[R-390] R-309A T503 differences

[Larry H]

Hi Tom,  I don't think the problem you described here is going to make any difference on the sensitivity measurement.
If your sensitivity is low only on bands 0 to 7, then the problem is probably in the 1st mixer or var IF.  If it's low on all bands, then it could be the 2nd mixer or 2nd var IF or the 3rd mixer or the main IF strip.  How bad is it?  Are you using the DA-121 impedance matcher between sig gen and rx bal input?  You need to and account for the loss in the pad.  It's 55% or 9.1 db.  Have you tried measuring the IF with the 150 uv in?
Roger Ruszkowski (Flowertime01) did a writeup in the y2kr3 about measuring the IF deck snr.  He says (and I   agree) that you need close to 30 db snr here to get good snr in the rx.  Take a look at it.
Regards, Larry