I wanted to EXACTLY measure the frequency
of verticals. What I did was to build a
very simple noise bridge with only an
adjustable resistor, but without the adjustable
capacitor (and its fixed mate on the other
side of the bridge). Then what I did was
to null with a combination of varying the pot and
varying the frequency until I got 60 dB or
so of nulling. I used a signal generator
with sine wave output instead of a noise
generator, because of the need for the
extra dynamic range. This has an accuracy
in the 10 kHz class that you wanted.
For a wire dipole, you will have to
make a balanced version of this (can't
just put a balun in front of an unbalanced
bridge). I once built a balanced impedance
bridge for measuring 450 ohm open wire line.
If you just want to measure velocity, it
would be a lot simple to do it with a wire
vertical, even if the final application is
Rick Karlquist N6RK
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org]On Behalf Of
> Sent: Monday, July 08, 2002 5:53 AM
> To: email@example.com
> Subject: [Towertalk] EXACT resonant freq of a dipole --> AEA CIA HF
> Hello everybody,
> I want to EXACTLY measure the resonant frequency of a wire dipole.
> That means I cannot use a simple SWR bridge, because
> normally the resonance
> curve is so broad that I can only determine the resonant
> frequency with an
> accuracy of +/- 100kHz, based on cross-needle readings.
> I would like to determine the resonant frequency with an
> accuracy of +/-
> 10kHz, or at least with a much better accuracy than with
> the SWR bridge.
> Before I buy one, can you please advise whether I will be
> able to do this
> with an AEA CIA HF analyzer?
> It sure looks good on the manufacturers specifications. I
> had an Autek RF-1
> analyst before and I was quite dissapointed with its accuracy.
> What else do you use for tasks like this?
> Should I get the CIA or the VIA model?
> (Why do I want to measure so exactly? I want to determine
> the velocity
> factor of the wire used. The velocity factor is introduced by the
> insulation covering the wire.
> Therefore the wire elements are always a bit too long when
> cutting them to
> the dimensions taken from a computer simulation.
> This is not a problem with dipoles but with wire yagis and
> quads, where the
> parasitic elements must have exactly the proper resonant frequency.)
> Your comments are very much appreciated
> 73s Con DF4SA
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