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....

On Sun, 20 Jan 2008 01:36:22 GMT, "Lee"
wrote:

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?...

Hi Len,

Yes, but marginally. This is a double edged sword. The Q that gives
you such superlative receive characteristics is going to drive you
into CW mode in, perhaps, 80M, and certainly in 160M - not to speak of
the critical tuning. You have the height, something I missed from the
distraction of 20 other unrelated postings to this thread, so you have
solutions and that height is both far and away sufficient for the
upper HF, and more to the matter, the best practical solution for your
neighborhood. As to the antenna construction, you have answered the
Ohmic losses to a considerable extent, and you are aware of the
relationship of Ohmic Loss to Radiation Resistance. You would do well
to report to the group your SWR bandwidth for several of these bands
so we can get a grasp of the actual Q. Simply for 160/80/40/20, how
many KHz between the 2:1 points?

There are a lot of pluses there, except for the high Q on low bands.
You also express in your list of negatives that you don't seem to get
out (a transmit problem).

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!!

If I recall (as you have a lot of widely separate issues here), you
want to operate 20M. Your garden as you state here is too narrow (it
is) for the direction you desire. An efficient design is going to
demand end loading aka top hat style (long radial spokes at the end of
each arm of the dipole you want).The end loads, if sufficiently
developed (and not a simple installation, I suspect) could do it
without further loading with a coil somewhere (and if it were
anywhere, the good advice from years of reporting here would indicate
that it would be one half to two thirds out and away from the feed
point, on both sides). Another alternative is an inverted V which
would seem to be within your capacity (depends on where the tower is
sited).

As your interests span 20 down to 80 and Q intrudes into the bandwidth
you desire at the longer wavelengths, then lowering Q would only drive
down your efficiency and increase your complaint of getting out. It
seems you are rapidly moving away from the loops. You might (if you
can interpret the technical comments) try Arthur's contra-wound
inventions. No doubt, they too would make good receive antennas, and
the proximity of windings would lower Q, but this would come at a
severe loss of gain and sensitivity. A receiver has enough gain to
make up for this loss, but your transmitter is forever crippled with
the introduction of both Ohmic loss and its loss boost due to tightly
coupled currents.

A larger diameter antenna is called for if you are sticking with
loops, but that is probably unmanageable.

Another breed of loop, the halfwave open loop allows you to build an
omni horizontal polarized antenna in a small area, but we now enter
into other issues you have not discussed. What resources, other than
the tower, are available to you for supporting the linear loaded
dipole you seek? If you have four support points, your garden size is
not unsuited to a full half wave design, there are no Q issues, no
efficiency issues - except for matching to a 5 Ohm load. What can I
say? Compromise antennas demand care and feeding.


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.

You lost me entirely here. You want a horizontal dipole, and you will
build a closely coupled vertical system that will rotate where half
the element is within 6 inches of ground? Too much is left unsaid in
this description. Is your tower guyed? Freestanding? You are using
the mast (tower?) as half the antenna? Is the mast (tower?) grounded?

This sounds like you are top feeding a vertical quarterwave open
transmission line that rotates around one element. If so, your feed
line is going to really become a nightmare of isolation. It will show
varying horizontal/vertical directivity to a loss of 10dB in any
direction - if you can match to the near short circuit conditions at
the feed point.

I don't think this is what you mean, but what you describe is vague.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 20 Jan 2008 01:36:22 GMT, "Lee"
wrote:

As your interests span 20 down to 80

Only 20......

and Q intrudes into the bandwidth
you desire at the longer wavelengths, then lowering Q would only drive
down your efficiency and increase your complaint of getting out. It
seems you are rapidly moving away from the loops. You might (if you
can interpret the technical comments) try Arthur's contra-wound
inventions. No doubt, they too would make good receive antennas, and
the proximity of windings would lower Q, but this would come at a
severe loss of gain and sensitivity. A receiver has enough gain to
make up for this loss, but your transmitter is forever crippled with
the introduction of both Ohmic loss and its loss boost due to tightly
coupled currents.

A larger diameter antenna is called for if you are sticking with
loops, but that is probably unmanageable.

20 foot circumference is the longest magloop for 14megs operation!!!
That is with 90% efficiency...

Another breed of loop, the halfwave open loop allows you to build an
omni horizontal polarized antenna in a small area, but we now enter
into other issues you have not discussed. What resources, other than
the tower, are available to you for supporting the linear loaded
dipole you seek?

None

If you have four support points, your garden size is
not unsuited to a full half wave design, there are no Q issues, no
efficiency issues - except for matching to a 5 Ohm load. What can I
say? Compromise antennas demand care and feeding.


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.

You lost me entirely here. You want a horizontal dipole, and you will
build a closely coupled vertical system that will rotate where half
the element is within 6 inches of ground? Too much is left unsaid in
this description. Is your tower guyed? Freestanding? You are using
the mast (tower?) as half the antenna? Is the mast (tower?) grounded?

This sounds like you are top feeding a vertical quarterwave open
transmission line that rotates around one element. If so, your feed
line is going to really become a nightmare of isolation. It will show
varying horizontal/vertical directivity to a loss of 10dB in any
direction - if you can match to the near short circuit conditions at
the feed point.

I`m not building a vertical !!!

I don't think this is what you mean, but what you describe is vague.

Probably.
Imagine a half wave dipole with each leg folded back on itself
effectively becoming half its original physical length but still
the original electrical length, each leg is like a long thin letter
`U` ..like a folded dipole that has been cut open circuit opposite
the feed point...I shouldn`t have mentioned a vertical because
it mis-lead you, it was meant just to describe the configuration
of the dipole legs.

Cheers.

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

On Sun, 20 Jan 2008 04:22:40 GMT, "Lee"
wrote:

I don't think this is what you mean, but what you describe is vague.

Probably.
Imagine a half wave dipole with each leg folded back on itself
effectively becoming half its original physical length but still
the original electrical length, each leg is like a long thin letter
`U` ..like a folded dipole that has been cut open circuit opposite
the feed point...I shouldn`t have mentioned a vertical because
it mis-lead you, it was meant just to describe the configuration
of the dipole legs.

Hi Len,

This is more tenable. A satisfactory dipole, no horrendous loss due
to counter winding feed. If you can hoist a beam, about 19 feet wide,
with two wires connected at the ends and returning below it about 4
inches coming back within 4 inches of the beam above; then you stand a
chance, provided you can match to about a 7 Ohm load.

I presume your description follows something like (in fixed font):

_____________________________0____________________ __________
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73's
Richard Clark, KB7QHC