Compact 40m gain antenna
 

I have a coworker that would like to put up a 40m antenna on his tower
that has some gain and directivity. I have modeled a few things, and
while they are fairly satisfactory, I wanted to see what ideas the group
had.

The approximate limitations are as follows -

o Boomlength 30 feet
o Element length 30 feet
o Any vertical components are max -10 feet from the plane of the boom
and elements. The reason here is that it's a crankup, and his roof
clearance would be about 10 feet when lowered.

It would be desirable to have both CW and phone covered, but phone only
is ok.
It will need to be coax fed.

Thanks.

tom
K0TAR

Tom Ring wrote:

I have a coworker that would like to put up a 40m antenna on his tower
that has some gain and directivity. I have modeled a few things, and
while they are fairly satisfactory, I wanted to see what ideas the group
had.

The approximate limitations are as follows -

o Boomlength 30 feet
o Element length 30 feet
o Any vertical components are max -10 feet from the plane of the boom
and elements. The reason here is that it's a crankup, and his roof
clearance would be about 10 feet when lowered.

It would be desirable to have both CW and phone covered, but phone only
is ok.
It will need to be coax fed.

Thanks.

tom
K0TAR

So, no ideas? At all? I thought better of the group.

Tom Ring wrote:
Tom Ring wrote:

I have a coworker that would like to put up a 40m antenna on his
tower
that has some gain and directivity. I have modeled a few things,
and
while they are fairly satisfactory, I wanted to see what ideas the
group
had.

The approximate limitations are as follows -

o Boomlength 30 feet
o Element length 30 feet
o Any vertical components are max -10 feet from the plane of the
boom
and elements. The reason here is that it's a crankup, and his roof

clearance would be about 10 feet when lowered.

It would be desirable to have both CW and phone covered, but phone
only
is ok.
It will need to be coax fed.

Thanks.

tom
K0TAR

So, no ideas? At all? I thought better of the group.
You are asking near impossibility, that is why there was no response.
QST had an Article on short, loaded beams, and W4RNL has written an
excellent Article on the same. Check those out.
Are you wanting to build or buy? This group, whom you don't think
much of, is mostly about design and building.
Gary N4AST

Hi Tom,

In article , you say...
I haven't asked anything impossible or even tough, since I only gave a
general bound on size, gave the rough band limits desired, and said we'd
like gain and directivity.

Well... :-)

On a band that has a bandwidth of roughly 4% of
its center frequency, you're going to be REALLY
hard-pressed to get coverage of both phone and
CW on an antenna that is a little over 40% of
full size. So far, no manufacturer has been
able to come up with the antenna you describe.

Many years ago, Swan Antennas had a 2-element
40 meter beam that used half size elements.
As I recall, it used loading coils midway
through each element. I'm not very sure, but
I think the boom length was about 16 feet.
I think they got somewhere around 100 kHz
between 2:1 points. That wouldn't even cover
the entire phone band, and the elements are
longer than your design requirements.

So, yes, you are asking for something very tough,
if not impossible.

But, I wish you good luck in your quest! :-)

73,
Bob

--
+----------------------------------------------+
| Bob Schreibmaier K3PH | E-mail: |
| Kresgeville, PA 18333 | http://www.dxis.org |
+----------------------------------------------+

Bob Schreibmaier wrote:

Hi Tom,

In article , you say...

I haven't asked anything impossible or even tough, since I only gave a
general bound on size, gave the rough band limits desired, and said we'd
like gain and directivity.


Well... :-)

On a band that has a bandwidth of roughly 4% of
its center frequency, you're going to be REALLY
hard-pressed to get coverage of both phone and
CW on an antenna that is a little over 40% of
full size. So far, no manufacturer has been
able to come up with the antenna you describe.

Many years ago, Swan Antennas had a 2-element
40 meter beam that used half size elements.
As I recall, it used loading coils midway
through each element. I'm not very sure, but
I think the boom length was about 16 feet.
I think they got somewhere around 100 kHz
between 2:1 points. That wouldn't even cover
the entire phone band, and the elements are
longer than your design requirements.

So, yes, you are asking for something very tough,
if not impossible.

But, I wish you good luck in your quest! :-)

73,
Bob



And also from my original post

"o Boomlength 30 feet
o Element length 30 feet "

which is a whole lot more than 16 feet.

But you are probably correct. It's impossible.

"Tom Ring" wrote in message
.. .
Bob Schreibmaier wrote:

Hi Tom,

In article , you say...

I haven't asked anything impossible or even tough, since I only gave a
general bound on size, gave the rough band limits desired, and said we'd
like gain and directivity.


Well... :-)

On a band that has a bandwidth of roughly 4% of
its center frequency, you're going to be REALLY
hard-pressed to get coverage of both phone and
CW on an antenna that is a little over 40% of
full size. So far, no manufacturer has been
able to come up with the antenna you describe.

Many years ago, Swan Antennas had a 2-element
40 meter beam that used half size elements.
As I recall, it used loading coils midway
through each element. I'm not very sure, but
I think the boom length was about 16 feet.
I think they got somewhere around 100 kHz
between 2:1 points. That wouldn't even cover
the entire phone band, and the elements are
longer than your design requirements.

So, yes, you are asking for something very tough,
if not impossible.

But, I wish you good luck in your quest! :-)

73,
Bob



And also from my original post

"o Boomlength 30 feet
o Element length 30 feet "

which is a whole lot more than 16 feet.

But you are probably correct. It's impossible.


Check out the Optibeam Moxon rectangle. I think its boom length is something
like 20 feet. Also, the Moxon Antenna Project web site has a program for
calculating the various dimensions.

Paul AB0SI

You can model this with EZNEC:

Get 2 Cushcraft 40M rotating dipoles and a boom to hold them. Tune the
dipoles separately to 7 MHz. Put them on the boom, observe operating
results, and adjust the driven element to your favorite 40M slot. The
elements interact, so the reflector may require adjustment as well, to keep
it around 7 MHZ when you adjust the driven element.
--
73, Dave, N3HE
Cincinnati OH

"Tom Ring" wrote in message
.. .
Tom Ring wrote:

I have a coworker that would like to put up a 40m antenna on his tower
that has some gain and directivity. I have modeled a few things, and

Is remote tuning an option?

Thinking helically loaded elements with an adjustable piece of short
metal pipe around each element half, or a metal rod inside the turns .
Move the pipe(s) towards or away from the feedpoint/centre. Using string
of course!

Could also put an adjustable C across the feedpoint?

Cheers Bob VK2YQA


Bob


From my original post -

"It would be desirable to have both CW and phone covered, but phone only
is ok."

tom
K0TAR

Smaller then a yagi but similar gains,

the moxon could be a solution.

http://www.cebik.com/moxon/moxpage.html


Tom wrote:

I have a coworker that would like to put up a 40m antenna on his tower
that has some gain and directivity. I have modeled a few things, and
while they are fairly satisfactory, I wanted to see what ideas the group
had.

The approximate limitations are as follows -

o Boomlength 30 feet
o Element length 30 feet
o Any vertical components are max -10 feet from the plane of the boom
and elements. The reason here is that it's a crankup, and his roof
clearance would be about 10 feet when lowered.

It would be desirable to have both CW and phone covered, but phone only
is ok.
It will need to be coax fed.

Thanks.

tom
K0TAR