Agilent 537A Operating Note

537A Coaxial Frequency Meter

Operating Note

Manual part number: 00536-90013
Printed in USA
March 2001
Supersedes: May 2000

Documentation Warranty

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11/16/04

Safety and Regulatory Information

Review this product and related documentation to familiarize yourself with
safety markings and instructions before you operate the instrument. This
product has been designed and tested in accordance with international
standards.

WARNING The WARNING notice denotes a hazard. It calls attention to a procedure,

practice, or the like, that, if not correctly performed or adhered to, could result
in personal injury. Do not proceed beyond a WARNING notice until the
indicated conditions are fully understood and met.

CAUTION The CAUTION notice denotes a hazard. It calls attention to an operating

procedure, practic e, o r the like, which, i f not correctly performe d or a dhe red
to, could result in damage to the product or loss of important data. Do not
proceed beyond a CAUTION notice until the indicated conditions are fully
understood and met.

Instrument Markings

When you see this symbol on your instrument, you should refer to the instrument’s

!

1SM1-A This text indicates that the instrument is an Industrial Scientific and Medical Group 1

instruction manual for important information.

This symbol indicates hazardous voltages.

The laser radiation symbol is marked on products that have a laser output.

This symbol indicates that the instrument requires alternating current (ac) input.

The CE mark is a registered trademark of the European Community. If it is
accompanied by a year, it indicates the year the design was proven.

The CSA mark is a registered trademark of the Canadian Standards Association.

Class A product (CISPER 11, Clause 4).
This symbol indicates that the power line switch is ON.

This symbol indicates that the power line switch is OFF or in STANDBY position.

Agilent 537A Operating And Service Manual

Safety Earth Ground

This is a Safety Class I product (provided with a protective earthing
terminal). An uninterrup ti ble saf et y ear th gr ound must be pr o vided from the
main power source to the product input wiring terminals, power cord, or
supplied power cord set. Whenever it is likely that the protection has been
impaired, the product must be made inoperative and secured against any
unintended operation.

Befor e Applying P o wer Verify that the product is c onfigured to match the available main power

source as d escribed in the input power configuration instructions in this
manual. If this product is to be powered by autotransformer, make sure the
common terminal is connected to the neutral (grounded) side of the ac power
supply.

Agilent 537A Operating And Service Manual

Overview

Description The Agilent 537A coaxial frequency meter is used for measuring frequency

in the 0.96 to 12.4 GHz range. Accuracy is obtained from the spiral scale.
The meter contains a coaxial line coupled to a quarter-wavelength coaxial
resonant cavity loaded with capacitance at the bottom of the band. At
resonance, power is absorbed by the cavity, producing a dip in the coaxial
line power. The frequency at which this dip occurs is read d irectly from the
dial in gigahertz.

Tunin g is accomplished b y moving a pis ton. A precision l ead scre w , whic h is
spring-loaded to pre v ent backl ash, is use d to po sition t he piston in the ca v ity.
Due to the design of the cavity, its electrical length is extended at lower
frequencies, and there are no spurious modes.

Specifications The instrument specifications are provided in Table 1 on page 1.

Table 1 Specifications

Characteristic Value

Frequency range 3.7 to 12.4 GHz
Reflection coefficient off-resonance 0.33 (2.0 SWR, 9.5 dB return lost)
Calibration increments 10 MHz
Dimensions

Height

Diameter
Weight 3-1/2 lb (1.6 kg)
Dip at resonance 1 dB (minimum)
Dial accuracy

1. Width (including connector): 4-5/8in (118 mm).

2. Overall Accuracy: ±0.17% which includes allowance of ±0.02% for 0 to 100% relative humidity,

±0.0016 per ×C from 13 to 33×C and 0.03% backlash.

1

2

5-3/4 in (146 mm)
3-1/2 in (89 mm)

±0.1%

Measurement A detector and indicator are req uired to indicat e the di p in coaxi al line power

at resonance. It is r ecommended tha t 10 dB of att enuation be placed be tween
the signal source and the frequency meter. If insufficient power is available
to use a 10 dB attenuator, an attenuator offering less attenuation may be
used, to a minimum of 3 dB. The attenuator pr events a shift in the f re quen c y
of the signal source due to line impedance changes at resonance.

Agilent 537A Operating Manual 1

Overview

The detector-indicator combination can be a thermistor mount and power
meter such as the Agilent 478A and 432A, or a crystal detector and SWR
meter. If a SWR meter is used as the indicator, the signal source must be
modulated at 1000 Hz (sine or square wave modulation). For visual display,
an oscilloscope c an be used as the indicat or. When using an oscilloscope for
swept frequency displ ays , be sur e to sweep the oscilloscope at the same ra te
as the signal source. Resonance will be noted as a dip in the oscilloscope
pattern

CAUTION Do NOT run dial into stops at either end of dial

If frequency measureme nt is one part of the measurement pro cedure, be sure
to move meter off resonance before proceeding with other measurements.

Figure 1 Type-N Connector Dimensions

Connectors The input and output connect ors are type-N, f emale and are compatibl e with

connectors whose dimensions conform to MIL-C-39012.

N-female Pin Depth: 0.207 to 0.201 in (effective 0 to –0.006)

2 Agilent 537A Operating Manual

Performance Test

Performance Test

Purpose The procedures listed in Table 2 and Figure 3 on page 7 check performance

for incoming inspection, periodic evaluation, and calibration. The tests are
performed without access to the instrument interior. The performance
standards are contained in Table 1 on page 1.

Recommended Test Equipment

Table 2 Recommended Test Equipment

Test instruments required to make the performance checks are listed in

Table 2. Instruments other than those listed may be used provided their

performance equals or exceeds the critical specifications given.

Instrument Critical Specifications Suggested Agilent Model Use

Sweep Oscillator CW and swept-frequency signal in

0.96 to 12.4 GHz range
Output: at least +7 dBM

Directional Coupler Frequency: 1.7 to 12.4 GHZ,

Directivity: >26 dB

Crystal Detector Frequency: 0.96 to 12.4 GHZ,

Sensitivity: >0.4 mV/,uW

Oscilloscope Vert. Sens: <20 mV/dm, Horiz.

Sensitivity: <1 V/cm

Counter Frequency: 0.96 to 12.4 GHZ,

Sensitivity: <–7 dBm

1. P= performance tests, T= troubleshooting.

8620C Mainframe (with
appropriate RF plugins)

779D P,T

P,T

P,T

P,T

P,T

1

Maintenance For dial-stop gear replacement and/or instrument recalibration, refer to

Figure 4 on page 1 2 . For any other repair needs, contact your local Agilent

Technologies Sales and Service office for instructions and assistance.

Return Loss Specifications

Description As shown in Fi gure 2 on page 4, two detectors are connec ted togeth er wit h a

537A reflection coefficient off-resonance: 0.35 (2.0 SWR, 9.5 dB return
loss).

modulator, swept amplitude analyzer, and a dual directional coupler in a
reflectometer test setup. The reflectometer is calibrated using a short. The
537A coaxial frequency meter under test is connected and the return
measured.

Agilent 537A Operating Manual 3

Performance Test

Figure 2 Return Loss Test Setup

Table 3 Equipment

Instrument Type Suggested Agilent Model GHz or Connector type

Sweep oscillator 8620C mainframe (with

Dual directional coupler

Detectors (2 required) –
Modulator –
Swept amlitude analyzer/oscilloscope –
Coaxial short Type-N female

Low-Pass Filter(s) 700 MHz cutoff

Termination(s) APC-7

1. Two single directional couplers connected as a dual directional coupler can also be used.

–

appropriate RF plugins)

1

778D
779D

110 MHz to 2 GHz

1.7 to 12.4 GHz

Type -N male
APC-7

1.2 GHz cutoff

2.2 GHz cutoff

4.1 GHz cutoff

Type-N male

4 Agilent 537A Operating Manual

Procedure 1. Connect the equipment as shown in Figure 2.

2. Set the analyzer control to 0 dB.

3. Set CHANNEL A OFFSET CAL switch to OFF

4. Press CHANNEL A DISPLAY POSITION push button.

5. Adjust CHANNEL A screwdriver adjustment marked POSITION to

place trace on the center graticule. Increase resolution and make fine

adjustment.

6. Place short on reflectometer.

7. Press CHANNEL A push buttons marked DISPLAY R and 10 dB/DIV

8. Set the sweep oscillator to sweep the band of interest.

9. Adjust the sweep oscillator output power level to place the trace on the

second graticule below the center graticule. (Power input is –20 dBm to

the R detector.)

10. Press CHANNEL A push button marked DISPLAY A/R.

Performance Test

11. Turn CHANNEL A OFFSET CAL control to ON and adjust the

OFFSET CAL control to place the trace on the center graticule.

12. Increase the dB/DIV resolution by steps to 0.25 dB/DIV if necessary,

adjust the OFFSET CAL control to return the trace to the center

graticule.

13. Disconnect the short from the reflectometer test port.

14. Connect the 537A under test to the reflectometer test port by

disconnecting the short and inserting the properly terminated 537A

under test.

15. Use CHANNEL A OFFSET dB thumbwheel to return the trace to the

center of the screen, or as close as possible.

16. Read the return loss at the CHANNEL A OFFSET dB window and on

the oscilloscope. Return loss is the total indication of both the

CHANNEL A OFFSET dB window and the trace on the oscilloscope.

Add the trace indication to the window reading if the trace is below the

center graticule, subtract if above.

Agilent 537A Operating Manual 5

Performance Test

17. Return loss measured should be equal to or greater than the following
limits:

Table 4 Return Loss Limits

Specification 26 dB 30 dB 40 dB

Lower Limit of Reading

Coupler Directivity

20.8 dB

9.5 dB

27.8 dB

11.0 dB

24.6 dB

10.5 dB

21.9 dB

9.8 dB

18. If the above limits are not met, test the 537A using a slotted line at the
frequency in question.

6 Agilent 537A Operating Manual

Overall Accuracy

Overall Accuracy

Specification for the 537A: ±0.17% overall accuracy.

Description A sweep oscillator, 537A under test, detector, and oscilloscope are

connected in series. The sweep oscillator is set to AF to sweep the band in
question. The 537A is set to the frequency in question and the notch located
on the trace. The sweep oscillator is set to CW and adjusted to the center of
the absorption notch of the 537A. The frequency of the sweep oscillator is
measured with a counter and co mp are d wi t h the specificati ons in Table 1 on

page 1. The sweep oscillator is set to automatic sweep and the notch depth

across the b and is checked.

Figure 3 Overall Accuracy Test Setup

Table 5 Test Instruments

Instrument Type Suggested Agilent Model Frequency Range (GHz)

Sweep Oscillator 8620C mainframe (with

appropriate RF plugins)

Directional Coupler 779D
Crystal Detector 423A
Oscilloscope 1740A
Counter 5342A

86222A/B
86235A
86240C
86245A

0.5 to 2.4

1.7 to 4.3

3.6 to 8.6

5.9 to 12.4

Agilent 537A Operating Manual 7

Overall Accuracy

Procedure 1. Connect the equipment as shown in Figure 3 on page 7.

2. Set oscilloscope for a vertical sensitivity of about .02 V/cm (ac) and
horizontal sensitivity of about 1 V/cm.

3. Set sweep oscillator for ^F automat ic sweep of about 3.8 GHz + 12 MHz
for 537A.

4. Set the 537A to 3.8 GHz.

5. Locate the frequency meter notch and center it on the display by
adjusting the sweep limits on the sweep oscillator.

6. Set the sweep oscillator to CW and adjust the frequency to the center of
the notch (lowest indication on the oscilloscope).

7. Read the frequency on the counter. Frequency should be within the
specifications given in Table 1 on page 1.

8. Repeat above procedure every 200 MHz across the band.

9. Set sweep oscillator to automatic sweep and tune the 537A across
frequency range of sweep oscillator. The notch travel across the
frequency ran ge should cause at least the notch depth given in Table 1-1.

Stop Gear Replacement

Procedure

1. Upon completion of the stop gear replacement it will be necessary to
check the frequency calibration of the instrument.

2. The followin g special tool is required for t his procedure. A W a ldes No. 3
Truarc pliers with tips bent 45 degrees.

3. For the following procedures refer to Figure 4 on page 12 and Figure 1

on page 1.

Disassembly Procedure (Numbers in parentheses r efer to numbers on drawing in Fi gure 4. To replace

the stop gear, proceed as follows:

1. Remove knob (1).

2. Scribe dial position to give approximate location of dial on dial holder.
Do not use pencil as this may be inadvertently erased.

3. Unscrew dial-window retaining nut (3).

4. Remove nut and window

5. Loosen two No. 6 Allen se t-scre ws (9) holdi ng dial. These are l ocated on
the inside or dial holder (10).

6. Turn dial holder until cap (7) is approximately flush with top of dial
holder (near high frequency stop position).

7. Scribe a line from lead screw on plunger to cap for later alignment.

8 Agilent 537A Operating Manual

8. Loosen both No. 6 Allen set screws (9) holding cap in place on lead
screw. These are internal and may be found by looking through the two
inspection holes in dial holder. These are spaced approximately 90
degrees apart.

9. While holding cap in place, back out both screws sufficiently to allow
removal of cap. This should be approximately three full turns of the
Allen screw. If spring and cap jump out, replace them with big-diameter
end of spring at bottom.

CAUTION Do not turn or remove plunger.

10. Turn the 537A upside down and remove the Truarc retaining-ring
holding dial holder (3). (This requires special Truarc pliers. It may be
necessary to adapt some of your own tools to the job of removing the
retaining ring.).

11. Lift 537A off dial holder and place base assembly upright again.
Examine both sections for pieces of broken stop gear.

Overall Accuracy

12. Inspect bearing and gear rack to make sure that these hasn’t been
damaged by portions of the broken stop gear. If any of the internal
workings other than sto p gear hav e been damaged, it will be necessary to
return to the factory for a major rebuilding.

Reassembly Procedure 1. Replace dial holder , t aking ca re not to damage gears when e ngaging stop

gear with gear rack

2. Check rotation of the dial holder. There should be approximately 11-1/4
turns of the dial. If not , dise ngage and tr y ag ain with a n e w gear posit ion.

3. When the stop gear is positioned to give approximately 11-1/4 turns
from stop to stop, secure d ial holder with th e T ruarc retaini ng ring. Make
sure ring is seated properly on inside groove of dial holder.

4. Turn dial holder to stop at high-frequency end of dial.

5. Ins ert spring into dial holder.

6. Replace cap by compressing spring. Note alignment of cap and lead
screw. See steps 6 thru 9 of disassembly procedure.

7. Tighten both No. 6 Allen set-screws holding cap to lead screws.

8. Turn from stop to stop. Check for binding or other erratic behavior. It
may be necessary to make slight adjustments in cap position so that no
binding occurs during rotation.

9. Turn dial holder counterclockwise (toward lower frequency) to expose
dial retaining set screws.

Agilent 537A Operating Manual 9

Overall Accuracy

10. Place dial on dial holder and check alignment wit h scri be mark of st ep 2.

11. Tighten both No. 6 Allen set-screws to hold dial in place.

CAUTION Do not tighten excessively as knob may not slip into place over the dial/dial

holder.

12. Turn dial clockwise near the stop at the high-frequency end and place
both cursors (6) into the dial grooves to indicate approximately 12.4
GHz.

13. Carefully replace window making sure that cursors ride in the window
grooves.

14. Align window with ba se. Window keys must be in the window retention
grooves.

15. Replace window-retaining nut.

16. Turn from stop to stop. Check for binding or other erratic behavior. It
may be necessary to make slight adjustments in screw tightness or dial
position so that no binding occurs during dial rotation.

17. When assured of smooth operation, check calibration. Calibration
should be reasonably close if ca re wa s taken i n alignment of the cap le ad
screw and dial. Replace knob.

10 Agilent 537A Operating Manual

Calibration Procedure

Calibration Procedure

Test equipment recommended for testing the 537A are listed in Table 2 on

page 3. Test equipment other than that recommended may be substituted if

their performance equals or exceeds the minimum required specifications
given. Figure 2 on page 4 and Figure 3 on page 7 list procedures for
checking instrument specifications. If dial accuracy is not within listed
specifications, adjust 537A as detailed in the Calibration Alignment
Procedure, as follows.

Calibration Alignment

Procedure

If dial accuracy of the 537A is not within specifications. The following
procedure can be used for readjustment.

1. Remove knob (1).

2. Remove base (11) retaining screws. With base retaining screws
removed, pla ce the 537A in up right posit ion and mak e electr ical hookup
for OVERALL ACCURACY TEST.

3. In the original high-frequency end setting, 12.4 GHz is set almost
one-half turn (about 150 degrees) counterclockwise from the stop. The
dial (5) is held to the dial holder (10) by two set screws (9). Check
frequency accuracy at 12.4 GHz, and if not within overall accuracy
specification, loosen set screws (9) and slip dial. T he set screws ar e
loosened from inside the dial holder; the dial must be rotated about 6
turns before the access holes become visible.

4. The low-frequency end adjustment is made at 3.7 GHz by moving
capacitiv e load with two cap screws. This adjustmen t sh oul d not chan ge
the high frequency setting.

5. Check dial accuracy in vicinity of 3.7 to 4.1 and 8.2, 12.0, and 12.4
GHz. Reposition the dial, or capacitive load if a compromise is
necessary

6. If accuracy specifications cannot be met, further disassembly is not
recommended. The unit should be returned to your local Agilent
Technologies Sales and Service office.

7. Replace base and knob.

Agilent 537A Operating Manual 11

Calibration Procedure

Figure 4 537A Repair and Recalibration.

12 Agilent 537A Operating Manual

Replaceable Parts

Table 6 Replaceable P a rts

Replaceable Parts

Reference
Designator

1 Knob 5040–6950 1
2 Screw, set 8-32 x 3/16 3030–0001 2
3 Nut, dial window retainer 00532–40005 1
4 Window K532A–18 1
5 Dial 00537–20031 1
6 Cursor K532A-20 2
7 Cap R532A–16 1
8 Spring, lead screw 1460–0044 1
9 Screw, set 6-32 x 1/4 3030–0106 2
10 Holder, dial P532A–4 1
11 Base 00537–20029 1
12 Ring retaining 0510–0069 1
13 Coupling loop assembly 00537–601
14 Bearing, ball 1410–0005 1

Description Part Number Quantity

1

15 Window support 00537–206
16 Screw, fill Hd 2-56 x 1/4 0520–0012
17 Shaft stop gear P532A–5 1
18 Gear stop P532A–19 1
19 Ring, retaining 0510–0070 1
20 Cork ring 2190–0345 1

1. See Figure 4 for parts location.

Agilent 537A Operating Manual 13