I am tuning up my homebrew 6-meter yagi and find that the rod inserted into
the capacitor tube of the gamma match is only inserted by about 1-1/2" to
obtain 1:1 SWR. I guesstimated and cut the spacer and shorting bar for the
match to provide about 1-1/2" parallel space between the gamma match and the
driven element. I did this because the text of the article did not specify
the space. Is this dimension critical? Is it normal for a 13" gamma match
to only need 1-1/2" of rod insertion to obtain the proper capacitance?

Thanks.
Russ KG6TDX

if its working then thats where it should be.

gamma match design and tuning includes:
1. distance of shorting bar from center of element
2. space between gamma rod and element
3. diameters of gamma rod and element
4. capacitance added at feed point
5. length of the whole driven element

all 5 factors go into the final match. some are easily changed, like the
capacitance, shorting bar location, and element length. the others are
harder and are usually selected to get in the ballpark and then the easy
ones are adjusted to get the desired match.



"Shadow 998" wrote in message
m...
I am tuning up my homebrew 6-meter yagi and find that the rod inserted
into
the capacitor tube of the gamma match is only inserted by about 1-1/2" to
obtain 1:1 SWR. I guesstimated and cut the spacer and shorting bar for
the
match to provide about 1-1/2" parallel space between the gamma match and
the
driven element. I did this because the text of the article did not
specify
the space. Is this dimension critical? Is it normal for a 13" gamma
match
to only need 1-1/2" of rod insertion to obtain the proper capacitance?

Thanks.
Russ KG6TDX

On Sun, 20 Jun 2004 19:13:09 GMT, "Shadow 998"
wrote:
Is it normal for a 13" gamma match
to only need 1-1/2" of rod insertion to obtain the proper capacitance?

Hi Russ,

It seems I ran across a short hand for the required capacitance for
the common gamma match that offered somewhere between 2pF and 5pf
times the wavelength of the band. That is, 12pF to 30pF - not much
especially if the rod is a close fit with a small dielectric layer.

73's,
Richard Clark, KB7QHC

Richard and Dave, Thanks for the quick responses. It sounds like it is OK
as-is. Using a borrowed MFJ analyzer, I was able to get the SWR literally
flat at 51.9Mhz. The bandwidth is pretty good too: 1.2 @ 50Mhz and maxes
out at 1.7 @ 54Mhz. All in all, I'm quite happy so far.

This is my first attempt at 6 meters and have not made a single contact on
the band since getting my license last year. This year will also be my
first field day which is why I built this beam. Now to figure out if it
has a F/B ratio, forward gain, etc.


Again, Thanks for the help.
Russ (Back to the backyard) ;-)
73 KG6TDX


"Richard Clark" wrote in message
...
On Sun, 20 Jun 2004 19:13:09 GMT, "Shadow 998"
wrote:
Is it normal for a 13" gamma match
to only need 1-1/2" of rod insertion to obtain the proper capacitance?

Hi Russ,

It seems I ran across a short hand for the required capacitance for
the common gamma match that offered somewhere between 2pF and 5pf
times the wavelength of the band. That is, 12pF to 30pF - not much
especially if the rod is a close fit with a small dielectric layer.

73's,
Richard Clark, KB7QHC

On Sun, 20 Jun 2004 22:15:26 GMT, "Shadow 998"
wrote:
This is my first attempt at 6 meters and have not made a single contact on
the band since getting my license last year.

Hi Russ,

You might want to consider if your lack of contacts is due to being
cross polarized with those who you wish to work (or be heard by) - or
using the wrong mode.

73's
Richard Clark, KB7QHC

"Shadow 998" wrote in message
m...

This is my first attempt at 6 meters and have not made a single contact on
the band since getting my license last year. This year will also be my
first field day which is why I built this beam. Now to figure out if it
has a F/B ratio, forward gain, etc.

Your best bet is to listen from about 50.100 to 50.200 on SSB. Calling
frequency is 50.125. East cost was working the West coast earlier today. I
assume the beam is horizontally polarized. Good luck on 6.

Tam/WB2TT FN20

Tam,

Yes, the beam is horizontal, and I finally made two contacts on 50.155 USB
shortly after my last post. I hooked up with two stations; one was about
40 miles away feet on a mountain (he came in @+20 over), the other roughly
80 miles (right in with the noise). Since my antenna is only 8-9 feet above
the ground, it's encouraging.

The F/B ratio seems ok.

Thanks for the response.
Russ
KG6TDX


"Tam/WB2TT" wrote in message
...

"Shadow 998" wrote in message
m...

This is my first attempt at 6 meters and have not made a single contact
on
the band since getting my license last year. This year will also be my
first field day which is why I built this beam. Now to figure out if
it
has a F/B ratio, forward gain, etc.

Your best bet is to listen from about 50.100 to 50.200 on SSB. Calling
frequency is 50.125. East cost was working the West coast earlier today. I
assume the beam is horizontally polarized. Good luck on 6.

Tam/WB2TT FN20

"Shadow 998" wrote in message
om...
Tam,

Yes, the beam is horizontal, and I finally made two contacts on 50.155 USB
shortly after my last post. I hooked up with two stations; one was about
40 miles away feet on a mountain (he came in @+20 over), the other roughly
80 miles (right in with the noise). Since my antenna is only 8-9 feet
above
the ground, it's encouraging.

The F/B ratio seems ok.

Thanks for the response.
Russ
KG6TDX


You did the hard part. Since the antenna is about 1/2 wavelength up, it
should work like gangbuster on 1000 - 1500 mile paths when the band is open.
Oddly, I have worked at least two W0s from here in NJ whose antennas were
strapped to the side of a pickup truck. The 80 mile path will work a lot
better if you can get it about 30 feet up.

Tam/WB2TT

And also, tune between 50.060 and 50.080-- EVEN IF you cant copy cw (this
is the beacon area of 6)
Note frequencies of ANY heard when band NOT open-- IF you hear anything on a
frequency NOT noted,
(unless someone locally has placed a new one on air) Odds are that it is DX
!! that what they there for
to let you know when 6 is open! tho helps is can copy cw, gives you idea
WHERE band open to!
Jim NN7K

--
No trees were killed in the sending of this message. However, a large number
of electrons were terribly inconvenienced !

" People who never get carried away, should be! " --- Malcom Forbes

"Tam/WB2TT" wrote in message
...

"Shadow 998" wrote in message
m...

This is my first attempt at 6 meters and have not made a single contact
on
the band since getting my license last year. This year will also be my
first field day which is why I built this beam. Now to figure out if
it
has a F/B ratio, forward gain, etc.

Your best bet is to listen from about 50.100 to 50.200 on SSB. Calling
frequency is 50.125. East cost was working the West coast earlier today. I
assume the beam is horizontally polarized. Good luck on 6.

Tam/WB2TT FN20

I'm working on CW and can copy a little if it is sloowww. Anyway, the band
opened up this afternoon, and I made my very first DX contact with a QSO
with K7BTZ. He was QRP at 2 watts! I was running in the 50-watt range.

Thanks.

73,
Russ KG6TDX



" wrote in
message ...
And also, tune between 50.060 and 50.080-- EVEN IF you cant copy cw (this
is the beacon area of 6)
Note frequencies of ANY heard when band NOT open-- IF you hear anything on
a
frequency NOT noted,
(unless someone locally has placed a new one on air) Odds are that it is
DX
!! that what they there for
to let you know when 6 is open! tho helps is can copy cw, gives you idea
WHERE band open to!
Jim NN7K

--
No trees were killed in the sending of this message. However, a large
number
of electrons were terribly inconvenienced !

" People who never get carried away, should be! " --- Malcom Forbes

"Tam/WB2TT" wrote in message
...

"Shadow 998" wrote in message
m...

This is my first attempt at 6 meters and have not made a single
contact
on
the band since getting my license last year. This year will also be
my
first field day which is why I built this beam. Now to figure out if
it
has a F/B ratio, forward gain, etc.

Your best bet is to listen from about 50.100 to 50.200 on SSB. Calling
frequency is 50.125. East cost was working the West coast earlier today.
I
assume the beam is horizontally polarized. Good luck on 6.

Tam/WB2TT FN20