Power Measurement and Meters

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Power Measurement and Meters

• NLRS Aurora
• April 26, 2003
• By
• W0AUS

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Power Measurements Methods

• Thermal
• Diode
• Photometric

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Thermal Power Elements

• Thermocouple
• Bolometric
• Calorimetric

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Thermocouple

• Differ from other sensors in frequency and power
  range.
• Low S.W.R.
• Low drift
• Wide power range

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Bolometric

• Temperature sensitive restive element
• Barretters (positive temperature coefficient)
• Thermistors (negative temperature coefficient)

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Simple Power Circuit
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HP- 430
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Calometric
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Diode Sensor

• Wide power range
• Low drift
• Low noise
• Usually requires temp stabilization
• Requires compensation circuit
• Measures peak voltage

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Diode Detector Circuit

• Uses 2 matched diodes
• The diode in the op amp is a compensating element
• Schottky diodes good choice.
• Can be calibrated using D.C.

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Diode Detector References

• Calibrating Diode Detectors, QEX Aug 1990 by John
  Grebenkemper, KI6WX
• A Simple and Accurate QRP Directional Wattmeter
  by Roy Lewallen W7EL QST February 1990
• The Tandem Match An Accurate Directional
  Wattmeter by John Grebenkemper QST Jan 1987

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Photometric
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Power Meters and Usage
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AS USM-68

• WW2 Meter
• Vacuum Tube
• 2 Heads
• 1 mWatt
• 50 mWatt
• Attenuators assorted

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HP 430

• Vacuum Tube
• Max 10 mw
• Steps 5 mw
• Many heads
• BNC cable to Head

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General Microwave

• Knock-off of HP430
• Vacuum Tube
• Same circuit as HP430
• Show up at Flea Mkt

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HP Sensor Heads

• N connector head
• N conn 200 ohms
• WR 90 Head 100 ohms

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General Microwave Head

• BNC connector
• 200 Ohms

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HP 431 Meter

• Solid State
• Max 10 mWatts
• 5 mWatt steps
• Has temp comp
• -20 db min

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HP 432 Meter

• Solid State
• Auto temp comp
• Same head as 431
• Uses 6 pin plug and cable
• Need a cable with the unit

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HP 431 432 Heads

• Heads work for both 431 and 432
• Temp compensated
• 6 pin plug and cable are required
• Head on right N 200 ohms
• Head on left WR-90 100
• Head on right 478A
• 478A 10 MHz - 10GHz
• 478B 10 MHz - 18GHz
• Max input 20 mWatt

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General Microwave Meter

• Digital readout
• Some have db and microwatt switches
• 10 pin plug
• Solid State

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General Microwave Heads

• Uses the 10 pin plug
• Temp comp
• WR-28 Waveguide in
• 26-40 GHz

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General Microwave Head

• 3 watt head

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General Microwave Head

• 10 mw head
• N connector
• 10 pin conn and cable

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HP 435 Meter

• Solid State
• Auto zero
• Temp compensated
• Thermocouple head
• 1 mWatt output for calibration
• 100 mWatt high
• -25 db Full Scale Low

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HP 436 Meter

• Solid state
• Digital readout
• Reads in db or mVolts
• Has 1 mV cal output
• Uses same head as 435
• Uses 12 pin cable
• Auto zero

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HP 435 436 Head

• Thermocouple head shown
• Diode head available
• 12 pin connector
• N connector
• Good to 18 GHz

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How to check a sensor used onthe HP 431 and HP
432

• Measure pin 1 to ground
• Measure pin 2 to ground
• A good head will measure 1000 to 5000 ohms and
  the two measurements should be within 5 of each
  other
• View looking at plug on sensor head

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Care in using a Power Meter

• Use a pad to initially measure an unknown value
  of power
• Heads CANNOT TOLERATE OVERLOAD!
• One reason there are more meters than heads
  available.
• Use pads or directional couplers to adjust the
  power level to safe value for the head

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To Measure High Power

• Use a pad that reduces the level to a safe value
  for the head and within range of the meter.
• OR
• Use a directional coupler terminated with enough
  coupling db loss to have a safe level for the
  head, and within range of the meter.
• A combination of both pad and directional coupler
  can also be used.

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Happy Power Measuring