Hello all,

I have a 6m transverter on the way this week to use just in time for the
CQWW contest this weekend... one problem NO ANTENNA!!

So I picked up a very old Yagi, built in 1969, but still in great condition.
Its currently cut for the 40 MHz band, so I should be able to trim the
elements down and change the spacing for a 3-element 6m antenna, right?

At any rate, the information I have been able to find so far (from various
Yagi calculators found online such as that found at
http://www.csgnetwork.com/antennae3ycalc.html) give the following figures:

Calculated Driven Side Element Length 4'6 19/32"
Calculated Total Driven Length 9'1 6/32"
Calculated Reflector Length 9'7 5/8"
Calculated Element Spacing 3'7 7/32"
Calculated Director Length 8'6 23/32"

Here are my questions:
1. Can I do this? Cut the elements, change the spacing.
2. What does "driven side element" length refer to? Is this the "matching
dipole" (gamma match) part of the driven element?

Are there any unexpected snags/pitfalls I should look out for?

Thanks,

Jason

"Jason Dugas" wrote in message
...
Hello all,

I have a 6m transverter on the way this week to use just in time for the
CQWW contest this weekend... one problem NO ANTENNA!!

So I picked up a very old Yagi, built in 1969, but still in great
condition.
Its currently cut for the 40 MHz band, so I should be able to trim the
elements down and change the spacing for a 3-element 6m antenna, right?

Jason -

Do you know who made the original Yagi? Is it aluminum tuning or solid rod?

The fastest method is to shorten the reflector, director and driven
elements, BUT
maintain the element spacing. Later - you can look at changing the element
spacing - if desired.

w9gb
--
DO NOT use Reply.
Only reply through ARRL forwarding service to W9GB

The elements are "solid rod" I believe. What are the consequences of not
changing the spacing, while cutting the elements to the right lengths? Loss
of directivity would be my guess, but I'd still have a good radiator with
relatively low SWR?

Thanks,

Jason
"G.Beat" wrote in message
news:NF1Qa.44293$GL4.12054@rwcrnsc53...

"Jason Dugas" wrote in message
...
Hello all,

I have a 6m transverter on the way this week to use just in time for
the
CQWW contest this weekend... one problem NO ANTENNA!!

So I picked up a very old Yagi, built in 1969, but still in great
condition.
Its currently cut for the 40 MHz band, so I should be able to trim the
elements down and change the spacing for a 3-element 6m antenna, right?

Jason -

Do you know who made the original Yagi? Is it aluminum tuning or solid
rod?

The fastest method is to shorten the reflector, director and driven
elements, BUT
maintain the element spacing. Later - you can look at changing the
element
spacing - if desired.

w9gb
--
DO NOT use Reply.
Only reply through ARRL forwarding service to W9GB

"Jason Dugas" wrote in message
...
The elements are "solid rod" I believe. What are the consequences of not
changing the spacing, while cutting the elements to the right lengths?
Loss
of directivity would be my guess, but I'd still have a good radiator with
relatively low SWR?


Jason -

With solid rod elements - you are in a "measure at LEAST twice and cut once"
situation.

Most likely the directive lobe would not be optimized.
You can use antenna modeling software to see the specific results, BUT this
gets you on the air quickly.

w9gb
--
DO NOT use Reply.
Only reply through ARRL forwarding service to W9GB

On or about Sat, 12 Jul 2003 18:03:59 -0500, "Jason Dugas"
wrote about the following in article
:

Hello all,

I have a 6m transverter on the way this week to use just in time for the
CQWW contest this weekend... one problem NO ANTENNA!!

So I picked up a very old Yagi, built in 1969, but still in great condition.
Its currently cut for the 40 MHz band, so I should be able to trim the
elements down and change the spacing for a 3-element 6m antenna, right?

At any rate, the information I have been able to find so far (from various
Yagi calculators found online such as that found at
http://www.csgnetwork.com/antennae3ycalc.html) give the following figures:

Calculated Driven Side Element Length 4'6 19/32"
Calculated Total Driven Length 9'1 6/32"
Calculated Reflector Length 9'7 5/8"
Calculated Element Spacing 3'7 7/32"
Calculated Director Length 8'6 23/32"

Here are my questions:
1. Can I do this? Cut the elements, change the spacing.

Are you sure that it is cut for 40 MHz, and not 40 meters? What service
uses 40 MHz anyway?

If the yagi is really for 40 MHz, then I would just cut the elements to
length and not worry about the spacing, as there is a fairly wide range of
working spacing values. The only thing that would be changed is your
radiation pattern. If the yagi was originally for 40m, you will need to do
a lot of trimming, and will need to adjust the spacing.

2. What does "driven side element" length refer to? Is this the "matching
dipole" (gamma match) part of the driven element?

No, it refers to the length of each leg of the driven element (which is a
dipole)

--
Alex / KC2IVL
ft100 software for Linux http://www.qsl.net/kc2ivl
"Good judgment comes from experience,
and a lot of that comes from bad judgment"

"Alex V Flinsch" wrote in message
news
On or about Sat, 12 Jul 2003 18:03:59 -0500, "Jason Dugas"
wrote about the following in article
:

Hello all,

I have a 6m transverter on the way this week to use just in time for
the
CQWW contest this weekend... one problem NO ANTENNA!!

So I picked up a very old Yagi, built in 1969, but still in great
condition.
Its currently cut for the 40 MHz band, so I should be able to trim the
elements down and change the spacing for a 3-element 6m antenna, right?

At any rate, the information I have been able to find so far (from
various
Yagi calculators found online such as that found at
http://www.csgnetwork.com/antennae3ycalc.html) give the following
figures:

Calculated Driven Side Element Length 4'6 19/32"
Calculated Total Driven Length 9'1 6/32"
Calculated Reflector Length 9'7 5/8"
Calculated Element Spacing 3'7 7/32"
Calculated Director Length 8'6 23/32"

Here are my questions:
1. Can I do this? Cut the elements, change the spacing.

Are you sure that it is cut for 40 MHz, and not 40 meters? What service
uses 40 MHz anyway?

Alex -

40 MHz is within the "Land Mobile" allocation (low band VHF - within 30 to
50 MHz),
which has existed at least since the 1940s (post World War 2).

Here is the NTIA - U.S. Frequency Allocation Chart
http://www.ntia.doc.gov/osmhome/allochrt.html

My father had a commercial radio system at 46 MHz from 1957 to 1990.
The Illinois State Police used 42.xx MHz for their District office stations
for over 50 years
and many of their mobiles (long whip antennas) well into the 1980s and 1990s

Greg
w9gb

"Jason Dugas" wrote in message ...
The elements are "solid rod" I believe. What are the consequences of not
changing the spacing, while cutting the elements to the right lengths? Loss
of directivity would be my guess, but I'd still have a good radiator with
relatively low SWR?

If it were for 40 mhz, the spacing at 50 mhz should be usable as is I
bet. What I'd do is model the antenna with the current spacing, but
with the new element lengths and see what the pattern looks like.
Being the boom is longer on a 40 mhz beam than the 50 mhz, you have
the potential to have a long boom antenna. If the 40 mhz beam was a
"short" maximum f/b ratio antenna, it might be about right on 6m as a
max gain antenna. My 6m beam is 3 elements and copied after the NBS
yagi. The boom is 8 ft long. It's set up for maximum gain and mediocre
f/b ratio. But many people use a 6 ft boom on a 3 el 6m yagi to have
a better f/b ratio with slightly less gain. The spacing is not overly
critical just to operate with decent gain. But you could respace if
you decide to optimise the antenna for your exact wants. My beam is
exactly copied from the one in the elnec or eznec demo. "NBS yagi"
It's 1/2 copper tubing same as the model. The real world results
closely matched what it modeled. MK

"Ralph Mowery" wrote in message
...

I have a 6m transverter on the way this week to use just in time for
the
CQWW contest this weekend... one problem NO ANTENNA!!

So I picked up a very old Yagi, built in 1969, but still in great
condition.
Its currently cut for the 40 MHz band, so I should be able to trim the
elements down and change the spacing for a 3-element 6m antenna, right?


Too late for it now I guess. If you know the frequency of the antenna
then
you can devide it by the frequency you want to operate on and change the
lengths and spacings by the same fraction. Then if gamma matched adjust
the
gamma for a low swr.



Ralph,
You bring up a very valid point-- SCALING! This is an old trick I forgot
about, but I'm certainly glad you mentioned it.

One question-- this antenna has a gamma match-- how does the gamma match
change with respect to all of the other new dimensions?