Frequency Meter
General
Passive frequency meters are intended for moderate
(±0.05%) accuracy applications in microwave measuring setups. Reaction cavity types are usually
best for this purpose since they permit full power
flow down the transmission line except at the precise
tuned frequency. At the tuned frequency, a slight
amount of power (1.5 dB dip) is absorbed by the
cavity which is visible on a scope or SWR meter
display.
Key Specifications
• SWR
• Insertion loss
• Accuracy
• Tuning dip
• Spurious response
Low SWR and insertion loss are important to provide
flat power transmission off-frequency. HP’s frequency
meter features broadband coupling loops that are
very flat versus frequency. Accurate calibration is
maintained by attention to thermal considerations
and metal selection in design. Long effective scales
are provided with a highly-readable spiral dial.
Constant tuning dip is necessary to yield readable
indications at all frequencies in the band. The HP
frequency meter is carefully designed and tested
for uniformity of tuning dip. Likewise, spurious
responses are undesirable since two responses
near the same input frequency cause confusion.
Although this meter covers more than 1 octave, the
design uses a loaded coaxial cavity that prevents
resonance at 3/4 λ tuned frequencies providing
low-error operation.
HP 537A
This direct-reading frequency meter measures
frequencies from 3.7 to 12.4 GHz quickly and accurately. Its long scale length and numerous calibration marks provide high resolution. This is particularly useful when measuring frequency differences or small frequency changes. Frequency is
read directly in GHz so interpolation or charts
are not required.
The instrument comprises a special transmission
section with a high-Q resonant cavity tuned by a
choke plunger. A 1-dB or greater dip in output
indicates resonance; virtually full power is transmitted off resonance. Tuning is by a precision
lead screw, spring-loaded to eliminate backlash.
Resolution is enhanced by a long, spiral scale
calibrated in small frequency increments.
Resettability is extremely good, and all frequency
calibrations are visible so that the measurement
point is directly indicated. Overall accuracy of
the frequency meter includes allowance for 0 to
100 percent relative humidity and temperature
variation from 13 to 33 °C. There are no spurious
modes or resonances.
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Specifications
HP Frequency Dial Overall Dip at Calibration Dimensions Weight
Model Range Accuracy Accuracy Resonance Increment Connector mm (in) kg (lb)
537A 3.7 to 12.4 GHz 0.100% 0.170% 1 dB 10 MHz N (f) 118 x 146 x 89 2.3
Minimum Shipping
(4.6 x 5.8 x 3.5) (5)
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