[R-390] OT: Problem with HP-606A linearity

[Barry]

Interesting update.  I changed the points where I am setting zero.  Instead 
of setting them at the absolute endpoints, I used points closer to the 
points where the error was the worst.  I used 600kc instead of 530kc for the 
low end and 1700kc instead of 1800kc for the high end.  It makes the entire 
scale have a maximum error of 0.8% with each endpoint being out +0.6% 
and -0.6% respectively.  It starts out a little high, goes low briefly, then 
back to high until nearly the upper end where it crosses back to low again.

Not sure if this is the best way to do it, but it does get me closer.  I 
know the R390A's IF transformers are peaked something like this (not at the 
endpoints, but somewhere near the end).  Maybe this is good for calibration 
procedures as well(?).

(Hope this isn't too OT for this reflector...)

Barry - N4BUQ