A yagi can be made with a direct dipole feed, which is very simple.


Please explain how. All the yagis I've heard of have a very low
feedpoint impedance. How do you use 50 ohm coax without a matching
device of some kind?

One approach can be seen at:

http://www.clarc.org/Articles/uhf.htm

This method, by Kent Britain WA5VJB, uses a combination of a
half-folded driven element, and a proper selection of element spacing,
to allow the direct connection of 50-ohm coax. They don't provide the
highest gain or F/B ratio possible with a Yagi, but it sounds as if
the sacrifice in gain is modest.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
says...

On Fri, 13 Feb 2004 10:41:01 -0500, Bob Schreibmaier
wrote:
It all depends how you tune the yagi. For example,
a two-element yagi with about 0.2 wavelength spacing,
with a reflector approximately 5% longer than the
driven element will offer a very good match to
50-ohm coax (according to EZNEC). Costs only a few
tenths of a dB in forward gain to get that match.
_________________________________________________ ________

Ok, maybe so, but a two-element yagi is a waste of time in my book. If
you're going to that much trouble to build one, add a third element and
get a little more pizzaz.

Perhaps, but this, too, may be tuned for a very good
match to 50-ohm coax at only a small sacrifice in
forward gain. You are probably aware that Force 12
does exactly this. And, of course, the Mosley TA-series
tribanders that have been on the market for some 45
years have direct 50-ohm feed with a very good match.

73,
Bob
K3PH

--
+----------------------------------------------+
| Bob Schreibmaier K3PH | E-mail: |
| Kresgeville, PA 18333 | http://www.dxis.org |
+----------------------------------------------+

It depends on what one wishes to accomplish and how long one expects the
antenna to endure.
It is assumed that the antenna is designed to survive the pressure
due to the expected peak wind velocity (at the height where it is
mounted) and expected radial ice loading. [See EIA 222F or G]
For near maximum performance on a single band (or set of single
bands) with a tower that is at least one wavelength high, a yagi with at
least three elements is hard to beat - especially if one mounts
additional antennas on the same rotating mast.

For about 1 to 2 db less than what can be achieved with a (single
band) yagi, and perhaps that much more than many triband beams, - on a
tower that is at least one wavelength high at the lowest frequency - one
may cover all of the HF bands from 14 MHz up with one LPDA (log
periodic). In my opinion, on the higher HF bands, most radio amateurs
will be best served with a LPDA in view of the span of frequencies now
available and the lack of a need to tweak well designed examples of such
antennas.
73 Mac N8TT

--
J. Mc Laughlin - Michigan USA

"Dave Shrader" wrote in
snip

And, I would use a Log Periodic!! I give up about 1 dB in gain and
acquire a 13.5 MHz to 33 MHz broadband antenna, no traps, full legal
power handling capability and a VSWR 2:1 across the full range. That
means 20, 17, 15, 12 and 10 meters all in ONE Beam.

W1MCE

Bill Turner wrote:

On Sat, 14 Feb 2004 16:35:21 -0500, "J. McLaughlin"
wrote:


For about 1 to 2 db less than what can be achieved with a (single
band) yagi,

snip

Hard core DXers will commit mayhem for one dB and will kill for two.
That's why they don't use LPDA's.

Hard core DXers have their Long Johns tuned to 14.025 MHz and won't work
more than 25 KHz from that frequency!

If you read the beginning of this post it refers to 'many hams'.

If you want maximum gain on one frequency, or sub-band, then I agree
that a Long John tuned to your favorite frequency is the way to go. But,
if you want good to very good performance across the whole HF spectrum
from 13.5 to 33 MHz, or higher, in ONE antenna then the ONLY choice,
IMO, is a LPDA.

There is a solid reason why the governments of the world use LPDAs for
State Department, FAA and Defense HF communications.

If you want maximum gain on one frequency, or sub-band, then I agree
that a Long John tuned to your favorite frequency is the way to go. But,
if you want good to very good performance across the whole HF spectrum
from 13.5 to 33 MHz, or higher, in ONE antenna then the ONLY choice,
IMO, is a LPDA.

There is a solid reason why the governments of the world use LPDAs for
State Department, FAA and Defense HF communications.




Aaaah, not so fast.
Have you checked StepIR tunable antennas with monobander performance on any
frequency within that band? Plus instant pattern flip and much less cumbersome
than LP. Read comments from users. This antenna is making LPs obsolete (unless
you need spread spectrum instant coverage)

Yuri, K3BU.

Their web page is at
http://www.steppir.com/
they have range of beams and verticals that are tunable accross the range. On
beams they do not change element spacing, but there is enough range to
maintaing good pattern and gain. Many users love them, they are weather
resistant. The idea is that they use metallic tape inside of fiberglass tubing
and motion is done by stepping motors, which are very reliable.

They are tunable to particular frequencies, so they are not "broadband" like LP
arrays, but they beat LP in performance on any frequency withing the range.

73 Yuri


I find your comment very interesting. I was totally unaware that the
IR
antenna had laterally moveable elements so it can compete with
monobanders.
Can you point me to a URL that shows how the elements are moved along
the boom?
I suspect that such a design would provide spread spectrum coverage
since it would be resonant on all frequencies.

Regards
Art

Howdy,

The thing I have noticed in my travels is that most of the quad antennas I've
seen are CB antennas.

And many of them are damaged presumeably by the wind. I seem to see the wires
"blowin' in the wind".

It's hard to beat a Yagi for gain, performance, durability, weight, cost,
ability to match, etc.

73, Jack K9CUN

It's hard to beat a Yagi for gain, performance, durability, weight, cost,
ability to match, etc.

73, Jack K9CUN



Properly designed and built Quad will beat Yagi in all the above mentioned
"parameters". Little more cumbersome to raise on a tower with guy wires, but
easily doable.

Yuri, K3BU.us

Yuri, K3BU wrote:
"Properly designed and built Quad will beat Yagi in all the Above
mentioned "parameters"."

The author of "All About Cubical Quad Antennas", Bill Orr, W6SAI says:
"The power of the 3-element or 2-element Yagi, however, is not swept
aside by the Monster Quad, no matter what the size and power gain of
this impressive antenna."

Orr says measurements with an accuracy of a decibel or better are hard
to believe. His table shows about 1.7 dB advantage for a Quad with 2 or
3 elements over the Yagi, and the boom length may be about 2/3 that of
the Yagi, he says the reason for building a Quad instead of a Yagi is
likely a matter of opinion as to the value of the small edge the Quad
may have versus the extra cost and effort to get the Quad up.

Orr says he used both the Yagi and the Quad for years as did many of his
good friends. He says objective and subjective tests show the Quad has a
definite advantage in terms of signal strength over the Yagi antenna.

Best regards, Richard Harrison, KB5WZI