[Test-Equipment] Applied Communications SDU 2185 HELP

[Scott Schappert]

G'day Testers and their tools !

I have two Applied Communications (Apcom (Applied Communication) or Astrocom
(Astro Communications Lab) I presume ?) SDU 2185 question:

I have observed on two different SDU's of the same flavour, interesting
behavior.  The SDU's seem to work fine, except they exhibit a sweep.  Not
always, but normally after five minutes or so.  They are repeatable and
predictable, and outwardly appear to be thermally related.

The sweep issue is that the center frequency travels from 1.0 mm at narrow
and 80 percent at wide. Most often the center frequency starts out as what
you would consider normal; stable, 21.4 MHz.  It seems to be a vertical
synchronization event that is very consistent and the time frame of the
event is based on the adjustment of the band width view.  You pointed out
exactly my concerns in regards to this issue being known as a "feature"  But
with no documentation, I cannot assume anything.  The displays are real neat
with a serial port on them.  Have no idea what the command structure is, or
its purpose.

I have no documentation on these SDU's.  Does anyone out there know of these
units, and especially if someone might shed some light, or has documentation
or other intel relating to RS232 functionality ( serial access on these
SDU's )

I want to aggressively seek data, manuals and the most valuable of all:
wisdom, to get these SDU's running correctly.

Any help, even of a speculative nature will be openly accepted.

Kindest regards, and thanks in advance for any replies !

-Scott