Chris Jones wrote in
:

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

A two-output splitter,IIRC,uses 3 25 ohm resistors in a Y config.
Use a double-sided PCB for the ground plane between the three N connectors.

--
Jim Yanik
jyanik
at
kua.net