On 2/17/2013 7:51 PM, tom wrote:

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

tom
K0TAR


Here is a link to a table of a lot of high performance yagis.

http://www.sm2cew.com/gt.htm

tom
K0TAR

"tom" wrote in message
. ..
On 2/17/2013 7:51 PM, tom wrote:

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

tom
K0TAR


Here is a link to a table of a lot of high performance yagis.

http://www.sm2cew.com/gt.htm

tom
K0TAR



Thank you all for your thoughtful comments. I like the downspout idea. (I
was going to coat the wood boom with good epoxy paint, but, considering also
the weight issue, maybe I should go with the downspout. It's going on a
chimney mount, not a tower, making maintenance a bit simpler.)

I saw the T-match but never intended to try it. I did get my gamma match to
a 1.2:1 VSWR so, now I'm undecided.

I used to use YAGICAD running under a BASIC interpreter, I think, but a
lo-o-ong time ago. I will have a fresh look at it.

I thought after the first four or five directors were in place, their
spacing wouldn't be affected by adding more directors. Thanks for the
heads-up that it matters.

"Sal"

"Jeff Liebermann" wrote in message
...
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

"Jeff Liebermann" wrote in message
...
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?

snip

Jeff, I have the 18th Edition of the ARRL Antenna Book, copyright 1997.

I'm in Chapter 18, titled "VHF and UHF Antenna Systems." I'm using Table
16, titled "Dimensions for 16-element 3.9-wavelength 222-MHz Yagi."

I'm bugged by something else I'm seeing. Table 16 specifies a 664 mm driven
element (DE) It's longer than the DE of other construction articles. Most
articles call for something between 645 and 648 mm. (Example: On the same
page as Table 16, I see also Table 14, "Free-Space Dimensions for the
222-MHz Yagi Family." It gives a DE of 647 mm.)

Something is indisputably okay. My prototype DE (664 mm) is hanging by
strings above my bench and I'm getting a 1.2:1 - 1.3:1 with a short length
of cable. I can hit a repeater 15 miles away with one watt without even
turning my DE vertical. Too bad neither of my analyzers works at 222.

Yes, I fully expect the match to need adjusting after I add parasitic
elements. The road from here-to-there has so many branches!

"Sal"

On Sat, 23 Feb 2013 17:07:31 -0800, "Sal" salmonella@food
poisoning.org wrote:


"Jeff Liebermann" wrote in message
.. .
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?

snip

Jeff, I have the 18th Edition of the ARRL Antenna Book, copyright 1997.
I'm in Chapter 18, titled "VHF and UHF Antenna Systems." I'm using Table
16, titled "Dimensions for 16-element 3.9-wavelength 222-MHz Yagi."

I have the 19th edition. Same table on Pg 18-31.

I'm bugged by something else I'm seeing. Table 16 specifies a 664 mm driven
element (DE) It's longer than the DE of other construction articles. Most
articles call for something between 645 and 648 mm. (Example: On the same
page as Table 16, I see also Table 14, "Free-Space Dimensions for the
222-MHz Yagi Family." It gives a DE of 647 mm.)

That's easy. Both antennas have elements connected to the aluminum
boom (except for the driven element). Looks like the boom diameters
are different. When the elements are connected to the boom in this
manner, the boom becomes part of the element in that the conduction
path now goes around the boom. This tends to shorten the element
lengths. All the various yagi designer programs can include the boom
diameter in their calculations. I strongly suggest that unless you're
building EXACTLY what's in the article, that you use one of the
programs previous mentioned to grind the numbers correctly.

In addition, I have a suggestion. If you're using a solid rod for the
elements, round off the ends to a hemispherical radius. Use 1/2 the
distance between the base of the radius and the peak for the element
end point. If you're using hollow tubing, you can also cram a big
rivet or screw into the end to get the same rounded effect. This will
increase your usable bandwidth.

Something is indisputably okay. My prototype DE (664 mm) is hanging by
strings above my bench and I'm getting a 1.2:1 - 1.3:1 with a short length
of cable. I can hit a repeater 15 miles away with one watt without even
turning my DE vertical. Too bad neither of my analyzers works at 222.

Please note that you also get 1:1 with a dummy load. You can also
match just about anything with your gamma match. Tune the antenna for
gain, bandwidth, and/or F/B ratio. VSWR is easy to fix.

Also VSWR is not as important as pattern and gain. You can get
perfect VSWR, and have the signal sprayed all over the place. If you
look at the antenna patterns on the same pages as the tables, you'll
see that even with a properly designed antenna, you have a rather
strange and skewed pattern. Incidentally, T-match and balun should
fix the funny pattern.

Yes, I fully expect the match to need adjusting after I add parasitic
elements. The road from here-to-there has so many branches!

Not really. The first 4 or 5 elements are what provides the VSWR. Try
waving additional elements around the front of the antenna notice how
little the VSWR changes. However, the gain, directivity, and F/B
ratio certainly will be affected.

As for your lack of an antenna analyzer, this is actually a good
thing. What you really want to do is see what the antenna is doing
over a wide range of frequencies. For that, I suggest a return loss
bridge. I use a Telonic Rho-tector Model TRB-50 and a Texscan RCB-3.
Here's what's inside:
http://www.qsl.net/n9zia/rlb/texscan.png
Both will go from 0.5MHz to 1GHz. All you need is a decent RF sweep
generator, oscilloscope, terminators, and cables. You can see the
VSWR curve over the frequency range while you're tuning. You can also
do the same thing with a directional coupler and a diode detector, but
I think the return loss bridge is easier. I've also built a few for
microwave frequencies (2.4 and 5.7GHz).



--
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 2/23/2013 9:33 PM, Jeff Liebermann wrote:
On Sat, 23 Feb 2013 17:07:31 -0800, "Sal" salmonella@food
poisoning.org wrote:


"Jeff Liebermann" wrote in message
...
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?

snip

Jeff, I have the 18th Edition of the ARRL Antenna Book, copyright 1997.
I'm in Chapter 18, titled "VHF and UHF Antenna Systems." I'm using Table
16, titled "Dimensions for 16-element 3.9-wavelength 222-MHz Yagi."

I have the 19th edition. Same table on Pg 18-31.

I'm bugged by something else I'm seeing. Table 16 specifies a 664 mm driven
element (DE) It's longer than the DE of other construction articles. Most
articles call for something between 645 and 648 mm. (Example: On the same
page as Table 16, I see also Table 14, "Free-Space Dimensions for the
222-MHz Yagi Family." It gives a DE of 647 mm.)

That's easy. Both antennas have elements connected to the aluminum
boom (except for the driven element). Looks like the boom diameters
are different. When the elements are connected to the boom in this
manner, the boom becomes part of the element in that the conduction
path now goes around the boom. This tends to shorten the element
lengths. All the various yagi designer programs can include the boom
diameter in their calculations. I strongly suggest that unless you're
building EXACTLY what's in the article, that you use one of the
programs previous mentioned to grind the numbers correctly.

In addition, I have a suggestion. If you're using a solid rod for the
elements, round off the ends to a hemispherical radius. Use 1/2 the
distance between the base of the radius and the peak for the element
end point. If you're using hollow tubing, you can also cram a big
rivet or screw into the end to get the same rounded effect. This will
increase your usable bandwidth.

Something is indisputably okay. My prototype DE (664 mm) is hanging by
strings above my bench and I'm getting a 1.2:1 - 1.3:1 with a short length
of cable. I can hit a repeater 15 miles away with one watt without even
turning my DE vertical. Too bad neither of my analyzers works at 222.

Please note that you also get 1:1 with a dummy load. You can also
match just about anything with your gamma match. Tune the antenna for
gain, bandwidth, and/or F/B ratio. VSWR is easy to fix.

Also VSWR is not as important as pattern and gain. You can get
perfect VSWR, and have the signal sprayed all over the place. If you
look at the antenna patterns on the same pages as the tables, you'll
see that even with a properly designed antenna, you have a rather
strange and skewed pattern. Incidentally, T-match and balun should
fix the funny pattern.

Yes, I fully expect the match to need adjusting after I add parasitic
elements. The road from here-to-there has so many branches!

Not really. The first 4 or 5 elements are what provides the VSWR. Try
waving additional elements around the front of the antenna notice how
little the VSWR changes. However, the gain, directivity, and F/B
ratio certainly will be affected.

As for your lack of an antenna analyzer, this is actually a good
thing. What you really want to do is see what the antenna is doing
over a wide range of frequencies. For that, I suggest a return loss
bridge. I use a Telonic Rho-tector Model TRB-50 and a Texscan RCB-3.
Here's what's inside:
http://www.qsl.net/n9zia/rlb/texscan.png
Both will go from 0.5MHz to 1GHz. All you need is a decent RF sweep
generator, oscilloscope, terminators, and cables. You can see the
VSWR curve over the frequency range while you're tuning. You can also
do the same thing with a directional coupler and a diode detector, but
I think the return loss bridge is easier. I've also built a few for
microwave frequencies (2.4 and 5.7GHz).




One thing to remember is you generally do not want elements that are
electrically connected to the boom. The connection is usually not very
good and eventually corrodes. This makes the antenna detune in an
unpredictable manner.

That said, you can weld elements to the boom, which works.

You are better off using insulated elements with inserts in the boom
holes such as Delrin.

This will change the correction factor, but that is a known.

tom
K0TAR

"Jeff Liebermann" wrote in message
...


snip

As for your lack of an antenna analyzer, this is actually a good
thing. What you really want to do is see what the antenna is doing
over a wide range of frequencies. For that, I suggest a return loss
bridge. I use a Telonic Rho-tector Model TRB-50 and a Texscan RCB-3.
Here's what's inside:
http://www.qsl.net/n9zia/rlb/texscan.png
Both will go from 0.5MHz to 1GHz. All you need is a decent RF sweep
generator, oscilloscope, terminators, and cables. You can see the
VSWR curve over the frequency range while you're tuning. You can also
do the same thing with a directional coupler and a diode detector, but
I think the return loss bridge is easier. I've also built a few for
microwave frequencies (2.4 and 5.7GHz).

I have the o'scope and a sweep generator/ spectrum analyzer combination to
provide the RF. I'd have to check to see if the generator provides a sweep
signal for the scope's external horizontal input.

The bridge looks like a one-evening project although I might have to
hand-make those 1% resistors.

By the way, I found a way of using the sweeper/spec-an combination as a
crude antenna checker. I loop the generator directly into the analyzer, but
use a T-connector at one of the ports. Of, course, it produces a clean,
flat line. Next, if I connect an unterminated length of cable to the
T-connector, I see a comb pattern produced by reflected energy. (The comb's
appearance is dependent on the length of the cable and the test setup.)
Lastly, with an antenna on the end of the cable, the comb goes flat at the
frequency (ies) where the antenna is radiating ... reduced reflections at
some freqs since the antenna is radiating most of the forward power. It's
an interesting effect to observe but not sensitive enough for much more than
a GO/NOGO check.

If I put the T-connector at the antenna, itself, with one cable each to the
sweeper/spec-an, the pattern changes somewhat but I haven't analyzed what I
see.

"Sal"

"tom" wrote in message
. ..

snip

One thing to remember is you generally do not want elements that are
electrically connected to the boom. The connection is usually not very
good and eventually corrodes. This makes the antenna detune in an
unpredictable manner.

That said, you can weld elements to the boom, which works.

You are better off using insulated elements with inserts in the boom holes
such as Delrin.

This will change the correction factor, but that is a known.

tom
K0TAR


At the moment, my driven element is 664 mm of half-inch copper pipe, my
favorite medium for VHF/UHF antennas. I made some antennas for the RACES
station at the local firehouse about fifteen years ago and they're still up
there.

If I were to continue in that vein, I could weld (torch solder, really) the
elements to a longer piece of copper pipe.

I have seen the "known" correction factors referenced in vague terms, but
nothing that I ever got my arms around. Where should I be looking?

"Sal"
(KD6VKW)

On 2/23/2013 11:41 PM, Sal wrote:


At the moment, my driven element is 664 mm of half-inch copper pipe, my
favorite medium for VHF/UHF antennas. I made some antennas for the RACES
station at the local firehouse about fifteen years ago and they're still up
there.

If I were to continue in that vein, I could weld (torch solder, really) the
elements to a longer piece of copper pipe.

I have seen the "known" correction factors referenced in vague terms, but
nothing that I ever got my arms around. Where should I be looking?

"Sal"
(KD6VKW)



A good source is VE7BQH, Lionel. He has a lot of info related to EME
antennas that are as well engineered as possible for obvious reasons.

I've never looked at his correction factors as I have ones for through
the boom insulated that I know work for my build type. My corrections
are from WB0TEM.

What bands are you building for?

Here's a link to some of Lionel's information at SM2CEW. If you need to
correspond with him, contact me directly and I'll get you his email.

http://www.sm2cew.com/gt.htm

tom
K0TAR

On 2/24/2013 8:43 PM, tom wrote:
On 2/23/2013 11:41 PM, Sal wrote:


At the moment, my driven element is 664 mm of half-inch copper pipe, my
favorite medium for VHF/UHF antennas. I made some antennas for the RACES
station at the local firehouse about fifteen years ago and they're
still up
there.

If I were to continue in that vein, I could weld (torch solder,
really) the
elements to a longer piece of copper pipe.

I have seen the "known" correction factors referenced in vague terms, but
nothing that I ever got my arms around. Where should I be looking?

"Sal"
(KD6VKW)



A good source is VE7BQH, Lionel. He has a lot of info related to EME
antennas that are as well engineered as possible for obvious reasons.

I've never looked at his correction factors as I have ones for through
the boom insulated that I know work for my build type. My corrections
are from WB0TEM.

What bands are you building for?

Here's a link to some of Lionel's information at SM2CEW. If you need to
correspond with him, contact me directly and I'll get you his email.

http://www.sm2cew.com/gt.htm

tom
K0TAR


I've done some searching for corrections for through the boom
uninsulated and found that the opinion is that it's not a good idea.
And it makes sense if you read why - the current is really high at the
center of the element and any variation in contact resistance to the
boom or material will change the result.

What you would like is the result to be based on only the insulated
element conductance and the shielding of the boom, which is easier to
calculate and less variable.

tom
K0TAR