Antenna questions

jerry wass wrote:
RST Engineering wrote:

And you measured this in a 50 ohm system? You are in line for a
Nobel
Prize, my friend.

Jim



"ELIPPSE" wrote in message
oups.com...

Hi, George!
I finally found my notebook with my antenna VSWR results, and sad
to
say, I must apologize for an exaggeration about the antenna being
less
than 1.2 from 108 to 136; it wasn't. Here's the actual: 1.2 -
119/144;
,1.5 - 109/148; 2.0 - 108/150. Here are the dimensions: Each
antenna-half element was shaped as a triangular segment of a circle
15.125" long (radius), 13" across the tips of the segment
circumference, with the two elements separated by 3/4". The inner
ends
were 3/4" wide. Increasing the radius to about 16" would probably
center the response over the aircraft VHF band better. Paul


Does this look like one of the old timey TV "Bow Ties " of the 50's
??






Hi,
Yes; they look similar to those old UHF bow-tie antennas! Referring to
Fig 8-15 on page 355 of Kraus' "Antennas", it can be seen that the
feedpoint resistance of a 30, 60, or 90 deg. triangular antenna over a
ground-plane is 50 ohms between about 0.17 to 0.2 lambda. Using two
triangular elements each about 0.14 to 0.16 lambda yields 25 ohms each
for a 50 ohm 1/2 wave dipole. Antenna designers have always made use of
thick elements to substantially reduce the drive-point impedance,
physical length and increase the bandwidth of dipoles when practical.
Notice that the 15.125" length of each my antenna's two elements
corresponds to 0.156 lambda, not including feed-point separation. Fig
8-15 also shows that these triangular elements also have near-zero
reactance at these lengths! I'm surprised that the reference I
presented was not consulted before any comments were forthcoming! This
type of antenna is so simple to make that it is unfortunate that those
with airplanes with non-conductive structures have not made use of
their simple construction, low VSWR over a wide bandwidth, and
decreased physical size in making concealed antennas in the past.
Those 1/4" or 1/2" wide copper-tape antennas so many use, with their
constictive resonant bandwidth, high off-resonance VSWR, and long
length would do well to replace them, if possible. If not, one thing
they could do would be to modify them by adding a number of additional
shorter tapes splayed out from the feed-point in a triangular pattern
to approximate the full triangle shape. Perhaps someone could do some
experimentation of this multiple-tape type of antenna and report back
on this forum with the results, so that others could modify their
already-installed antennas this way. Paul