John Ferrell wrote:
When I assembled it I was disappointed to find it did not have a gamma
match! Instead it got by with a direct connection to the driven
element with the 50 ohm line.

Cushcraft prided themselves on building antennas with a DC resistance of
0 ohms.

In plain English they were static disipators. At their design frequency
they had an impedance of 50 ohms.

When I lived in Philly, we had a sever lightening problem. Whenever there
were lightening storms there were nearby strikes with all sorts of expensive
EMP problems.

When I put up a cushcraft 2m beam (the 11 element vertical polarization on
the same beam as an 11 element horizontal one) with proper gounding they
all "went away". I wonder if our neighbors suddenly noticed next spring that
the lightening had come back :-)

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
I do multitasking. If that bothers you, file a complaint and I will start
ignoring it immediately.

On Jun 20, 10:03*am, John Ferrell wrote:
On Sun, 20 Jun 2010 03:27:52 -0700 (PDT), K1TTT
wrote:





On Jun 16, 5:24 pm, "R.Scott" wrote:
I see all kinds of crazy matching sections in posts about 6 meter
beams. How about direct connect. I have an A4S that has major issues
in the traps and I cant find the problem (IE I opened them and cant
find anything) SOOO I have a new A4S coming.

Has anyone taken an old 3 elem tribander and converted it to 6 meter
monobander using the direct connect.

Any Issues.

Would a 4 elem be better since its a long boom ?

I'm pretty sure I know the answers. Just want to confirm and see if
there is any reason not to direct connect rather than through a
hairpin or a gamma match.

Scotty W7PSK

There are at least 3 reasons to use some kind of a matching network.
1. impedance transformation - usually the feedpoint impedance of a
simple dipole in a yagi is not near 50 ohms so the matching system
gives you an easy way to adjust that.
2. it is often easier to build an aluminum element without a center
insulator and feed it with something like a gamma or T match.
3. to keep current off the feedline shield you need to go from the
unbalanced coax to a balanced dipole feedpoint. *gamma matches and
others do that transformation for you.

I am in agreement with all your points. [Not that I am any kind of
authority!]

Many years back I purchased and installed a Cushcraft A3S tri band
beam with the 40 Meter option. The decision was based on past
experience with Cushcraft products.

When I assembled it I was disappointed to find it did not have a gamma
match! Instead it got by with a direct connection to the driven
element with the 50 ohm line. Then it used a jury rig device called a
"choke balun" to keep the RF where it ought to be... It reminded me of
the Gotham Vertical (Google it!) that so many of us fell for way back
when. I assembled and installed it according to the instructions any
way. Much to my surprise, it worked great! I have been very happy with
it.

That led to my taking the ARRL Antenna course and buying the EZNEC
program. *

Some things I model I can make work and some I cannot.
Some things work I cannot model.
I have concluded that direct connection and gamma matches both work
well.

My cumulative experience is that it is difficult to beat the
commercial products at their game.

OTH, the study and construction of antennas has become one of my
favorite recreational pastimes!

John Ferrell W8CCW- Hide quoted text -

- Show quoted text -

A gamma rod is the easiest thing in the world to build...people who
are scared of 'em just don't understand 'em.

On Jun 20, 5:27*am, K1TTT wrote:
2. it is often easier to build an aluminum element without a center
insulator and feed it with something like a gamma or T match.

Or a folded dipole driven element.
--
73, Cecil, w5dxp.com

On 16.06.2010 20:24, R.Scott wrote:
I see all kinds of crazy matching sections in posts about 6 meter
beams. How about direct connect. I have an A4S that has major issues
in the traps and I cant find the problem (IE I opened them and cant
find anything) SOOO I have a new A4S coming.

Has anyone taken an old 3 elem tribander and converted it to 6 meter
monobander using the direct connect.

Any Issues.

Would a 4 elem be better since its a long boom ?

I'm pretty sure I know the answers. Just want to confirm and see if
there is any reason not to direct connect rather than through a
hairpin or a gamma match.


Scotty W7PSK

Hi

Probably my comments are bit late... but OWA yagi's use direct feed to
driven element with a ferrite balun near the feedpoint.
OWA's give good impedance match in large bandwidth, this is based on
nearer driven element-first director spacing.
Otherwise gain, F/B etc. are very good.
I have constructed one 6m OWA yagi, with 20 ft boom as it was available,
using 7 elements in it, and finally with good match below
S 1.2 between 50...51 MHz.
Nothing critical in it, element dimensions were taken from NW3Z & WA3FET
article in OWA yagis, their 21MHz desing was re-scaled to 50MHz.
At least waterproofing is less critical in direct feed.

73's Kari

On Thu, 26 Aug 2010 13:38:22 +0300, KBa wrote:

On 16.06.2010 20:24, R.Scott wrote:
I see all kinds of crazy matching sections in posts about 6 meter
beams. How about direct connect.

Direct connect is used in a number of tribanders, but AFAIK it's not
used in larger than 3L beams due to the low impedance. It can also
distort the pattern, but with a 3L I doubt you'd notice. Just put 3
or 4 2.4", #32 mix toroids with 4 or 5 turns of feed line through
them. It'll give the isolation and balance needed as long as the
impedance at the feed point is correct.

I have an A4S that has major issues
in the traps and I cant find the problem (IE I opened them and cant

Problems in traps can be difficult to find. I had an ATB34 that
appeared to have a trap problem but it turned out to be the feed line
to driven element connection. They use 1/4-20 SS bolts through the
insulators. The bolts simply press on the element inside the
insulator. One was making a poor connection even though it felt
tight. Taking it apart and cleaning the ends of the bolts and
polishing the ends of the driven element where the bolts rested fixed
it even though I could see nothing wrong at the time.

find anything) SOOO I have a new A4S coming.

Has anyone taken an old 3 elem tribander and converted it to 6 meter
monobander using the direct connect.

Any Issues.

Spacing is generally far more than a little too wide.


Would a 4 elem be better since its a long boom ?

Long boom? Tribanders come in a wide variety of lengths. If it's the
typical 19 or 20', you are probably looking at around 5 elements.

Use one of the modeling programs, or get some to run it for you.


I'm pretty sure I know the answers. Just want to confirm and see if
there is any reason not to direct connect rather than through a
hairpin or a gamma match.

There's really nothing particularly complicated about a hairpin or
gamma match. There are probably lots of designs that could be copied.



Scotty W7PSK

Hi

Probably my comments are bit late... but OWA yagi's use direct feed to
driven element with a ferrite balun near the feedpoint.
OWA's give good impedance match in large bandwidth, this is based on
nearer driven element-first director spacing.
Otherwise gain, F/B etc. are very good.
I have constructed one 6m OWA yagi, with 20 ft boom as it was available,
using 7 elements in it, and finally with good match below

That's enough elements for a 30 foot boom.

S 1.2 between 50...51 MHz.
Nothing critical in it, element dimensions were taken from NW3Z & WA3FET
article in OWA yagis, their 21MHz desing was re-scaled to 50MHz.
At least waterproofing is less critical in direct feed.

Water proofing the coax is very important, particularly when you get
to 50 MHz.

73

Roger (K8RI)


73's Kari