive Repeater Calculations

Passive Repeater Calculations

Q: How do I compute fade margin and reliability for a passive repeater link?

A: You must first determine if the passive repeater is in the �near-field� of one of the terminal antennas. If the passive repeater is in the far-field of both antennas, you must treat the two paths as two independent links. If either the transmitting antenna or the receiving antenna is in the nearfield of the passive radiator you treat the entire system as one link.

The calculated field factor needed for this determination is defined as 1/k

1/k 

__d___

4 A cos(α)

where:

1/k = Field factor (unitless) d

= Distance from the near terminal antenna to the passive reflector in feet

A

= Passive reflector area in square feet

 α

= Wavelength in feet = One-half the horizontal angle include between the two terminals in degrees

If the field factor (1/k) is 2.5 or less, then the passive is in the near field of the terminal. If 1/k is greater than 2.5, the passive is in the far field. The antenna is in the near-field of the passive repeater If the antenna is in the near-field of the passive repeater, the entire circuit encompassing the antenna and passive repeater may be considered as an antenna system. An example of this is the typical �fly-swatter passive� with a reflector (acting as a mirror in a periscope fashion) mounted at 45� to the ground at the top of a tower. It is illuminated by an antenna near ground level looking directly up. In this case it is necessary to determine the gain of that system. The gain is proportional to the projected area of the passive repeater and the efficiency of illumination, and is usually greater than that of the illuminating antenna. A book entitled �Passive Repeater EngineeringManual 161A� showing the equations is available for download here. For more information go to Valmont or contact them via email. They are presently the only known passive reflector manufacturer in the U.S. To use the Microwave Data Base Manager, you consider the system as a single path with the path length equal to the distance from the far terminal to the passive repeater. The antenna gain at the passive end is equal to that of the antenna/passive system gain. A detailed methodology for this calculation can be found in the above referenced text on page 40 in Manual 161A. All other program entries are the same as those of a normal microwave link. The passive repeater is in the far-field of both terminals If the passive repeater is in the far-field of both terminals (1/k> 2.5), it is necessary to assume that there are two independent paths. The gain of the

passive (Gp) is again dependent upon the projected area of the passive and the illumination efficiency. The formula for the gain in dBi is: Gp = 20 log [(4A cosα) /  ]

Using the SoftWright TAP Microwave Data Base Manager, this case is treated as two paths. At the passive repeater end of each path, the gain used is that determined from the above equation. There are no additional losses at the passive end of the circuits since no waveguide or other transmission elements are involved. The transmitted power (EIRP) used for the second path (passive to far end) is equal to the �Received Signal Level� determined in the calculation for the first path (near end to passive). All other parameters entered are those you would normally enter for a two link system. [Thanks to Jim Hart of Hartech, Inc., a Denver area consulting firm and longtime TAP user and Mr. Dennis Beal at Valmont for making this information available.]