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The 8443A can be used with the 8553B RF Section to make swept insertion loss and return loss measurements over the 100kHz to 110MHz frequency range.  In the 'Track Analyser' mode, it provides a CW signal which tracks the tuning frequency of the 8553B and in the 'Restore' mode it provides an enhanced replica of the signal indicated by the marker on Spectrum Analyser's display.  A oven controlled frequency counter and precision attenuator are included.  The 8443A cost $4,600 in 1980.  The Manual has been downloaded.
Front view
The Front Panel has a RF Output 100kHz - 110MHz 50Ω BNC on the right
and an External Counter Input 50Ω BNC on the left.
Rear view
The Rear Panel has an External Timebase Input 1MHz 1V 50Ω BNC at the top and a Timebase Output 1MHz 1V 50Ω BNC at the bottom.  The special D-type connector provides inter-connections to the 141T Spectrum Analyser.  The 50 way Amphenol socket provides the digital output which is a BCD output of the counter reading.  The Unblanked/Blanked switch selects if the leading zeros of the counter display are blanked or not.
Top and bottom views with the covers removed
The special cable (08443-60009) required to inter-connect the 8443A to the 8553B via the 141T. For details see
HP 141T External Connections.
Spectrum Analyser (with 8553B RF Section) display showing the Tracking Generator output tailing off above 110MHz with the counter indication of 110MHz approx.  The counter uses nixie tubes for the display (circa 1978), apparently later units use a LED display.
February 2009
Despite being shipped from the USA, the 8443A only needed a good clean up and worked first time.  The 'Standby' lamp is blown so a 28Vdc 24mA T1 bulb and spare is required.  The bulbs in my scrap unit were also blown, so maybe it would be better to replace these with LEDs.  Operators checks carried out and all ok.  Most of the Performance tests done.