Switch the apparently unshieldedcable from sweep out with a shielded one and we now get something like this....
https://ibb.co/T09k88c
Probably as flat as its gonna get but...
The lashup connections are as follows to scope in xy mode
1. Generator (60hz) Horiz out -> scope X input
2. Gen sweep out —> clipped to rf dmod board—> scope DC in to Y input