This is a HP vector network analyser. As far as I know it is the first sweeping VNA. It was intoduced in 1967 ! It has a plugin bay, something that was very populair in the 60-70’s. (and very handy too) You could get an analog meter to read Phase and return loss with high resolution but not sweeping. The reason they made this, I think, was because customers were used to vector voltmeters. But it has two bnc’s for a X/Y monitor (or scope in X/Y mode) I bought it like that. But without a sweeper you can not use it. And not every sweeper is usable. Later I found a non workuing 8601A sweeper and a dead HP-8707 with the 8412 CRT display plug in. From those instruments and after repair I had a working setup.
In an appnote they used a counter , the hp-5326B nixie counter. Because I have that counter I coupled it to the vna. But later I found out that that appnote setup probably had a modified sweeper or counter and a marker generator. The counter has marker inputs. So in my case the counter is just sitting there, looking pretty. But still handy because if I switch to manual sweep I can use it to set things like center frequency or read points on the trace .
The 8601 is a sweeping generator with two ranges. 100 kHz to 1.1 MHz and 1 MHz to 110 MHz. It also has a 200 MHz fixed output that is used by the VNA. Tou use a power splitter to connectr the 8601 to the DUT and to the reference receiver of the VNA. For S11 reflection measurements you place a directional bridge or coupler to the output of the generator. The output of that connects to the DUT. The coupled port is fed to the test receiver of the VNA. In case of S21 measurements the powersplitter feeds the input from the DUT. The output of the DUT is coupled to the rest receiver. The VNA measures the difference in phase and amplitude between the test and reference receiver.
I use a 6dB hybrid bridge. Most commercial couplers today are for on (GHz) range only.
They also made a 8414 polar CRT display unit. I do not have that one. This vna can not do all the things my VNWA can do. Here you need to use your math skills to get things like SWR, R+jx etc. It only displays Return loss or insertion loss and Phase. The dynamic range and sensitvity is good and it is still usable. For instance aligning a filter with an analiog (and much faster) VNA is more easy. And because the external coupler, sweeper with much higher input it can handle more abuse which is good for testing HF antennas (that often carry high static voltages.