Ed,
How versed are you in the freq. tuning scheme of the 8568? Are you aware that the scheme involved toggling frequency shifts between the 1st and 2nd L.O.’s every 20MHz of freq. sweep? This was done to keep mixing products out of the 21.4MHz IF path.
I have used the 8568B and 8444A opt 059 in 10Hz and 30Hz RBW’s in very narrow spans or zero span with 5 - 20 min. stability, but only after 24 hr. warmup/runtime. The HP-Agilent TG solution was a different box with both freq. and sweep lock circuitry., which the 8444A opt 059 did not have.
I wish you great success with your 8568 TG.
Don Bitters
