> >Phse would be important, unfortunately, I haven't the network type
> >equipment to to measure it. I do have some
> >things, is there a method to measure the phase using not so
> sophisticated
> >gear?
>
> Not that I know of unless you have a vector voltmeter. You can find
> them
> at hamfests, etc. They work pretty well.
>
You could consider using just a mixer. The DC output at the IF port of a
mixer, with the *same* frequency fed into the RF and LO ports, depends
(in theory) only on the the amplitude of the signal in the RF ports, and
the phase between the two signals. If the phase difference is 90 deg,
the output is maximum positve, if its -90 deg its maximum negative, and
if in phase there is no output. See any RF book to get the exact
equations - probably something like V(dc)=Vsig Cos(phase_difference),
but dont quote me on that.
Mixers, developed for this purpose, are known as phase detectors, and
are fairly inexpensive (Minicicuits sell a good range). You will find
all the equations in their catalogue, and some application notes.
I have done some tests on mixers, with *different* frequencies in the LO
and RF ports (I usually use 200 and 200.01 MHz), and find that the phase
of the output (measured on a special bit of kit known as a lock-in
amplifier, at 200.01-200=10 kHz), depends on amplitude, if the amplitude
out from the mixer is more than about 3 mV. Hence I keep the mixer
output to < 3mV. Whether the 3mV would apply if you use the same
frequency in both the LO and RF ports, I dont know, but I would suggest
keeping the signal to the RF port as low as possible. In fact, just
about any seminconductor amp seems to show an amplitude dependant phase
shift if the signals are above about 3mV out.
I have seen one professional attempt to make phase measuing kit along
the lines I am talking about, and it did not work too well. The reasons
were never fully investigated, but the 3mV level was not know at that
time. Hence I suggest this as something someone might like to
investigate, rather than a recipe I know will work first time.
G8WRB
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