More TDR porn.
This is the 11801/SD-24 with a good quality SMA-M/N-M cable. This particular channel has a 23 ps rise time on the open APC-3.5 connector so it is able to test to about 15 GHz accounting for the pulser rise time and the input rise time.
From the bottom going up:
SMA-M/N-M cable only. As can be seen the cable and the N-M connector are not a very good match above 12 GHz. No real surprise there.
Cable and Astrolab N-F/SMA-F open.
Cable, Astrolab 16301 N-F/SMA-F adapter and a Radiall SMA-M terminator.
Chinese APC-7/N-F adapter attached to the cable with the APC-7 side open. The reflection from the open APC-7 connector shows precisely the plane of contact.
A pair of the Chinese APC-7/N-F adapters back to back with the N-F open
The top trace is a pair of the Chinese APC-7/N-F adapters back to back with an Inmet 64671 Model 3070M terminator.
The opens show the reference plane for each of the connections, though with a slight delay because of the 23 ps rise time.
The capacitive discontinuity at the cable/connector interface is frequencies above 12 GHz. So the Chinese APC-7/N-F adapters I received are certainly acceptable up to 3 or 6 GHz. Which is not to say the ones @orin received are.
I ordered an HP APC-7 short and open, a couple of HP 900A APC-7 loads and an APC-7 jumper. When those arrive I'll set up my 8753B/85046A and compare the frequency domain for these devices.
These plots show that the N interface is a bigger issue than anything else.
Have Fun!
Reg
Edit: Added additional trace and rewrote the annotation.