I’m working on an article that addresses this problem, among others.
A way to do this is with a VNA and an observation antenna. The observation
antenna can be almost anything with the same polarization as the antenna(s) you
are testing. It does not need to be resonant. It does need to be in the "far
field,” a subject that some may debate but let’s say a couple of wavelengths
away should be enough. The temporary feedline can be something cheap, like RG6
or RG58. OR… if you have another antenna of almost any kind that happens to be
far enough away, that can be the observation antenna.
Using a VNA in transmission (S21) mode, you can see the _relative_ magnitude
and phase of the path between your antennas under test and the observation
antenna. Because it’s all relative, you don't have to worry about the
observation antenna being calibrated in any way, nor do feedline losses matter.
If the observation antenna is located farther from one antenna under test than
the other, you can correct the phase by estimating the path lengths and using
the speed of light.
-Gary NA6O
>
> I have posed this question to a number of people over the last few years -
> and I have gotten some interesting ideas but I am not sure any of them have
> provided a simple or repeatable way of making such a measurement. I have not
> tried any of they yet but I think I am getting to that point.
>
> So, I thought I would cast a larger net.
>
> On the simple side of things - if I have two antennas - lets say verticals at
> some distance from each other with coax coming from them is there some way to
> measure the phase difference? Could I get some value out so that I know how
> much delay I need to add to one to get them in phase for a given signal?
>
> Or lets say I have two yagis on a tower fed with coax and I would like to
> verify they are in phase or at least close - can I measure this in some way?
>
> What if I have say a 48 foot boom 10m yagi and a 24 ft boom 10m yagi on a
> tower at 60ft over 30ft. If there a way for me to measure the phase
> difference?
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