Richard Clark wrote:
On 28 Mar 2005 11:52:23 -0800, "Brian Kelly" wrote:

So two questions in this regard: Is there a way to measure the Vf of
a
wire without having to resort to using 2" Heliax to feed a dipole
and
without a lab full of HP and GR test equipment? Second, assuming
the
Vf becomes known how does one handle it during the modeling process?
Model the antenna wire lengths at an upward-shifted frequency based
on
the Vf?

Hi Brian,

1. Drive the design with power instead of low level excitation;

Sweep the dipole with a transmitter and an SWR bridge?

2. Remove half the transmission line muffling of results by using a
field strength meter to find resonance (another reason for power);

Same as above but with a field strength indicator? Just might work if I
use a 4-digit DVM and a diode.

3. Find the Vf (as you put it) by derivation against a wire model
(through the difference in lengths of bare wire model resonance to
real wire resonance);

That would seem to work but I'd expect to still have the flat curves
because of the coax losses. I'm starting to think I should go to a
lower frequency band like 40 or 80M to reduce the problems with the
coax. And to reduce the errors in cutting-to-length.

4. Use the new EZNEC which allows you to employ insulation over wire
and adjusting the thickness to conform with results found
experimentally with real wire at actual length;

.. . . all I gotta do is DO that! "The loop has been closed."

5. Assign these insulation properties to all future designs in the
modeler.

I've been using Nec Win Plus which is OK but it doesn't have the the
ability to handle velocity factors like EZNEC 4.0 can.

I don't have a big problem with scaling antenna dimensions to adjust
for the Vf because I physically model antennas with CAD first to get
the locations of the wire end points in 3D space. Which I can quickly
and easily load into NWP. The CAD program does all the tedious trig for
me. When I have a bare-wire model which "works" in NWP I can rescale
the physical model by 0.98 or 0.95 or whatever the Vf might be to get a
"close enough" fully dimensioned antenna design. But I still need to
find the Vf experimentally and we're back to square one. You fed me
some thinking fodder, I'll try a few things per above and get there one
way or another.

Tnx.

73's
Richard Clark, KB7QHC

w3rv