gerling GA3008 Operational manual

GERLING
Gerling Applied Engineering, Inc.
P.O. Box 580816 ♦Modesto, CA 95358
www.5800mhz.com
Product User Manual
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Model GA3008
Dual Microwave Power Monitor, 5.8 GHz
Document # 930042, Rev. 1

Product User Manual Page 2
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
REVISION HISTORY
REV. DESCRIPTION DATE APPROVAL
1 PROTOTYPE RELEASE 15JAN04 JFG
WARRANTY
Products manufactured and sold by Gerling Applied Engineering, Inc. (“GAE”) are
warranted to be free of defects in materials and workmanship under normal use and
service for a period of twelve (12) months from the date of original shipment. GAE’s
obligation under this warranty is limited to repairing or replacing, at GAE’s option, all
non-consumable component parts. Consumable parts are specifically excluded from
this warranty and may include, but are not be limited to, magnetrons, fuses, lamps,
seals, o-rings, v-belts, and fluids. All warranty repairs are to be done at GAE’s facility or
as otherwise authorized by GAE. All shipping charges for warranty repair or
replacement are the purchaser’s responsibility unless otherwise agreed to by GAE.
This warranty supercedes all other warranties, expressed or implied. No warranty is
given covering the product for any particular purpose other than as covered by the
applicable product specifications. GAE assumes no liability in any event for incidental or
consequential damages, financial losses, penalties or other losses incurred in
conjunction with the use of GAE products.
DOCUMENT CONVENTIONS
NOTE: Means the reader should take note. Notes contain
helpful information, suggestions, or references to other sections,
chapters, or documents.
CAUTION: Means the reader should be careful. You are doing
something that might result in equipment damage or loss of data.
WARNING: Means danger. A situation exists that could cause
bodily injury or death. All personnel must be aware of the hazards
involved with high voltage electrical circuitry and high power
microwave devices.

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Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
WARNING
All microwave power monitors manufactured by GAE, Inc. are intended for use with
other equipment capable of producing a microwave field that is potentially hazardous to
operating personnel. They must never be connected or operated in a manner that
allows a field in excess of 10 milliwatts per square centimeter to be generated in an
area accessible to operating personnel. Contact GAE, Inc. for technical support prior to
installation and/or operation of these units if there is any question or concern about
microwave leakage.
All waveguide flange and electrical cable connections throughout the system must be
secure prior to operation. Never operate the microwave generator without a properly
rated absorbing load attached. To ensure safe operation and prevent microwave
leakage, the equipment must be periodically inspected and maintained as required or
recommended.

Product User Manual Page 4
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
TABLE OF CONTENTS
EQUIPMENT DESCRIPTION ......................................................................................... 5
General Specifications 5
INSTALLATION .............................................................................................................. 6
Preliminary Inspection 6
Waveguide Configuration 6
Flange Connections 7
Crystal Detector Installation 7
Meter Connections 7
OPERATION................................................................................................................... 9
Basic Operation 9
Coupling Factor and Directivity 9
Performance Considerations 9
MAINTENANCE AND CALIBRATION ......................................................................... 11
User Calibration 11
Zero Adjustment 11
Scale Calibration 11

Product User Manual Page 5
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
EQUIPMENT DESCRIPTION
The model GA3008 Dual Microwave Power Monitor is designed for
use in high power microwave networks to measure the level of
microwave power flowing in the waveguide. These devices are
typically used for monitoring power delivered to and reflected from
process loads.
The attenuated microwave output signal from the coupler probe is
rectified by a crystal detector diode to produce a voltage signal.
This signal is delivered to an analog current meter that is calibrated
with the specific detector and coupler as a set. Detector diodes
characteristically have a high temperature coefficient that causes its
transfer function to drift with variation in ambient temperature.
Consequently, the user should note that all power monitors using
detector diodes are subject to a certain amount of error due to
changes in ambient conditions.
Another common characteristic of analog waveguide power
monitors is that their calibration is waveform dependent. For
example, monitors calibrated for use with a pulsed output
microwave generator will give an inaccurate reading when used
with low ripple generators. Consequently, all GA300x series
monitors are identified with the waveform used for calibration.
General Specifications
Waveguide WR159
Flange CPR159F (UG1731/U)
Frequency 5.8 GHz +/- 75 MHz
Power (continuous) 1 kW maximum
Meter Scale (both) 1 kW
Accuracy +/- 5% of full scale @ 25°C
Coupler Directivity 23 dB minimum
Cables RG-58/U, BNC male connectors, 6’ long

Product User Manual Page 6
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
INSTALLATION
Preliminary Inspection
Upon arrival at the installation site the GA3008 power monitor
should be thoroughly inspected for damage or wear caused during
shipping. Any visible damage to the packaging material or the
power monitor components should be noted and reported
immediately to the shipping company in accordance with standard
claims procedures. The following components are included:
a) GA3115 dual directional coupler
b) Crystal detector (2x)
c) Meter set
d) BNC cable, 6’ long (2x)
e) GA3008 Product User Manual (this document)
Waveguide Configuration
The waveguide coupler can be connected to and used with any
common waveguide component having a compatible flange (see
below). The mounting position can be in any orientation.
A common configuration is to detect the power flowing to and from
the process load. When using a directional coupler, it is important
to note that the coupler should not be located between the tuner
and the process load. Note the direction of the “FORWARD
POWER” arrow and be sure it is oriented in the desired direction for
monitoring power. Figure 1 below illustrates a typical waveguide
configuration for forward and reverse power monitoring using a
directional coupler.
Figure 1. Typical waveguide configuration with directional coupler
for forward and reverse power monitoring.

Product User Manual Page 7
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
Flange Connections
Both flanges of the waveguide coupler must be properly connected
to another waveguide component. Bolts and nuts must be installed
at all flange bolt holes on both flanges prior to operation.
Microwave Leakage – Regulatory limits for microwave leakage
relate to standards for human safety and interference with other
electronic devices. Standards for human safety as adopted by
OSHA, the International Electrotechnical Commission (IEC) and
other regulatory agencies limit leakage to 5 mW/cm2measured at 5
cm from the leakage source under normal operating conditions, and
10 mW/cm2at 5 cm from the source under abnormal operating
conditions. The U.S. Federal Communications Commission (FCC)
has established regulations limiting the emission of energy at
frequencies outside the ISM bands. All GAE waveguide
components meets these requirements when properly connected to
another waveguide component.
Crystal Detector Installation
The crystal detectors mount on the probes of the waveguide
coupler by screwing onto the Type N output connectors. Care must
be taken to avoid cross-threading the connector or applying excess
torque. A finger-tight connection is both adequate and necessary.
NOTE: Crystal detectors are identified by an “F” or “R” in the serial
number. These refer to Forward and Reverse power and designate
the respective probe onto which the detectors are to be mounted.
Installation onto the wrong probe can yield inaccurate readings.
Meter Connections
Two BNC jacks are located on the back of the meter set. Connect
one end of each BNC cable to these jacks and the other end to the
BNC (output) jack on the respective crystal detectors corresponding
to Forward or Reverse power. See Figure 2 below for typical
connections.

Product User Manual Page 8
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
Figure 2. Meter connections to dual directional couplers.

Product User Manual Page 9
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
OPERATION
Basic Operation
Once installed, the GA3008 dual power monitor will operate without
any need for operator involvement. No adjustments or settings are
available or necessary.
Each meter has a calibration label indicating the actual power
levels for given meter readings. Although the meter scales were
designed based on the average values for a large lot of detectors,
the differences between actual values and meter readings may vary
due to variations in crystal detector transfer functions.
CAUTION: Care must be taken to avoid operating the
microwave generator at power levels exceeding the rating of the
power monitor. Excessive power levels can cause damage to the
crystal detector(s) and/or meter set.
Coupling Factor and Directivity
Directional couplers, by definition, are designed to sample the
power propagating in one direction only. The most important
parameters relating to their performance are coupling factor and
directivity.
The coupling factor is the attenuation between waveguide power
and the output signal as defined by the following equation:
Waveguide power
Coupling Factor = 10 log
Probe output power
Directivity is the attenuation between output signals derived from
sampling the same waveguide power in opposite directions as
defined by the following equation:
Probe output sensing in normal direction
Directivity = 10 log
Probe output sensing in reverse direction
Performance Considerations
Since all directional couplers lack perfect (infinite) directivity, power
measurement errors result when power is propagating in both
directions. An example of the potential measurement error is shown
in Figure 3 for a case in which forward and reverse power are 1500
Watts and 50 Watts, respectively. In this case the maximum
possible measurement error for a coupler having 25 dB directivity is
approximately +/- 30 Watts, or 2% of the reading. The error will be
greater for higher reverse power levels. Note that this chart is only

Product User Manual Page 10
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
for a specific case of forward and reverse power and that the
curves are different for other power levels.
1350
1400
1450
1500
1550
1600
1650
15 20 25 30 35 40 45
COUPLER DIRECTIVITY [dB]
FORWARD POWER [Watts]
0
10
20
30
40
50
60
REVERSE POWER [Watts]
Indicated
Forward
Power
Maximum
True
Forward
Power
Minimum
True
Forward
Power
True
Reverse
Power
Figure 3. Error limits of true forward power for given indicated
forward power and true reverse power.
The above chart is made available to the user by GAE in the form
of an MS Excel spreadsheet. Specific values for indicated forward
and true reverse power levels can be entered to see the resulting
error limits for that case. Contact GAE to obtain a free copy of this
spreadsheet.

Product User Manual Page 11
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
MAINTENANCE AND CALIBRATION
The GA3008 dual power monitor is designed to be maintenance
free and does not require any user maintenance under normal
operating conditions. However, calibration of the power monitor
may be necessary after a period of time as the meter and crystal
detector performance can drift. A calibration period of one year is
recommended.
Although the GA3115 dual directional coupler is a very rugged and
stable device, even the slightest movement of the probes inside its
mounts can change coupling factor and/or directivity. In the event of
probe movement, or damage due to excessive power levels or
mishandling, the coupler should be repaired and/or recalibrated by
GAE. Contact GAE for information on repair and calibration
services.
User Calibration
While the waveguide coupler and meter set both require
adjustments for calibration, GAE recommends that only the meter
set be adjusted by the user. Proper adjustment of the coupler is a
tedious procedure involving simultaneous measurement of coupling
factor and optimization of directivity. As this procedure is typically
beyond the capability and resources of most users, we recommend
that couplers be returned to GAE for calibration.
Each meter in the meter set has two adjustment points, one to zero
the meter and one to calibrate the scale.
Zero Adjustment
Disconnect the BNC cable at the back of the meter set and adjust
the screw on the front of the meter using a small screw driver until
the meter pointer is at zero.
Scale Calibration
This procedure requires a separate power measurement device
that can be used as a calibration standard. GAE recommends using
a previously calibrated digital power meter such as the Hewlett-
Packard model 437B power meter with the model 8481A power
sensor. The following procedure assumes the use of this meter.
1. Install the coupler in the waveguide setup between the
microwave generator and a load having high return loss (such
as the GAE model GA1221 Dummy Load).
2. Connect the HP meter and sensor to the coupler probe
corresponding to the meter to be calibrated. Set the OFFSET

Product User Manual Page 12
Model GA3008 Dual Microwave Power Monitor, 5.8 GHz
 2004 Gerling Applied Engineering, Inc. Modesto, CA
value to match the coupling factor of the coupler probe as
indicated on the coupler body.
3. Operate the microwave generator at a power level near the top
end of the meter scale.
4. With the microwave power still on, disconnect the HP power
sensor and connect the crystal detector and meter to the same
coupler probe.
5. Remove the meter housing cover and adjust the potentiometer
inside the meter housing until the meter reads the same as
measured in step 3 above.
6. Disconnect the crystal detector and reconnect the HP sensor to
verify that the measured microwave power level is the same.
Repeat steps 3 thru 6 until both meters read the same.
7. Operate the microwave generator at the lowest power reading
on the Meter Scale Calibration label (located on the top of the
meter housing cover) as read by the analog power meter.
8. Disconnect the crystal detector and reconnect the HP sensor.
Record the reading in the “Actual” column next to the
corresponding meter reading.
9. Repeat steps 7 and 8 for all values in the Meter Scale
Calibration label.