Jeff Liebermann wrote:
On Mon, 09 Nov 2009 10:11:42 +1000, atec7 7 "atec
wrote:

One wavelength at 2.4Ghz is 12.5cm. Guessing from the photo, there's
a total of about 15mm of exposed conductor. That's about 1/8th
wavelenth, which will still radiate rather badly, but not as badly as
I previously erroniously assumed.

Assuming the radiator is actually resonant then the vswr doesn't really
matter

Wrongo. VSWR does matter.
Depends on the feed method long as the maximum transfer of enegy takes
place
I remember as a youngster open feeder balanced into the back of the
old tube tx , still use open feeder today with good success
VSWR is a measure of impedance matching.


take a breath son getting excited can be bad for the heart on old blokes
like us

Failure to match impedances means that your antenna is no longer
working at the optimum power transfer point (i.e. maximum efficiency).
It will still work with a high VSWR, but not as well. High VSWR also
has highly undesirable side effects such as, mangled gain pattern,
radiation from undesired conductors, loss of gain, and loss of
efficiency. Resonance is a good thing, but not absolutely necessary
for proper operation. Resonance would be where the reactive
components are zero.
yes BUT it may not offer a good match no ?

Since I don't see any adjustment(s) to tune out
(resonate) the inductances introduced by the relatively long exposed
coax leads, I don't think this antenna is particularly close to
resonance.
The radiator may dip fine but the energy transffered will be radiated
badly into the ether I suspect

but as you point out the exposed centre conductor will radiate
badly and certainly not a design to be emulated by effectively stopping
the reflected rather than matching correctly .

Yep. It's like fixing the symptoms rather than fixing the source of
the problem.
Agreed , the manner of feeding also happens to radiate which of course
is bad as I did some testing a while back on some commerial yagi's and
with a fiddle the actual vswr hardly changed but energy transfer was
markidly improved