[R-390] Signal Generator Impedence Questions

[Barry]

Gents,

The IF alignment procedures for the R390A state to connect the URM-25* to
the input connector using an impedance matching adapter  (either Test
MX-1487/URM-25D or CU-206/URM-25F depending on which generator you have).
Assuming the URM-25* is 50-ohm output, what does this converter do?  I find
it odd that the adapter is mentioned for the IF GAIN ADJUSTMENT procedure,
but not for the IF alignment procedures even though the generator is
connected to the IF module the same way for both procedures.

I assume the input impedance of the IF module is something other than
50-ohms and the adapter is being used to match the two impedances, but I
don't know what the input impedance of the IF module is.

I have a GR1001A signal generator which, for most attenuation settings, has
an output impedance of 10 ohms.  The reason I'm asking about the above
adapters is I'd like to construct a proper matching network for my 10-ohm
generator to work the same way as the 50-ohm generators do for the IF
alignment procedures.

Another question:  The instructions state to set the output at 150uV for the
IF GAIN ADJUSTMENT procedure.  If I'm using a different adapter for 10-ohms
versus 50-ohms, will I need to change the output setting to something other
than 150uV to account for the different adapter impedances?

Thanks!

Barry - N4BUQ