<< In a message dated 9/30/01 11:28:01 AM Pacific Daylight Time,
n9rla@yahoo.com writes: <<
Hello All,
I have an unusual antenna project in mind and could use some direction.
I'm planning to build a "short yagi" for 6 meters. I've gone through my
limited collection of reference books, and haven't found much help. I
have
several editions of the Handbook, a fairly extensive QST collection, and a
94 edition of the ARRL Antenna Book. I've been considering some of the
Antenna compendium series, is there a particular issue that discusses
loaded
yagis? I'm sure they are all great, but can't afford to buy the whole
series.
What I have in mind is a two or three element 6 meter yagi on a 6' boom.
I
want to keep the element lengths less than 6' overall. At 6 meters, I
think this should still produce a reasonably efficient antenna. I realize
that most people don't need to reduce the size of a 6 meter yagi, so I
don't
expect to find "cook book" directions.
And while I'm at it, what do you guys think about loading methods? Anyone
care to comment on loading coils versus linear loading?
Thanks, Dan
Dan Evans N9RLA
Scottsburg, IN 47170
{EM78}
IN-Ham list administrator
QRP-l #1269
1/2 of the N9RLA /R no budget Rover Team
Check out the Rover Resource Page at:
http://www.qsl.net/n9rla
>>
Any project has some merrit. I honestly can't find any here loading 6M
elements based on building beams for a long time as has Jiri OK1RI doubting
the increased trouble and less performance. I'd forget the loading as you
will need a fair test set up to tune the loading elements for pattern and it
will end up taking many hours unless you really know what you are doing. A
6M beam is already small so why waste the effort and complicate the design?
Unless you find an artcile with specific data on such beam you have a
problem. See Communications Quarterally Winter/98 by W1JR who had very good
results with his version.
AntenneX has a great 3 element quad (no loading coils) in their Qct issue
with great pictures. Give that a try also. They used a lathe to make parts
but you can duplicate it with a wood drill and wooden or fiberglass 3/8"
dowels and a 2x2" wooden boom for the economy model.
In your version you would need special insulators to hold the loading
whatever it is as well as the elements. Very few have any of this hardware.
You will have an increased number of joints/element. You need to be intimate
on feed systems and their adjustments and the main goal should be there isn't
any RF spill over down the coax shield.
I built a couple of 6M full size 5 element beams on a 16' boom based on a
proven design of 10.5 dBI & 25 dB F/B and used a special feed system. I had
all the hardware from many other projects and tubing from Boeing Surplus. I
used a continious diameter 5/8"X.028" tubing progressively beefed up in the
center--inside. There were NO ELEMENT JOINTS. It hasn't required any
electrical or mechanical maintenance in 9 years. I clean the feedpoint
connections once in awhile. Since I used different tubing than the original
W8CC model, I had to use Eznec to finalize the lengths back when computers
weren't so fast--many hours and hours. It also has a very interesting
"double dip SWR curve" which I've observed only on this yagi. This has great
possibilities--stay tuned. Both beams still work great but it took a
lifetime of experience to do it better than I could buy. The aluminum cost
in this case was a few bucks but the Computer, Mill, Lathe time and
Satisfaction of building it and using it was very very high.
Back in 1947 I had ideas of making a 10M wire beam somehow using bamboo or
something to hold the wire. Fortunately an Elmer friend straightened me out
and told me to forget this total nonsense and buy the Hy-Lite 3 element 10M
beam advertised for $19.95. It used stand off insulators to hold the
elements on the twin boom. It took about 15 minutes to assemble and about 5
minutes to install on a 10' tower (with PP motor) on the roof. This is
somewhat of an assembly and installation record. That later was changed to a
single boom "Plumbers Delight" construction.
Now after spending "Many Big Bucks" collecting aluminum tubing over the years
so I could save all kinds of $$$ building my own, I'm here to tell you
that's a "Total Myth. I had to build special racks to hold it also. I'd be
very happy if I could sell my stock pile of aluminum as it's the most
expensive mistake one can make if you think you are going to save money.
Even with all this tubing there will be a size, length and quantity you just
don't have at times. Quads use fiberglass rods that only have to be strong
enough and only the copper wire size is critical for size and is available in
small steps at a low cost--in particular for scaling. Forget trying to scale
tubing for test models.
I've tried just about every beam configurations there is which all this
available tubing and hardware I've made permitted me to do. Big Deal! I
purchased a Big Lathe and Mill to assist and it saved a lot of time. At one
time it was perhaps justified for the serious antenna man. Forget about it
now. I've uncovered some very effective concepts I use some would like to
know about real bad. They can't afford them!
The cost of aluminum is so high now for small purchases you can't afford to
build a beam and the technical concepts for the average Appliance Operator
are beyond his reach. There is a simple solution:
There are Antenna Manufacturers out there like M2, Antenna Mart & Raibeam
that have can provide you a well made beam of Hi-Tech Mechanical and
Electrical Design you can't duplicate for "love nor money." M2's beams
designs are so good even I copied them. Of course it ended up costing me
many many times more. I only had the advantage of being able to add what I
thought I couldn't live without for whatever it was worth. One DE was a FD
set for 100 ohms that was fed with balanced 100 ohm coax into a Johnson Match
Box Tuner. It works great on any beam.
I've operated 2 years of the last 5 on 6M running 100W in SD using a 2
element quad I made in an hour. It's 25' high fed with 100 ohm balanced coax
into a 6M version of the Match Box. It worked great but then like the old
days I ran the coax directly into the balanced link and series Xc of a HA6
Transverter-modified. I made hundreds of contacts even holding a frequency
for as along as 3-4 hours of one contact after another from one coast to the
other time after time. It was like being on a DX Pedition in a reasonably
rare grid square. With great audio they got the call correct each time when
I stated it "just once per QSO." 2 element beams work great at 25' on 6M and
should be a standard antenna for 6M. I suggest 3, 5 and more elements
starting at 50-100'.
Here is what I would suggest for today that will save you a fortune in money
and time. I even follow my own advice. I wanted to try the Raibeam 6M 2
element on a 2' boom weighing about 3 lbs for the 25' antenna and the Raibeam
Butt Kicker 5 Element Beam on a 23.5' boom I've repeatedly heard others using
on 6M. They stood out on 6M repeatedly and I had to find out for myself even
thought I knew all the technical details having discussed them with Chuck
Smith of Raibeam over the last 5 or so years.
So I spend the money for 2 of the 2 elements and the 5 element on a 23' boom
(first time for a yagi since 1947). It was one of the best investments I
ever made even though I could have perhaps duplicated it with a lot of time.
>From box to installed on the tower for all 3 beams took a couple of hours all
alone. It dominated 6M with 100W like I have never before even with the W8CC
5 element beam. The details will be in 73 Mag along with a Front Cover
Picture showing the 5 element along with 2-2 element beams vertically
polarized about 8' apart and 10' below. I ran polarization shift tests and
gained the advantage of reduced QSB on 6M that can be very active at times
and on other bands.
The 2 element Raibeam will do about what the 2 element quad will do at 25'.
I'd give it or a 2 element quad a try but you will really need a 100 ohm
balanced feedline for a quad and connected to a Match Box in the shack for
the best results. For 2 element the Z is around 70-100 ohms depending how it
is tuned. From box to tower shouldn't take over an hour and you are in for
"Immediate Success" on the air. No time design delays.
I just saved you a big chuck of money and time. I will humbly accept all
forms of money, stocks and bonds for your appreciation hi. k7gco
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