At 08:29 PM 12/27/2006, Telegrapher9@aol.com wrote:
>Has anyone here had good results from any of the non-MFJ impedance meters? I
>have an MFJ-259 and 269 and they are handy to have but not very
>accurate in my
>experience. I have made lab measurements against these and the results are
>not as good as I'd like.
How good would you like?
Most "ham" oriented instruments are going to be in the "few percent" range.
>At work I designed a network analyzer for production S21 measurements and it
>beats an Agilent 4395A VNA for accuracy. I'm tempted to adapt it for S11
>measurements but I'm a bit lazy. Some other time.
>
>Ten Tec has a unit that looks nice, I think it uses the Analog Devices AD8302
>gain/phase detector. This isn't the best thing in the world but it would be
>good enough for my uses. But with a price of $600 I'd like to find
>something a
>bit more reasonable.
The big questions are going to be things like how much automation do
you need, dynamic range, and selectivity. Do you want to do a cal
with standards?
Do you want a self contained widget that has it's own readout? or is
some suitable peripherals for a PC and a stack of software ok?
There are versions of the "three meter" bridge out there.
People have adapted an Analog Devices DDS eval board for the source,
and then used an RS232 readable DVM and some diodes. (or, yet another
eval board with something like a 8 input 16 bit A/D)
If you have a oscilloscope with a computer interface, you can
probably make the measurements with it and some sort of bridge, and a
bit of software to post process.
There's also the "6-port network" type of measurement, although
getting it to work over multiple octaves is a bit tricky.
Jim, W6RMK
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