Peninsula Engineering Solutions RMAS-120 Troubleshooting Manual

Technical Note
Introduction
The RMAS-120 Repeater Monitor and Alarm System
provides supervision of microwave RF repeaters.
Alarm and status information is encoded into a serial
data stream that is then amplitude modulated on the
microwave carriers being amplified by the RF
repeater. In some cases, this serial data stream
(telemetry) is carried by an auxiliary UHF radio link.
The telemetry signal and RMAS-120 are designed to
be compatible with a wide range of microwave radio
terminal equipment.
With the wide range in equipment and circumstances
of the applications, there are times when the data
recovery may be difficult to setup. This trouble-
shooting guide is intended to assist in diagnosing and
resolving many common problems.
The telemetry data is sent at a very slow rate in order
to be compatible with most radio Automatic Gain
Control, AGC circuits. The data timing fits within the
frequency range of natural
dB/second or 1dB/10 msec).
Common Problems
1. Receiver does not synchronize
1.1. The most common reasons the receiver will
not synchronize are:
•
No or Weak Signal
• Interference
• Inverted Data
• Incompatible AGC
2. Basic Checks
2.1. Check RMAS-120
following:
2.1.1. DC Power is applied and main switch is ON.
2.1.2. Modulation switches are set for the intended
direction of transmission. Note: 2-switches per
modulated frequency.
2.1.3. Microwave carriers are present and setup
properly.
2.2. Check RMAS-120 Receiver for the following:
2.2.1. Receiver shelf is grounded to the equipment
rack. Use power connector ground. The chassis
ground is not enough. The chassis is isolated from
the circuit board ground. Proper grounding is very
important.
Peninsula Engineering Solutions may change specifications as necessary to meet industry requirements.
Peninsula Engineering Solutions, inc.
POB 1095
Danville, California 94526, USA
RMAS-120 Trouble Shooting Guide
fast fading (100
Transmitter for the
Part Number: 650-1020-01
2.2.2. DC Power is applied and main switch is ON.
2.2.3. AGC + and AGC – wiring is using shielded
twisted pair from the RMAS receiver to the microwave
radio AGC or RSL voltage points. The shield must be
grounded at the RMAS receiver end, minimum.
Grounding the shield to the rack is normal. Refer to
figure 3.2 in the manual.
2.3. Check the polarity of the AGC + and AGC –
inputs. Try reversing the polarity. The data is polarity
sensitive, one direction will synchronize and the other
will not.
3. Signal Measurements
3.1. Signal measurements are important to
determine if all equipment and connections are in
working order. Refer to the table of reference
waveforms.
3.2. Start at the RMAS-120 receiver unit.
Measure the waveform at the RCVR DATA test point
on the front panel. Waveform #7 should be found.
Waveform #8 shows the RX input signal and RCVR
DATA signals. A quick test can be made with a DVM
set to AC. Signal presence normally measures 2.3 ~
3.0 VAC. This quick test does not distinguish between
signal and AC Line noise.
3.2.1. To confirm the measured signal actually
comes from the RMAS transmitter, have another
person go to the RF repeater site and turn off the
RMAS-120 transmitter power switch. If the signal
goes away when the transmitter is OFF and comes
back when the transmitter is ON, then the alarm
telemetry data is really getting to the receiver.
3.2.2. If the signal is present, look at the signal on
the oscilloscope. Look for signs of interfering signals
such as AC power line hum and noise. Power line
frequencies, 50 Hz, 60 Hz, are close to the frequency
range of the telemetry data and will often cause
synchronization problems. Grounding and shielding
are the best ways to reduce AC interference.
Waveform #9 shows strong 60Hz AC interference.
3.3. RF. The next place to measure the
telemetry signal is at the RF repeater's output. The
complete test requires a spectrum analyzer that
covers the radio carrier frequencies. A quick test can
be made using an RF power meter.
3.3.1. Quick test. Connect the RF power meter to
the RF MON SMA test port on the amplifier being
modulated by the alarm telemetry signal. This is the
same point used to set the RF output level.
© 2014 Peninsula Engineering Solutions, inc.
Telephone +1 925 837-2243
Facsimile +1 925 837-2298
Internet www.peninsulaengineering.com
Revision B1
December 2014