wrote in message
oups.com...

Steve Nosko wrote:
Another consideration is the fact that these are not full half wave
*radiators*, but shortened approx to 66%, or 0.33 lambda (when using
this
coax). I

Then that's a big problem.

Unless the outside of the cable has the same Vf as the inside, the
sections won't have the correct phasing.

If I sounded like I was saying it was a "good" antenna I'll clarify.

As I haven't actually measured any, I may be talking out of you-know-where,
but will anyway...

To pick at a point.
I believe the phasing comes out correct. That is, you should be able to
get 180 degrees change in the coax sections. However, because the resulting
outside radiating element is shorter than a half wave (and they are touching
end-to-end ), the element spacing is closer that you get with even full half
waves stacked end-to-end and therefore the lobe compression will be less.

Also, as the phase departs from 180, due to measurement errors, you get
further degradation and then the coax loss means unequal power in the
elements, so things go down hill fast. I would suspect that simply putting
a 1/4 antenna outside the box would give same-or-better performance --- and
save the possiblilty of cutting up your fingers with the Exacto.

In spite of the bad science, with RF being RF, it *could* work out that
just having some lesser power extricating itself from the upper quarter wave
element may provide the poor bloke with improved reception. What do they
have inside the computers or cards anyway? --- it most likely isn't a clean,
in the open, well defined antenna, but some compromise design. Good enough
is always good enough even if good enough *is* 20 dB down.
Another source of false science is the location/orientation of this
antenna and the one it is talking to. This construction (assuming he mounts
it upright the way we might think) is assuming that the WiFi antenns is
horizontally in line with his and the polarization where he is, is vertical.
You have an RF sea to swim in.

73, Steve, K9DCI



Phelps Dodge did that two ways.

First, when they used solid dielectric coax, they filled the antenna
with a very thick wax that gave the correct Vf on the outside of the
shield.

Second, when they used air insulated coax inside, they suspended the
coax in air with only an occasional piece of foam for spacing.

There is more to this antenna than just throwing some .66vF sections in
series! Every coaxial collinear I have built and measured from articles
in Ham mags has had virtually no useful gain at zero degrees angle over
a dipole.

73 Tom