Paul Burridge wrote:

Hi all,

I need a couple of accessories to enable me to make some phase
measurements with my HP network analyzer. I'd thought I could pick
these up on ebay easily enough, but note the lack of availably with
surprise and dismay.
I need to therefore contrive two precision parts:

Firstly, 50 ohm load that's essentially non-reactive up to 1.3Ghz.
Power handling only need be a few tens of miliwatts. N-type
connection.

Secondly, a 50 ohm power splitter (one feed-in; three outputs) N-type
connections, again flat up to 1.3Ghz. No switching needed, thankfully.

If I can't source these parts elsewhere, how feasible is it to make
them up and can anyone point me to any designs on the web that might
fit the bill?

I'm aware that the introduction of any stray reactances into the
devices will render all subsequent measurements invalid so I need to
get these parts right. At least 1.3Ghz capability should be achievable
for a hobbyist with care.

Thanks,
P.

You can make a pretty good 50 Ohm termination with a PCB-mounting SMA
connector. Cut off the centre pin of the PCB-end of the connector leaving
0.5mm or less protruding (careful of your eyes, the pin can go shooting off
pretty fast, it's hard metal), and then solder two 0.1% 100 Ohm 0603
resistors between the centre pin and the outer (ground) part of the
connector. The resistors should be diametrically opposite.

I made one with 1% resistors and got the following:
s11 -30dB up to 6GHx and
s11 -47dB up to 500MHz

It helps to tweak how flat you lie the resistors on the teflon at the back
of the connector, but without a working VNA you just have to accept what
you get.

If you want a termination with a N connector, then you could use a really
good adapter with the SMA termination I mentioned above, or work out
something similar with a N connector however I have never tried that since
I mostly use SMA anyway.

I think a very accurate / flat power divider would be fairly hard to make
well unless you can get boards made with microwave substrates. If you can
work out your measurement setup such that the flatness etc of the divider
is not so important, then that would help.

There's a guy in the UK selling a one input two output type power divider
with N connectors and a 50 Ohm N termination on e-bay at the moment if that
helps you.

Chris