I'm building a yagi from the measurement tables the ARRL Antenna Book. I
have the driven element finished and getting a good SWRs with a home-made
gamma match.

I'm going to mount it on a wood 2 X 2 with as many directors as will fit on
an 8 feet boom.

Any advice? (I've already read that a gamma match is a poor choice but it
did work, so we can skip that one. :-)

"Sal"
(KD6VKW)

If you delve deeper, you will read that each time you add directors - you have to recalculate the spacing between each director.
The length of each director and the spacing is very important.
Wood is a poor choice for anything more then a experiment - it is heavy, and not very strong.

If you are serious about building that antenna, you would want to look for a old UHF / VHF television antenna such as the Radio Shack VU 190.
Rob the elements off the antenna, cut them to length and mount your gamma match to it with a appropriate sized reflector.

There was a channel master VHF antenna that was made back in the 1970's that was about 24 feet long which also made a excellent donor antenna / platform for a home brew beam antenna.

Channel Jumper wrote:
If you are serious about building that antenna, you would want to look
for a old UHF / VHF television antenna such as the Radio Shack VU 190.
Rob the elements off the antenna, cut them to length and mount your
gamma match to it with a appropriate sized reflector.

There was a channel master VHF antenna that was made back in the 1970's
that was about 24 feet long which also made a excellent donor antenna /
platform for a home brew beam antenna.

In those days, we could buy raw stock from the bureau of the amateur
radio association, who obtained it from local antenna manufacturers that
we still had back then.

Dipoles already to size for VHF/UHF bands, and elements to the maximal
length required for each band, that you cut down to the correct length
for your design.

Those elements already had the mounting block and bolt just like the
commercial TV antennas. I made 2M and 70cm crossed yagis for satellite
operation out of those parts.

"Sal" salmonella@food poisoning.org wrote in message
...
I'm building a yagi from the measurement tables the ARRL Antenna Book. I
have the driven element finished and getting a good SWRs with a home-made
gamma match.

I'm going to mount it on a wood 2 X 2 with as many directors as will fit
on an 8 feet boom.

Any advice? (I've already read that a gamma match is a poor choice but it
did work, so we can skip that one. :-)


While not what you want to hear, scrap that idea. Look at the Quagi antenna
and a 10 foot piece of the grey plastic electrical conduit. I built one
from an old handbook design years ago and it worked great. Compaired it to
a comercial Crushcraft 11 element beam and also a 6 element home built one,
all at the top of a 40 foot push up pole, one at a time. I used some
stainless steel welding rods for the directors and some fiberglass sticks
about 1/4 inch in diameter for the quad spreaders from those bicycle flags.

On 2/16/2013 1:31 AM, Sal wrote:
I'm building a yagi from the measurement tables the ARRL Antenna Book. I
have the driven element finished and getting a good SWRs with a home-made
gamma match.

I'm going to mount it on a wood 2 X 2 with as many directors as will fit on
an 8 feet boom.

Any advice? (I've already read that a gamma match is a poor choice but it
did work, so we can skip that one. :-)

"Sal"
(KD6VKW)



A gamma match will skew the pattern a bit but that's really nothing to
worry about.

The worry on a gamma match (and most matches) is where the impedance of
the driven element is low, where low is less than 20 ohms.

20 ohms is a number I like, others may like a different number. For
sure if you are down in the 10 or 12 ohm range you are in trouble.

T matches are better, but are more and less complex at the same time.
Personally I use gamma at 6m, both at 2m and T at 70cm.

tom
K0TAR

On Fri, 15 Feb 2013 23:31:52 -0800, "Sal" salmonella@food
poisoning.org wrote:

I'm building a yagi from the measurement tables the ARRL Antenna Book.

Which Antenna Book and which yagi?

I have the driven element finished and getting a good SWRs with a home-made
gamma match.

Think about using a T-match. Slightly better bandwidth and slightly
more symmetrical pattern. However, I will conceded that the Gamma
match (half a T-match) is simpler because it can be driven directly
without a balun.

I prefer a folded dipole driven element (200 ohms) and a 4:1 balun.
With 200 ohms.

I'm going to mount it on a wood 2 X 2 with as many directors as will fit on
an 8 feet boom.

The problem with wood is that it doesn't survive well on top of a
tower. You could paint and preserve it, but by the time you're done,
a metal pipe would probably have been easier. 2x2 also seems a bit
light to support its own weight (plus any birds that may want to
roost). I would suggest a 2x4. Wood is also hygroscopic (absorbs
water), which might have an effect depending on how the antenna is
built.

Drivel: About 15 years ago, I had the semi-bright idea of building an
all wood portable yagi for 440MHz. It was built as if it were a
carpentry project complete with mostly non-metallic joinery. To turn
it into a real antenna, I covered the wooden dowel elements with
aluminum duct tape.
http://www.homedepot.com/Paint-Adhesives-Tape/h_d1/N-5yc1vZ1xhmZarpz/R-100030120/h_d2/ProductDisplay?catalogId=10053#.USBOGfIrFR0
The T-match and balun were attached with U shape staples. Sorry, I
didn't take any photos. After about month of tinkering, I turned it
into firewood. The problem was that trimming this antenna was rather
difficult. As the wood in the elements dried out, the velocity factor
changed, causing the element tuning to change. Of course, I used the
cheapest green lumber I could find, resulting in a continuously
changing VSWR as the wood slowly dried out in the sun. You won't have
that problem if you make only the boom out of wood.

Any advice? (I've already read that a gamma match is a poor choice but it
did work, so we can skip that one. :-)

Measure the 2:1 VSWR bandwidth of the antenna. If it's too narrow to
cover the 220 band, think about using a T-match and balun.

With an 8 foot boom, you'll probably fit 9 elements:
http://www.vk5dj.com/yagi.html
13dBi gain, 44 degree beamwidth.

Idea: I was at the hardware store today and noticed some 2"x3"x10ft
rectangular cross section vinyl rain gutter downspouts. A downspout
might make a usable boom for a yagi.
http://www.lowes.com/pd_12493-322-AW200_4294806370__?productId=1007997
It's quite light, doesn't sag, UV proof, and cheap.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 2/16/2013 9:57 PM, Jeff Liebermann wrote:
On Fri, 15 Feb 2013 23:31:52 -0800, "Sal" salmonella@food
poisoning.org wrote:

I'm building a yagi from the measurement tables the ARRL Antenna Book.

Which Antenna Book and which yagi?

I have the driven element finished and getting a good SWRs with a home-made
gamma match.

Think about using a T-match. Slightly better bandwidth and slightly
more symmetrical pattern. However, I will conceded that the Gamma
match (half a T-match) is simpler because it can be driven directly
without a balun.

I prefer a folded dipole driven element (200 ohms) and a 4:1 balun.
With 200 ohms.

I'm going to mount it on a wood 2 X 2 with as many directors as will fit on
an 8 feet boom.

The problem with wood is that it doesn't survive well on top of a
tower. You could paint and preserve it, but by the time you're done,
a metal pipe would probably have been easier. 2x2 also seems a bit
light to support its own weight (plus any birds that may want to
roost). I would suggest a 2x4. Wood is also hygroscopic (absorbs
water), which might have an effect depending on how the antenna is
built.

Drivel: About 15 years ago, I had the semi-bright idea of building an
all wood portable yagi for 440MHz. It was built as if it were a
carpentry project complete with mostly non-metallic joinery. To turn
it into a real antenna, I covered the wooden dowel elements with
aluminum duct tape.
http://www.homedepot.com/Paint-Adhesives-Tape/h_d1/N-5yc1vZ1xhmZarpz/R-100030120/h_d2/ProductDisplay?catalogId=10053#.USBOGfIrFR0
The T-match and balun were attached with U shape staples. Sorry, I
didn't take any photos. After about month of tinkering, I turned it
into firewood. The problem was that trimming this antenna was rather
difficult. As the wood in the elements dried out, the velocity factor
changed, causing the element tuning to change. Of course, I used the
cheapest green lumber I could find, resulting in a continuously
changing VSWR as the wood slowly dried out in the sun. You won't have
that problem if you make only the boom out of wood.

Any advice? (I've already read that a gamma match is a poor choice but it
did work, so we can skip that one. :-)

Measure the 2:1 VSWR bandwidth of the antenna. If it's too narrow to
cover the 220 band, think about using a T-match and balun.

With an 8 foot boom, you'll probably fit 9 elements:
http://www.vk5dj.com/yagi.html
13dBi gain, 44 degree beamwidth.

Idea: I was at the hardware store today and noticed some 2"x3"x10ft
rectangular cross section vinyl rain gutter downspouts. A downspout
might make a usable boom for a yagi.
http://www.lowes.com/pd_12493-322-AW200_4294806370__?productId=1007997
It's quite light, doesn't sag, UV proof, and cheap.


Nice response.

tom
K0TAR

On Sat, 16 Feb 2013 19:57:44 -0800, Jeff Liebermann
wrote:

With an 8 foot boom, you'll probably fit 9 elements:
http://www.vk5dj.com/yagi.html
13dBi gain, 44 degree beamwidth.

Here's another yagi calculator program:
http://www.yagicad.com/YagiCAD/YagiCAD.htm
It will do a variety of driven elements and yagi styles. It also
exports results to 4NEC2.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 2/16/2013 10:08 AM, Ralph Mowery wrote:
"Sal"salmonella@food poisoning.org wrote in message
...
I'm building a yagi from the measurement tables the ARRL Antenna Book. I
have the driven element finished and getting a good SWRs with a home-made
gamma match.

I'm going to mount it on a wood 2 X 2 with as many directors as will fit
on an 8 feet boom.

Any advice? (I've already read that a gamma match is a poor choice but it
did work, so we can skip that one. :-)


While not what you want to hear, scrap that idea. Look at the Quagi antenna
and a 10 foot piece of the grey plastic electrical conduit. I built one
from an old handbook design years ago and it worked great. Compaired it to
a comercial Crushcraft 11 element beam and also a 6 element home built one,
all at the top of a 40 foot push up pole, one at a time. I used some
stainless steel welding rods for the directors and some fiberglass sticks
about 1/4 inch in diameter for the quad spreaders from those bicycle flags.




I concur! I disassembled my 2 meter quagi antennas and an the process of
building a 222 MHz quagi from using the parts. I also use 1/8 inch
stainless steel welding rods, because I have a bunch of them!

The 2 meter quagi antennas worked great and I expect the 222 antenna to
work well, also.

Paul, KD7HB

On 2/17/2013 12:24 AM, Jeff Liebermann wrote:
On Sat, 16 Feb 2013 19:57:44 -0800, Jeff Liebermann
wrote:

With an 8 foot boom, you'll probably fit 9 elements:
http://www.vk5dj.com/yagi.html
13dBi gain, 44 degree beamwidth.

Here's another yagi calculator program:
http://www.yagicad.com/YagiCAD/YagiCAD.htm
It will do a variety of driven elements and yagi styles. It also
exports results to 4NEC2.



My calculation, based on a database of 100+ EME antennas predicts 13.6
dBi maximum reasonable gain. So that sounds about right.

tom
K0TAR