microwave RF repeater faqs
microwave RF repeater answers
A.1 Yes, the higher capacity repeaters can handle 155.52 Mb/s traffic / OC3 / Sonet / ATM rates. Peninsula RF Repeaters are designed to support the available bandwidths and capacities in each microwave radio communications band. Please see Engineering Note 650-1001-01 for more detailed information.
A.2 The RMAS-120 receiver can interface to the terminal manufacturers alarm unit (i.e. Alcatel MCS-11 Alarm or others ) point by point inputs at the MW terminal location. The RMAS-120 transmitter is located at the repeater site and transmits the condition of the repeater to the RMAS-120 receiver unit. The RMAS-120 receiver unit's outputs are tied into the terminal radio or site alarm panel.
A.3 Passive Repeaters ( Billboard Reflector ), due to their large surface area they are prone to be shifted out of alignment due to winds and requires realignment (causing outages or degraded performance)
Billboard systems have a very large footprint and typically causes
major concerns over the way it looks, with neighbors and planning commisions.
Passives are prone to multipath if the area behind the billboard is not clear sky. MW signals can reflect off the hillside behind the passive and cause multipath problems. RF Repeaters have been shown to reduce this problem significantly (50 dB improvement in C/I).
Passives can suffer from decoupling fades, especially over 6GHz. When the terminal antenna is large, as needed for a successful passive, the beam width is very small, 0.5 ~ 0.9 degrees. Atmospherics may cause the beam to shift position and not illuminate the passive fully or at all. This "decoupling" of the beam causes severe fading because less beam energy is reflected.
Beamwidth of the signal exiting a passive reflector is extremely narrow, 0.1 ~ 0.2 degrees. This narrow beam is difficult to aim and if the passive alignment shifts, the beam may miss the terminal. Another form of decoupling fade.
MW RF Repeaters avoid decoupling fades by using more standard sized antennas with somewhat wider beamwidths.
MW RF Repeaters have been used in a number of locations that were otherwise suitable for passive reflectors because the RF Repeater took up less space, offered less of an objectionable view in sensitive areas (National Parks, National Forests).
Passive reflectors work best when one path is quite short and the other is longer. MW RF Repeaters are not limited in this way and perform well especially at mid-path locations.
Microwave RF Repeaters can operate over much longer paths than passive reflectors. Microwave RF Repeater paths are in many cases as long as terminal to terminal paths.
A.4 Most customers use the remote monitoring alarm system (RMAS-120) as the terminal radios only report total failure. The RMAS-120 can provide a suite of in-service monitoring points (31 alarm points ‚ 27 digital & 4 analog with 8 uncommitted alarm points available for customer interface)
A.5 Repeaters are stand alone units. 12 Volt units are easier and less expensive to use with solar power. Repeaters have very low power consumption and are excellent in solar power applications.
An exception to using 12 Volts is the RF-11000. The RF-11000 has a greater load and was designed for 24 Volts. The greater battery voltage reduces the current in half. At the lower current, less voltage is lost in the wiring.
24 VDC battery operation is available as an option for many of the "12V" repeaters.
A.6 Yes, they have the same licensing requirements in the United States as terminal radios. See each model spec sheet for FCC ID Number.
A.7 The "equalizer" corrects for the filter group delay and some amplitude roll off. It does not compensate for propagation channel variations such as an adaptive equalizer does. These are fixed tuned complementary to the filter delay shape.
A.8 Delay equalization is available in the bands that carry higher traffic. Delay equalization is available in the following repeater bands: 2 GHz, 4 GHz, 6 GHz, 7 GHz, 8 GHz, 11 GHz
A.9 The amplifiers in the repeaters are linear class A and are a complete subsystem with Automatic Level Control (ALC), Modulation, Redundancy, LNA, and HPA features. The input LNA sections have a low noise figure typically near 3 dB when operating at maximum gain.
A.10 The power setting per modulation type is quite firm but with some small margin just to keep the majority of radios operating at BER 10E-12 (Bit Error Rate) or better at normal RSL (Receive Signal Level). Radios with FEC (Forward Error Correction) will normally run error free through the repeater at spec power level. We have seen radios with excellent FEC be able to work great through the repeaters at even higher power settings, perhaps as much as 6 dB greater than spec.
The upfade reserve is nominally 5 dB and this is a true AGC type control so there is no noticeable distortion until all the AGC attenuation is in. The 5 dB upfade number is a guaranteed number from nominal, typically there may be more upside AGC gain reduction possible. So, on a strong upfade, amplifier distortion will start building up somewhere over the 5 dB upfade number or when all the attenuation is in. How the radio link performs is also dependant on the terminal radio error performance. FEC helps enormously.
The actual amount of upfade reserve is dependent on the particular hop configuration, radio Tx power, net path loss, etc. We try to design toward the nominal input as this will leave about 10~15 dB AGC in for downfade (the gain can increase 10~15 dB to offset the downfade). In the designs, when the calculated input level is strong enough to reach the 5 dB upfade AGC reserve point, we will recommend adding fixed input attenuators so as not to exceed this input level limit.
A.11 For short feeders with an air volume up to 2 cubic feet, static desiccators (Andrew SD-002A, SD-003) are recommended (1 ea per 1 cubic FT up to 2 each per feeder). For feeders with volume over 2 cubic FT, pressurization by dry nitrogen (pressure tank/bottle) or an electric pump dehydrator is recommended (consider the available power, DC dehydrators are available for operation from the solar array). The repeater W/G ports should be fitted with a pressure window. The repeater is quite pressure tight but not completely due to the many flange joints inside. The RMAS-120 Alarm system optionally includes a pressure sensor that can be connected to the pressurization manifold. When pressure drops below about 1 PSI, a "Low W/G Pressure" alarm is reported.
A.12 Frequency Diversity is implemented in the RF repeaters by providing filter and amplifier sets for each microwave carrier frequency. The filters are arranged in a standard branching manifold to route each MW carrier frequency to or from it's dedicated amplifier. Like SD, the switching or combining takes place at the terminal radios. FD is best used in a long path - short path situation but will provide substantial improvement in a long path - long path situation as well.
A.13 Space Diversity can be implemented at the RF Repeater only on a long path (requiring Space Diversity improvement on one side of the repeater) and short path (steady, almost no fades on the other side) basis. Two "channels" are sent from the repeater to the short end radio. Switching or combining is done at the terminal radio at the short path end between the two "channels". The channels can be either cross polarized same frequency or two frequencies as in FD.
Space Diversity receive can always be implemented at the microwave radio terminals. SD receive is often used to balance the link performance from the lower powered RF repeater to the MW radio receivers.
Space and Frequency Diversity, also known as Hybrid Diversity is a powerful anti-fading tool. SFD is implemented with Frequency Diversity RF repeaters configured with 3 or 4 antenna ports thus supporting Space Diversity antenna arrangement on one path or on both paths.
A.14 Remote repeater monitoring is achieved by transmitting the alarm telemetry on one or more microwave carriers passing through the RF repeater.
The 16 b/s, 32-baud serial data stream can be fed to all or selected amplifiers equipped. Inside each amplifier, an amplitude modulator imposes a 1 dB Peak-to-Peak carrier variation at about 32 Hz. The terminal radio receiver’s AGC circuit detects this modulation. The AGC loop senses the modulation as fast fading since the modulation frequency is within that range. The AGC loop tracks and removes the modulation prior to carrier demodulation. This way the alarm telemetry does not interfere with the normal radio operation.
The RMAS Alarm Receiver Unit connects to the terminal radio receiver AGC control voltage and demodulates the telemetry stream. Now the RF repeater alarms can be displayed and extended to other supervisory equipment.
Normally this alarm telemetry is transmitted in one direction to one alarm receiver. For greater system redundancy in duplex repeaters, carriers in both directions can be modulated, transmitting in both directions to alarm receivers at each terminal end.
Further, the RMAS-120 has provisions for serial output at the transmitter for local supervision or to connect through an auxiliary radio link such as UHF radio.
Versions of the RMAS-120 now include 900 MHz UHF radio link equipment built-in. The telemetry radio links can typically operate up to 60 miles LOS from the repeater site.
A.15 The RF Repeaters need their own station license for FCC controlled frequencies ( adding a repeater in an existing path would require a station license for the repeater. ).
 
 
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