Paul Burridge wrote:

Hello guys,

I recently picked up an old vector network analyser in working order
but minus the 3 interconnects between it and the
transmission/reflection bridge. These are specified in the manual to
be exactly 24" long, 50 ohms and terminated by N-type plugs.
I've been told the length of these patch leads is quite critical to
getting accurate measurements with this VNA, but am at a loss to work
out why 24" is specified when the frequency range of this device is
4Mhz to 1300Mhz. If it were only capable of measuring at one fixed
frequency, I could understand the need for a specifically cut length
of some fraction of a wavelength.
Can anyone explain the relevance of 24" in this context?
Also, will *any* 50 ohm coax suffice for this purpose or has it got to
be something special?
Thanks,
P.
If they specify a physical length (24"), and nothing else will do, then
the type of coax is absolutely critical as its velocity factor will
determine the electrical length.

However I suspect the bridge output is not at signal frequency but DC
so the cables will not be critical. It is very difficult to see how
they could make it work to 4GHz with several wavelengths of coax in
the signal path, acting as an impedance transformer. Two feet is a
significant length even at HF, and will shift the phases considerably.

vy 73

Andy, M1EBV