Welcome to
Azur Electronics

The 438A is a sophisticated microprocessor controlled dual channel power meter which can measure ratio and difference of power levels from 2 different sources. It measures absolute power in Watts or dBm, and relative power in dB. Depending on the power sensor used it can measure power from 100pW -70dBm to 25W +44dBm at frequencies from 100kHz to 26.5GHz. It originally cost $4,900 in 1986. A HP Manual was downloaded from the Web.

Front view
Rear view
Top view with cover removed
Bottom view with cover removed

Frequency Range: 100kHz to 26.5GHz (10MHz min with 8481A/8484A Power Sensors).
Power Range: -70dBm 100pW to +44dBm 25W depending on Power Sensor used.
Power Reference: 50MHz at 1mW into 50Ω.


Front Panel:
Power Sensor Inputs 2 Special Connector
Power Reference Output N-type Female
Rear Panel:
Recorder Output BNC Female

November 2006

Cleaned-up and powered-up ok. Initial display lights all segments.

Initial power up display
Display with no sensors connected
I use this as my 'reference' power meter. Extra facilities are: a programmable digital filter for optimising resolution and measurement speed; independent offset in dB values for each channel, 0.001dB resolution available; and a power difference mode for displaying absorbed power in transmission lines. Up to 19 different operating states of the meter can be stored into non-volatile memory for later recall. The power reference output and calibration controls are used to calibrate the particular power sensor in use.

Top PCB hinges up
Battery BT1
November 2016

Checking all the specialist batteries in my test equipment, see Batteries In Test Equipment. The 438A has a 3V 0.16AHr Lithium Battery on A3 Microprocessor Board Assembly, Reference A3 BT1, Part No 1420-0314. Made by Matsushita Electric BR2325 3V.

The battery maintains the supply voltage to the RAM. The 438A needs powering up occasionally to recharge the battery. 

January 2017

A Quick Calibration Procedure:

1.   Power On.
2.   Power Ref 50MHz Oscillator off, check Oscillator light is off.
2.   Connect 11730A Cable and Sensor to Power Ref output, 8481A direct,
      8484A requires 11708A 30dB Attenuator.
3.   Press Zero key and wait for routine.
4.   Press Cal Adjust and enter reference calibration factor printed on Sensor
     label, eg. 8481A at 2GHz is 98.5%, press 98.5 Enter and wait for routine.
5.   Power Ref on, check Oscillator light is on, press Cal Factor and enter same
     reference calibration factor, 98.5 Enter.
6.   Display should now read 1mW or 0dBm for 8481A and 1µW or -30dBm for
7.   Switch off Power Ref, check Oscillator light is off.
8.   Disconnect Sensor from Power Ref output.