Kris - Quads are great antennas, but I have to disagree with you on a point
you made in your post of Mar 5;
"1) Quads have lower angles of radiation than do yagis at the same
height."
This mystique of quads coming into their own and perfroming better than
Yagis at low heights has been proven wrong by both measurement and
modeling. The Quad is not discernably better or worse than the Yagi at the
same height, low or high.
Wayne Overbeck, N6NB(?) did a nice piece on Quads versus Yagis for Ham
Radio Magazine years ago, May 1979 ?, in which he made field strength
measurements at varying angles of radiation of both a Quad and a Yagi at 6
M at varying heights. He did not measure any discernable difference in the
angles of radiation. The tests were a very nice controlled scientific
experiment. The article is recommended reading for anyone that can find it.
There is also modeling that confirms these measurements, the latest being
in the ARRL Antenna Compendium Vol 4 or 5 I think. I don't have the
reference here at hand. I would be surprised if L. B. has not looked into
this. L. B. ?
This conclusion is not surprising. The angle of radiation of an antenna is
determined by its radiation pattern in free space (absence of ground) and
the reflection properties of the ground the antenna is installed over. The
free space radiation pattern of the quad and Yagi both peak at the same
vertical angle (0 degrees) and the ground is the same for both antennas
(and hence the reflection properties) so the angle of radiation is
essentially the same.
The good reputation of the performance of a quad over a yagi is testimony
as to the difficulty of getting the extra 1 or 2 dB from a 3 element yagi
over a two element beam. The lower radiation resistance of the 3 element
beam at the higher gains translates into higher losses. In fact, in
Overbeck's study the 3 element tribanders were not significantly better
than the two element tribander he used as a reference.
Unfortunately Quads are difficult to keep up in most climates. For fixed
beams they generally do not have this problem and are a good alternate to
the Yagi.
Keep on posting. - Duffey KK6MC/5
James R Duffey KK6MC/5 DM65
30 Casa Loma Road
Cedar Crest, NM 87008
[
QRP-L Archive |
]
[
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
2000
]