Art Unwin wrote:

...
Seems to me you are recommending the "?slinky" !
Is that correct?
Art

I believe, he is speaking of rotating the flat surfaces of the
conductor(s) 90 degrees to what a "slinkys'" orientation places them at.

In which case, "mondo-capacitive loading to the 'environment'" is also
introduced ... while minimizing capacitive loading between turns.

Regards,
JS

On Nov 21, 9:52*am, John Smith wrote:
Art Unwin wrote:
...
Seems to me you are recommending the "?slinky" !
Is that correct?
Art

I believe, he is speaking of rotating the flat surfaces of the
conductor(s) 90 degrees to what a "slinkys'" orientation places them at.

In which case, "mondo-capacitive loading to the 'environment'" is also
introduced ... while minimizing capacitive loading between turns.

Regards,
JS

Wouldn't that take more room than a slinky per turn?
His attic is very small!.I think he would be much better placing the
turns as close together as possible
to obtain axial directivity. The only mod required to the slinky is to
ensure the number of right hand turn loop
are equal to the number of left hand turned loops. Feed could still
be at the center and depending on the amount
of wire used it would radiate like a dipole or axially. What this does
is cancel the lumped loads created in manufacture which
Wim suggests is a problem ie the two supposedly lumped loads will
cancel
such that you have several wavelengths of wire helix style and no or
repetitive points of none reactive impedances. He could ofcourse
place
the windings in a vertical direction to obtain an omnidirectional
pattern and utilise the available room to a maximum.
A lot depends on what frequencies he wishes to use as to what form the
radiator becomes.
Best regards
Art

On Nov 21, 10:51*am, Art Unwin wrote:
On Nov 21, 9:52*am, John Smith wrote:

Art Unwin wrote:
...
Seems to me you are recommending the "?slinky" !
Is that correct?
Art

I believe, he is speaking of rotating the flat surfaces of the
conductor(s) 90 degrees to what a "slinkys'" orientation places them at..

In which case, "mondo-capacitive loading to the 'environment'" is also
introduced ... while minimizing capacitive loading between turns.

Regards,
JS

Wouldn't that take more room than a slinky per turn?
His attic is very small!.I think he would be much better placing the
turns as close together as possible
to obtain axial directivity. The only mod required to the slinky is to
ensure the number of right hand turn loop
are equal to the number of left *hand turned loops. Feed could still
be at the center and depending on the amount
of wire used it would radiate like a dipole or axially. What this does
is cancel the lumped loads created in manufacture which
Wim suggests is a problem ie the two supposedly lumped loads will
cancel
*such that you have several wavelengths of wire helix style and no or
repetitive points of none *reactive impedances. He could ofcourse
place
the windings in a vertical direction to obtain an omnidirectional
pattern and utilise the available room to a maximum.
A lot depends on what frequencies he wishes to use as to what form the
radiator becomes.
Best regards
Art

I forgot to mention that a similar type radiator is shown in Antenna
Applications
Reference Guide by Johnson and Jasik with slight modification. This
design was succeeded by the helix antenna
to obtain circular polarization which is now universal with respect to
space communications.
The beauty of this design is the multiplicity of resonant points and
the use of different frequencies.
The economy of space is some what altered by the need of multi
wavelength of wire because
of slow wave.but then it enables axial directivity. There are many
hams who are delighted by the slinky performance
and they are still sold in huge numbers to the ham community, so it
must be performing!
Art Unwin

Art Unwin wrote:

...
Wouldn't that take more room than a slinky per turn?
His attic is very small!.I think he would be much better placing the
turns as close together as possible
to obtain axial directivity. The only mod required to the slinky is to
ensure the number of right hand turn loop
are equal to the number of left hand turned loops. Feed could still
be at the center and depending on the amount
of wire used it would radiate like a dipole or axially. What this does
is cancel the lumped loads created in manufacture which
Wim suggests is a problem ie the two supposedly lumped loads will
cancel
such that you have several wavelengths of wire helix style and no or
repetitive points of none reactive impedances. He could ofcourse
place
the windings in a vertical direction to obtain an omnidirectional
pattern and utilise the available room to a maximum.
A lot depends on what frequencies he wishes to use as to what form the
radiator becomes.
Best regards
Art

Art:

The way I "read" him is, he now has a 1m loop, SINGLE TURN (equiv. to
resonating a 8-12+ ft. whip on the hf bands?) able to do 10-30m--with
WHATEVER "matchbox" he is choosing to run ... he is contemplating on
adding a second 1m turn (to add 40m capabilities, apparently) ... are we
on the same page? ... and, loops are NEVER omni-directional! Well,
other than one constructed to radiate/receive in the plane of the loop
and run in a horizontal plane, would, perhaps, do some type of
omni-horizontal-polarization?--and a 1m at 10-30m, it ain't such an
animal! (well, maybe-kinda-sorta, but I DON'T KNOW! I would have to get
hands-on-experience before trusting a ventured reply ... any books I
have ever laid hands on are vague on all this ... )

Personally, the only time I have ever used a loop is for AM broadcast
radio and direction finding (fox hunts) in the 10 to 2m bands, and, I
did NOT want omni capabilities! ... well, there may have been one or
two--but so long ago they escape memory ... I never did "like them."

Or, in other words, I am NOT a "loop guru" ... :-(

Anyway, after all that verbiage, the cut-to-the-chase: "I would think a
slinky and what he has are two 'different species'."

Regards,
JS

On 21 nov, 16:44, Art Unwin wrote:
On Nov 21, 5:38*am, Wimpie wrote:



On 21 nov, 04:47, Steve wrote:

I've seen several programs that will help you calculate the precise
dimensions of a single-turn loop, given the composition of the
radiating element, its thickness, and so on. However, none of these
programs are written to cover the case of a two or more-turn loop.

Does anyone know of a program that will offer guidance in the
construction of a two or more-turn loop?

Thanks,

Steve

Hello Steve,

You probably did some loop calculations and found that in a transmit
case the voltage across the tuning capacitor is very high (and
bandwidth is limited). Also for small loops, most input power is lost
as heat due to copper resistance.

When you make a two turn loop, the radiation resistance will increase
with factor 4. So with half the current through the loop, the radiated
power is same (as for a single turn loop). *When the 2 turns of the
loop are relative close together, the inductance increases with factor
4, hence the reactance.

The current has been halved, but because of the reactance, the voltage
across the tuning capacitance will be 2 times the value for the single
turn loop with higher probability on corona effects. *An advantage can
be an almost 4 times smaller tuning capacitor.

One may expect that the loss resistance due to heat of a two-turn
inductor will be twice as high (w.r.t. single turn case). This is not
true; the loss resistance will be more then twice as high because of
proximity effect. The current will not equally distribute along the
circumference of the tube/wire. *So the efficiency of the loop will be
less then twice as high (w.r.t. single turn case).

When the turns are far apart (with respect to wire/tube diameter),
inductance will not be 4 times higher and proximity effect will be
less. You will get better performance than the single turn loop made
of same diameter tube/wire. The result will be the same as when you
place the two turns in parallel. Inductance will decrease somewhat
(hence lower voltage across capacitor), AC resistance also, hence
radiation efficiency).

There is an "however". When you make a single turn loop from flat
strip that has the same width as the length of your two-turn loop, you
will notice: *1. reduced AC resistance (because of the significantly
larger circumference of the flat strip with respect to a thin round
tube, 2. inductance will decrease (H field lines have to take a longer
path around the wide strip), 3. radiation resistance will not change
with respect to a single turn loop from wire/tube.
This results in higher efficiency and increased bandwidth. * The
overall result will be better then for your two-turn loop. I think
that is the reason why most programs are for single turn loops.

So for the transmit case, given fixed diameter of your loop, the
larger the copper surface (=length*circumference), the better the
efficiency. *Best thing to enhance conductor surface is to use very
wide flat strip (high wind load), or multiple wires (with some spacing
in between) in parallel (limited wind load).

Off course for the receive-only case, a multi turn loop can be helpful
as you can use a smaller tuning capacitor.

Best regards,

Wim
PA3DJSwww.tetech.nl
In case of PM, don't forget to remove abc.

Seems to me you are recommending the "?slinky" !
Is that correct?
Art

Sorry Art, I am not talking about a slinky.

I am just talking about a multi turn (2 turns) loop where overall wire
length is 0.25 lambda so you can assume that current in wire is
constant along the length. It must be tuned by external capacitance.

Regarding the strip. When you take a 3.14m long 20cm wide thin copper
strip and make a loop of it (1m diameter), it will have a better
efficiency then when you take 6.28m copper tubing with Dtube=2cm and
make a two-turn loop (Dloop=1m, turns 18 cm apart).

In the strip case, the current has more circumference to flow (40cm)
instead of 6.28cm for the copper tubing. AC resistance of copper
tubing will be about 10 times higher. Off course, current in two-turn
loop will be half (for same radiated power), but still heat losses
will be 10*0.5^2=2.5 times higher (for the two-turn loop).

When both loops have good efficiency (so radiation resistance
dominates), the strip loop will have better bandwidth as flux path is
longer and therefore results in less inductance.

I hope this clarifies my posting.

Best regards,

Wim
PA3DJS
Please remove abc in case of PM.

On Nov 21, 5:18*pm, Wimpie wrote:
On 21 nov, 16:44, Art Unwin wrote:



On Nov 21, 5:38*am, Wimpie wrote:

On 21 nov, 04:47, Steve wrote:

I've seen several programs that will help you calculate the precise
dimensions of a single-turn loop, given the composition of the
radiating element, its thickness, and so on. However, none of these
programs are written to cover the case of a two or more-turn loop.

Does anyone know of a program that will offer guidance in the
construction of a two or more-turn loop?

Thanks,

Steve

Hello Steve,

You probably did some loop calculations and found that in a transmit
case the voltage across the tuning capacitor is very high (and
bandwidth is limited). Also for small loops, most input power is lost
as heat due to copper resistance.

When you make a two turn loop, the radiation resistance will increase
with factor 4. So with half the current through the loop, the radiated
power is same (as for a single turn loop). *When the 2 turns of the
loop are relative close together, the inductance increases with factor
4, hence the reactance.

The current has been halved, but because of the reactance, the voltage
across the tuning capacitance will be 2 times the value for the single
turn loop with higher probability on corona effects. *An advantage can
be an almost 4 times smaller tuning capacitor.

One may expect that the loss resistance due to heat of a two-turn
inductor will be twice as high (w.r.t. single turn case). This is not
true; the loss resistance will be more then twice as high because of
proximity effect. The current will not equally distribute along the
circumference of the tube/wire. *So the efficiency of the loop will be
less then twice as high (w.r.t. single turn case).

When the turns are far apart (with respect to wire/tube diameter),
inductance will not be 4 times higher and proximity effect will be
less. You will get better performance than the single turn loop made
of same diameter tube/wire. The result will be the same as when you
place the two turns in parallel. Inductance will decrease somewhat
(hence lower voltage across capacitor), AC resistance also, hence
radiation efficiency).

There is an "however". When you make a single turn loop from flat
strip that has the same width as the length of your two-turn loop, you
will notice: *1. reduced AC resistance (because of the significantly
larger circumference of the flat strip with respect to a thin round
tube, 2. inductance will decrease (H field lines have to take a longer
path around the wide strip), 3. radiation resistance will not change
with respect to a single turn loop from wire/tube.
This results in higher efficiency and increased bandwidth. * The
overall result will be better then for your two-turn loop. I think
that is the reason why most programs are for single turn loops.

So for the transmit case, given fixed diameter of your loop, the
larger the copper surface (=length*circumference), the better the
efficiency. *Best thing to enhance conductor surface is to use very
wide flat strip (high wind load), or multiple wires (with some spacing
in between) in parallel (limited wind load).

Off course for the receive-only case, a multi turn loop can be helpful
as you can use a smaller tuning capacitor.

Best regards,

Wim
PA3DJSwww.tetech.nl
In case of PM, don't forget to remove abc.

Seems to me you are recommending the "?slinky" !
Is that correct?
Art

Sorry Art, I am not talking about a slinky.

I am just talking about a multi turn (2 turns) loop where overall wire
length is 0.25 lambda so you can assume that current in wire is
constant along the length. It must be tuned by external capacitance.

Regarding the strip. When you take a 3.14m long 20cm wide thin copper
strip and make a loop of it (1m diameter), it will have a better
efficiency then when you take 6.28m *copper tubing with Dtube=2cm and
make a two-turn loop (Dloop=1m, turns 18 cm apart).

In the strip case, the current has more circumference to flow (40cm)
instead of 6.28cm for the copper tubing. *AC resistance of copper
tubing will be about 10 times higher. Off course, current in two-turn
loop will be half (for same radiated power), but still heat losses
will be 10*0.5^2=2.5 times higher (for the two-turn loop).

When both loops have good efficiency (so radiation resistance
dominates), the strip loop will have better bandwidth as flux path is
longer and therefore results in less inductance.

I hope this clarifies my posting.

Best regards,

Wim
PA3DJS
Please remove abc in case of PM.

I think I am missing something Wim. A slinky has a strip winding that
is edge wound which provides the largest disparity
between the inside radius and the outside radius. On one of the top
transmitters the inductance winding is such that the inner radius
is close to the outside radius. Naturally the different pitch of the
windings is very different as is the inter coil capacitance.
As Roy stated charges accumulate on sharp edges which I see as correct
but I cannot see how that alteres the diference all that much as the
same clearance is required So in the final analysis for less
inductance which form is which., the longer inductance or the shorter
inductance on the assumption that the number of turns are similara nd
I can acceptt your word for it? I referred to a slinky purely to
emphasize the importance of reverse windings so that lumped loadings
applied are cancelled. Actually the modern slinky is not contra wound
for some reason but I assume that is for the novelty movement reasons
for children and not because of radiation reasons. The slinky patent
is now defunct if that matters and iI am assuming that the fed would
be centre fed.
Thank you so much for responding
Best regards
Art

Wimpie wrote:
. . .
There is an "however". When you make a single turn loop from flat
strip that has the same width as the length of your two-turn loop, you
will notice: 1. reduced AC resistance (because of the significantly
larger circumference of the flat strip with respect to a thin round
tube, 2. inductance will decrease (H field lines have to take a longer
path around the wide strip), 3. radiation resistance will not change
with respect to a single turn loop from wire/tube.
This results in higher efficiency and increased bandwidth. The
overall result will be better then for your two-turn loop. I think
that is the reason why most programs are for single turn loops.

So for the transmit case, given fixed diameter of your loop, the
larger the copper surface (=length*circumference), the better the
efficiency. Best thing to enhance conductor surface is to use very
wide flat strip (high wind load), or multiple wires (with some spacing
in between) in parallel (limited wind load).
. . .

Flat conductors aren't as attractive as they look at first glance. The
problem is the same proximity effect mentioned earlier in the posting.
Current is distributed evenly around a round conductor (assuming the
perimeter is a very small fraction of a wavelength), but not along a
flat strip. Because of proximity effect, the current is much more
concentrated near the edges than at the middle. The result is that the
resistance is considerably higher than for a wire with the same surface
area. In figuring an "equivalent diameter" of a thin flat strip in order
to get the same L and C properties, the rule is that a strip is
equivalent to a wire whose diameter is half the strip width. This means
that a strip of width w or total "circumference" 2 * w is equivalent to
a wire with a circumference of pi * w / 2 ~ 1.6 w, in so far as L and C
go. Since the same phenomenon affects the inductance and resistance,
this would also be a good working rule for estimating the relative R of
a strip or wire.

Roy Lewallen, W7EL

On Fri, 21 Nov 2008 18:24:20 -0800, Roy Lewallen
wrote:

Flat conductors aren't as attractive as they look at first glance. The
problem is the same proximity effect mentioned earlier in the posting.
Current is distributed evenly around a round conductor (assuming the
perimeter is a very small fraction of a wavelength), but not along a
flat strip. Because of proximity effect, the current is much more
concentrated near the edges than at the middle. The result is that the
resistance is considerably higher than for a wire with the same surface
area. In figuring an "equivalent diameter" of a thin flat strip in order
to get the same L and C properties, the rule is that a strip is
equivalent to a wire whose diameter is half the strip width. This means
that a strip of width w or total "circumference" 2 * w is equivalent to
a wire with a circumference of pi * w / 2 ~ 1.6 w, in so far as L and C
go. Since the same phenomenon affects the inductance and resistance,
this would also be a good working rule for estimating the relative R of
a strip or wire.

Roy Lewallen, W7EL

Thanks. I think you just explained the cause of a problem I fought in
about 1980. I had "designed" a 930MHz yagi antenna for a utility
telemetry system. In order to cut system costs, I decided to build
the antenna from stamped 0.062" aluminum. My initial dimensions were
stolen from a Scala yagi which used approximately 0.500" diameter
round rods for elements. I reasoned that to obtain the same
bandwidth, I would need to use the same circumference as the rod. That
made the initial prototypes elements 0.8" wide. After some tweaking,
the antenna tuned to the correct center frequency, but the 2:1 VSWR
bandwidth was much less than the original Scala antenna.

So, I increased the width of the stamped elements (with aluminum duct
tape) until the bandwidth improved. I landed at 1.25" or 2.5 times
the width of the rod elements, somewhat larger than the recommended
2.0 times the rod diameter.

However, when I added a coined stiffener groove to the stamped "boom"
and elements, the bandwidth increased again, to much more than
necessary. After the usual all night cut-n-try session, I landed on
2.0 times the width of the rod elements, with the coined stiffeners,
which apparently increased the effective diameter of the elements.

Coining the "boom" also wrecked all the element tuning since it
increases their effective end to end length by the depth of the
coining. I had a hell of a time dealing with the sheet metal vendor,
trying to control the stiffener dimensions. It seems that aluminum
stretches when coined, often in a rather unpredictable manner. I
eventually gave up and went to 0.125" sheet aluminum and no
stiffeners. Unfortunately, only a handful of prototypes were made and
shipped, so I have no clue as to how well (or badly) they worked in
the field.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 22 nov, 03:24, Roy Lewallen wrote:
Wimpie wrote:
. . .
There is an "however". When you make a single turn loop from flat
strip that has the same width as the length of your two-turn loop, you
will notice: *1. reduced AC resistance (because of the significantly
larger circumference of the flat strip with respect to a thin round
tube, 2. inductance will decrease (H field lines have to take a longer
path around the wide strip), 3. radiation resistance will not change
with respect to a single turn loop from wire/tube.
This results in higher efficiency and increased bandwidth. * The
overall result will be better then for your two-turn loop. I think
that is the reason why most programs are for single turn loops.

So for the transmit case, given fixed diameter of your loop, the
larger the copper surface (=length*circumference), the better the
efficiency. *Best thing to enhance conductor surface is to use very
wide flat strip (high wind load), or multiple wires (with some spacing
in between) in parallel (limited wind load).
. . .

Flat conductors aren't as attractive as they look at first glance. The
problem is the same proximity effect mentioned earlier in the posting.
Current is distributed evenly around a round conductor (assuming the
perimeter is a very small fraction of a wavelength), but not along a
flat strip. Because of proximity effect, the current is much more
concentrated near the edges than at the middle. The result is that the
resistance is considerably higher than for a wire with the same surface
area. In figuring an "equivalent diameter" of a thin flat strip in order
to get the same L and C properties, the rule is that a strip is
equivalent to a wire whose diameter is half the strip width. This means
that a strip of width w or total "circumference" 2 * w is equivalent to
a wire with a circumference of pi * w / 2 ~ 1.6 w, in so far as L and C
go. Since the same phenomenon affects the inductance and resistance,
this would also be a good working rule for estimating the relative R of
a strip or wire.

Roy Lewallen, W7EL

Hello Roy,

You are right regarding non-uniformity, losses in the flat strip are
higher then based on the uniform current distribution (because of non-
uniformity). But this does not declassify loop antennas out of strip
material.

Based on a uniform current distribution (20cm wide strip versus two-
turn loop from tube with D=2cm) one would expect heat loss reduction
of 3.2. In my posting on Art's comment a mentioned heat loss reduction
w.r.t. the 2-turn loop of factor 2.5 (to account for non-uniformity).

A strip (not near to other constructions) has effective diameter of
half the width to have same characteristic impedance (as you
mentioned). So a strip with physical circumference of 40cm (width =
20cm) has an effective circumference of 40*0.785=31.4cm. You need to
have tube with D=10cm to have same effective circumference. I agree
with you that this effective circumference is also a good starting
point for calculation of AC loss resistance.

When Dloop is no longer large with respect to Dtube, current in the
tube tends to take the shortest path, hence reducing effective
diameter (and loop area) of the loop. In case of the strip, effective
diameter (hence area) does not reduce. Radiation resistance is
proportional to A^2 (for electrically small loops), hence Dloop^4.
10% reduction on loop diameter, gives 34% reduction of radiation
resistance.

In my opinion, advantage of a strip is still significant with respect
to a tube as long as you use a strip with width 2*(tube diameter).

Best regards,

Wim
PA3DJS
www.tetech.nl
you can use PM, but please remove abc.

In article ,
Roy Lewallen wrote:

Wimpie wrote:
. . .
There is an "however". When you make a single turn loop from flat
strip that has the same width as the length of your two-turn loop, you
will notice: 1. reduced AC resistance (because of the significantly
larger circumference of the flat strip with respect to a thin round
tube, 2. inductance will decrease (H field lines have to take a longer
path around the wide strip), 3. radiation resistance will not change
with respect to a single turn loop from wire/tube.
This results in higher efficiency and increased bandwidth. The
overall result will be better then for your two-turn loop. I think
that is the reason why most programs are for single turn loops.

So for the transmit case, given fixed diameter of your loop, the
larger the copper surface (=length*circumference), the better the
efficiency. Best thing to enhance conductor surface is to use very
wide flat strip (high wind load), or multiple wires (with some spacing
in between) in parallel (limited wind load).
. . .

Flat conductors aren't as attractive as they look at first glance. The
problem is the same proximity effect mentioned earlier in the posting.
Current is distributed evenly around a round conductor (assuming the
perimeter is a very small fraction of a wavelength), but not along a
flat strip. Because of proximity effect, the current is much more
concentrated near the edges than at the middle. The result is that the
resistance is considerably higher than for a wire with the same surface
area. In figuring an "equivalent diameter" of a thin flat strip in order
to get the same L and C properties, the rule is that a strip is
equivalent to a wire whose diameter is half the strip width. This means
that a strip of width w or total "circumference" 2 * w is equivalent to
a wire with a circumference of pi * w / 2 ~ 1.6 w, in so far as L and C
go. Since the same phenomenon affects the inductance and resistance,
this would also be a good working rule for estimating the relative R of
a strip or wire.

Roy Lewallen, W7EL

does this rule also hold true for example i've opened some tuners
and linear amps, often, i see straps instead of wire going to the
larger coils and switches, even some switch box's have straps from
relays to connectors etc would wire have been 'better' and or
avoid the proximity effect??