3flp wrote:

Hi Chris,

I am planning to make it a VNA in a later stage. For now, I just need
something to check antennas, filters, etc. So a scalar analyzer with a
good return loss bridge will do OK.

After some thought & googling around, I'll just use the original
suggestion for now. Two identical VCOs + PLLs. So in effect, I am
optimising the design for speed & easiness :-). Not for cost or
performance...

I am aware that the mixer will produce various combinations of LO & IF
frequencies. I am hoping to optimise the power levels to get the 2nd
and 3rd harmonic down to -50dBc. That should be enough for return loss
measurement. For filter response measurements, this is probably not
good enough, so I am thinking about adding a switchable bank of low
pass filters at the output. But this is slightly messy, so I'll do it
later, and only if I convince myself that it's needed.

73
Fil
VK3FLP

Hi Fil,
I think that if you use a mixer or sampler as a detector then it may well be
possible to make the receiver relatively insensitive to harmonics in the
source signal but if you use untuned detectors then it would be more of a
pain.

If you were able to do proper VNA type calibrations then you would not need
such a good return loss bridge, cables, connectors etc. I wonder whether
in this age of cheap computing power, the VNA might actually be easier to
build, for a given level of directivity after calibration.

Good luck and let us know how you get on.
Chris