Hi..

I wish to build shorty dipoles for 20 and 80 meters and have considered coil
loaded but dismissed them as too narrow band so i`m considering linear
loading
for b/width and space ...(my garden is 14ft x 35ft )...

I find my homebrew magloops r/x very well but don`t t/x too good!!! hence
the need for a larger directional ant on the rotator without encroaching on
neighbours space ....(too much) .... ;o)

I have googled, but there isn`t much info available and what there is, is a
little
too technical for me to take in.. /

Is anyone familiar with the merits (or otherwise) + information and s/ware
for
designing and building said antennae ?? all help and pointers welcome.

Thanks..

Len....G6ZSG.....

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I got some pretty good search results when I Googled "linear loaded
antenna". You have to put the phrase in quotes to get best results. My
search yielded about 193 results.

There's an antenna called the "Cobra Junior"
www.vk1od.net/cobra/index.htm that may be of interest.

Of course Cibek has a very technical discussion of various loaded
antennas. I usually just read the last paragraph summaries to find out
what he's driving at. www.cebik.com/gp/linvert1.html

Here's a good short description of linear loading - I believe the ASCII
graphic is accidentally end-wrapped. lists.contesting.com/_topband/2002
09/msg00030.html

Here's a description of a portable linear loading antenna:
http://www.io.com/~n5fc/notebk_ant.htm that seems good for moderate
distances.

73
--
MGFoster:::mgf00 at earthlink decimal-point net
Oakland, CA (USA)
** Respond only to this newsgroup. I DO NOT respond to emails **

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Lee wrote:
Hi..

I wish to build shorty dipoles for 20 and 80 meters and have considered coil
loaded but dismissed them as too narrow band so i`m considering linear
loading
for b/width and space ...(my garden is 14ft x 35ft )...

I find my homebrew magloops r/x very well but don`t t/x too good!!! hence
the need for a larger directional ant on the rotator without encroaching on
neighbours space ....(too much) .... ;o)

I have googled, but there isn`t much info available and what there is, is a
little
too technical for me to take in.. /

Is anyone familiar with the merits (or otherwise) + information and s/ware
for
designing and building said antennae ?? all help and pointers welcome.

"MGFoster" wrote in message
...
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Hash: SHA1

I got some pretty good search results when I Googled "linear loaded
antenna". You have to put the phrase in quotes to get best results. My
search yielded about 193 results.

Yes, thanks i did the same with the same result except that i didn`t use
quotes .... i`ll try that anyway...
The results i got weren`t very helpfull, i did a search of this NG....

There's an antenna called the "Cobra Junior"
www.vk1od.net/cobra/index.htm that may be of interest.

Yes i saw that, very nice.

Of course Cibek has a very technical discussion of various loaded
antennas. I usually just read the last paragraph summaries to find out
what he's driving at. www.cebik.com/gp/linvert1.html

That`s where i have problems.

Here's a good short description of linear loading - I believe the ASCII
graphic is accidentally end-wrapped. lists.contesting.com/_topband/2002
09/msg00030.html

Here's a description of a portable linear loading antenna:
http://www.io.com/~n5fc/notebk_ant.htm that seems good for moderate
distances.

I wish to build single band dipoles not needing an atu......
I was thinking along the lines of a 28meg dipole with loading wires to 20
meters
below the main element spaced approx 6 inches as a starter, along the lines
of a
shortened vertical.......

Thanks for reply.

Cheers..

Len ....G6ZSG.......

On 18 Jan, 04:36, "Lee" wrote:
"MGFoster" wrote in message

...

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Hash: SHA1

I got some pretty good search results when I Googled "linear loaded
antenna". *You have to put the phrase in quotes to get best results. *My
search yielded about 193 results.

Yes, thanks i did the same with the same result except that i didn`t use
quotes .... i`ll try that anyway...
The results i got weren`t very helpfull, i did a search of this NG....

There's an antenna called the "Cobra Junior"
www.vk1od.net/cobra/index.htmthat may be of interest.

Yes i saw that, very nice.

Of course Cibek has a very technical discussion of various loaded
antennas. *I usually just read the last paragraph summaries to find out
what he's driving at. *www.cebik.com/gp/linvert1.html

That`s where i have problems.

Here's a good short description of linear loading - I believe the ASCII
graphic is accidentally end-wrapped. *lists.contesting.com/_topband/2002
09/msg00030.html

Here's a description of a portable linear loading antenna:
http://www.io.com/~n5fc/notebk_ant.htmthat seems good for moderate
distances.

I wish to build single band dipoles not needing an atu......
I was thinking along the lines of a 28meg dipole with loading wires to 20
meters
below the main element spaced approx 6 inches as a starter, along the lines
of a
shortened vertical.......

Thanks for reply.

Cheers..

Len ....G6ZSG.......

LEE.
First get a hoola hoop from ASDA or a hose pipewith which you can make
your own

Get a similar diameter former and wind wire on it close wound first in
one direction and then reverse the windings on top of the first
windings. Slide this on the hula hoop and then stretch it out like a
fish net. The length of the wire must equal or exceed the wave length
of the frequency required. You have two wire ends at the same point
with which you can supply power. The wound wire is infact a loop
circuit of its own and you can stretch it out using a MFJ 259 until
you hit the sweet spot. Impedance will be around 20+ ohms which
increases with the number of wavelengths used Note that the inductance
is cancelled by the reverse turns and the capacitance is cancelled by
the cross winding.Tho the antenna covers little area apurture is
covered by gain, the loop with its inherrant gapaqcitive positioning
creates an electric field that extends beyond its physical shape. You
see this effect in a mobile when the audio increases as you drive by
power lines and the like.
Cheers and beers
Art Unwin KB9MZ....XG (uk)

"art" wrote
Tho the antenna covers little area apurture is covered by gain, the loop
with its inherrant gapaqcitive positioning creates an electric field that
extends beyond its physical shape. You see this effect in a mobile when the
audio increases as you drive by
power lines and the like.
______________

More likely it is due to the collection and re-radiation of fields by nearby
conductors, so as to increase the net field arriving at the mobile antenna.

RF

On 18 Jan, 07:21, "Richard Fry" wrote:
"art" *wroteTho the antenna covers little area apurture is covered by gain, the loop
with its inherrant gapaqcitive positioning creates an electric field that
extends beyond its physical shape. You see this effect in a mobile when the
audio increases as you drive by

power lines and the like.
______________

More likely it is due to the collection and re-radiation of fields by nearby
conductors, so as to increase the net field arriving at the mobile antenna..

RF

Exactly. The antennas electrical field is larger than its physical
size.

On Fri, 18 Jan 2008 07:59:37 GMT, "Lee"
wrote:

I find my homebrew magloops r/x very well but don`t t/x too good!!! hence
the need for a larger directional ant on the rotator without encroaching on
neighbours space ....(too much) .... ;o)

Hi Lee,

I presume you mean by maploops, those that are only a meter or so in
diameter. You need a larger loop for 80M. A simple one turn with
plenty of surface area and low Ohmic contacts is preferred as anything
more complex invites massive loss.

The law with small antennas is their Radiation Resistance in relation
to their Ohmic Resistance. Most would grab some #12 wire and shrug it
off without a thought. That lack of thought generates calories in
heat. Some would add wire turns, the proximity of them merely
multiplies the heat, not the signal.

Either way the tune up seems great, but the results are miserable (no
doubt the source of your statement above). A good low band loop will
have a sharp tuning (narrow bandwidth). A poor low band loop will
appear to exhibit a great SWR for a broad bandwidth, You can test
this yourself with almost no effort at all.

Let's take that one meter diameter loop that is available from several
commercial outlets, and instead build it your self with house wire
(#12). The Radiation Resistance in the 80M band will be 528
millionths of an Ohm, Copper loss will be 16 thousandths of an Ohm
(not counting skin effect) - we still haven't computed connection
issues. Already, your copper loss is thirty times the radiation
resistance - I will let you delve into the issues of efficiency.

Doubling that loop diameter will double the copper loss to 32
thousandths of an Ohm, but what happens to Radiation Resistance? It
now runs more to 8 thousandths of an Ohm. The ratio has dropped from
30:1 to 4:1 in this doubling of size - even when the resistance of the
wire grew, the Radiation Resistance grew faster. Efficiency increases
dramatically.

Increase the loop size and use a larger conductor.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Fri, 18 Jan 2008 07:59:37 GMT, "Lee"

Hi Lee,

I presume you mean by maploops, those that are only a meter or so in
diameter. You need a larger loop for 80M. A simple one turn with
plenty of surface area and low Ohmic contacts is preferred as anything
more complex invites massive loss.

The law with small antennas is their Radiation Resistance in relation
to their Ohmic Resistance. Most would grab some #12 wire and shrug it
off without a thought. That lack of thought generates calories in
heat. Some would add wire turns, the proximity of them merely
multiplies the heat, not the signal.

Either way the tune up seems great, but the results are miserable (no
doubt the source of your statement above). A good low band loop will
have a sharp tuning (narrow bandwidth). A poor low band loop will
appear to exhibit a great SWR for a broad bandwidth, You can test
this yourself with almost no effort at all.

Let's take that one meter diameter loop that is available from several
commercial outlets, and instead build it your self with house wire
(#12). The Radiation Resistance in the 80M band will be 528
millionths of an Ohm, Copper loss will be 16 thousandths of an Ohm
(not counting skin effect) - we still haven't computed connection
issues. Already, your copper loss is thirty times the radiation
resistance - I will let you delve into the issues of efficiency.

Doubling that loop diameter will double the copper loss to 32
thousandths of an Ohm, but what happens to Radiation Resistance? It
now runs more to 8 thousandths of an Ohm. The ratio has dropped from
30:1 to 4:1 in this doubling of size - even when the resistance of the
wire grew, the Radiation Resistance grew faster. Efficiency increases
dramatically.

Increase the loop size and use a larger conductor.

73's
Richard Clark, KB7QHC

Hi! Richard.

Yes, I already have a 3ft dia magloop 3-30megs also a 5ft square
magloop for 14-80megs..... both cover the 14meg band....
they work extremely well. and as they are virtually noiseles i hear
stations that can`t be heard on a regular wideband antenna
due to a better sn ratio, albeit, at reduced signal strength.....also,
unfortunately, with reduced transmission levels.....
( very good listening antennas ).

That`s why i need a larger, lower `Q` antenna ....which will also
fit in my garden space to t/x on.....

I like 20 meters a lot running Slowscan, Hampal and Digital Voice.

Regards..

Len....G6ZSG......

On Sat, 19 Jan 2008 09:22:43 GMT, "Lee"
wrote:

Yes, I already have a 3ft dia magloop 3-30megs also a 5ft square
magloop for 14-80megs..... both cover the 14meg band....
they work extremely well. and as they are virtually noiseles i hear
stations that can`t be heard on a regular wideband antenna
due to a better sn ratio, albeit, at reduced signal strength.....also,
unfortunately, with reduced transmission levels.....
( very good listening antennas ).

Hi Len (Lee?),

Are these commercial loops with substantial conductors (well beyond
what would be called wire)? If so, then pushing them into 80M is
going to be a trick unless the 3-30MHz model in fact works. If it
does not, it needs more capacitance, and that is going to be a loss
leader if you try to add any.

The only other limitation in the 20M band would be how high are they?

That`s why i need a larger, lower `Q` antenna ....which will also
fit in my garden space to t/x on.....

I like 20 meters a lot running Slowscan, Hampal and Digital Voice.

As far as 20M goes, your garden is long enough for a conventional
dipole - provided you have the support, and the direction favors your
need. If not, it seems unlikely you will gain anything over the
magloops. (Go for more height.)

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sat, 19 Jan 2008 09:22:43 GMT, "Lee"
wrote:

Yes, I already have a 3ft dia magloop 3-30megs

also a 5ft square magloop for 14-80megs

Typo should read - magloop for 14 - 3.5megs ( can go lower at higher `Q` )

..... both cover the 14meg band....


they work extremely well. and as they are virtually noiseles i hear
stations that can`t be heard on a regular wideband antenna
due to a better sn ratio, albeit, at reduced signal strength.....also,
unfortunately, with reduced transmission levels.....
( very good listening antennas ).

Hi Len (Lee?),

Len, Lee Leon Leonard or Leonardo .....no problem as the birth name is
Leonard...

Are these commercial loops with substantial conductors (well beyond
what would be called wire)?

HOMEBREW!!! .....3ft dia loop, ( 10 ft circumference ) 3/8" tube -
can be persuaded to 80meters ....
HOMEBREW!!! ......5`.0" square ( 20ft circumference ) loop 3/4" tube -
can persuade it to 160meters.

If so, then pushing them into 80M is

No problem....80meters isn`t the problem ! - they work!

going to be a trick unless the 3-30MHz model in fact works.

It works well in the design freq of 3 - 30 megs....can work lower at higher
`Q`
........higher `Q` not good!

If it does not, it needs more capacitance, and that is going to be a loss
leader if you try to add any.

Agreed.

The only other limitation in the 20M band would be how high are they?

Vertical - ground level for vertically polarised ground wave- with
directivity.
Horizontal - 30ft for horizontal `omni directional` polarization - less
gain
than a straight, horizontal dipole at the same height.

That`s why i need a larger, lower `Q` antenna ....which will also
fit in my garden space to t/x on.....

I like 20 meters a lot running Slowscan, Hampal and Digital Voice.

As far as 20M goes, your garden is long enough for a conventional
dipole - provided you have the support, and the direction favors your
need. If not, it seems unlikely you will gain anything over the
magloops.

(Go for more height.)

If you read the o/p, you wouldn`t question everything i have already
stated Richard!!!

I don`t want a fixed dipole at low height!! i want a rotary dipole on the
top
of my tower (mast)....i am aware i can fit a 33foot fixed, wire dipole into
a
35foot garden, lengthwise, but the length of my garden runs east/west so the
dipole would fire north/south - not good...... the magloops receive very
well,
with lower noise than a regular antenna, i can hear stations i wouldn`t
normally
hear on a regular antenna, plus, a horizontal dipole, generally, has more
gain
than a horizontal omni magloop at the same height but is a noisier r/x than
the
magloop, which makes the dipole better for t/x mode....Yes?...
My garden is 14ft wide and a 14meg dipole is 33ft+, i don`t want my
neighbours
complaining when half the antenna is over their garden when i`m working east
west...hence linear loading the dipole...to shorten it!!

All i requested was a suitable design configuration for a linear loaded
halfsize
rotary dipole to go on top of the tower and my reasons why.......
not a discussion on magloops ....

I`ll go with the linear short 1/4 wave vertical layout for each leg of the
dipole,
where half the element is fed back on itself down to 6 inches from the
ground
( or, in my case, to the mast ) with about 3 inch spacing of the element.

Regards.

Len ....( Lee, Leon Leonard Leonardo ).........G6ZSG....