Comment by james_a_craig

Thanks, it's really useful to have a reference point. Having played about a bit with which device is left to warm up, I'm fairly sure it's the 85102 (IF box) that's drifting. I've also tried my old 8350B sweeper instead of the 8341B and although the pattern's very different (different band-switch points) it drifts about equally badly. The odd bit is that it looks like it's related to the sweep position - I get a sawtooth effect as it drifts, like so: https://www.jamiecraig.com/wp-content/uploads/2024/06/image....