We're up to 55 members! And lots of activity.

Remember, if you have not posted yet, all new members are moderated.
So don't be alarmed if your first message takes a few hours or a day
to appear. I get on fairly often to check, subject to Real Life(tm).

Once you've posted, I'll set you unmoderated. Just my way of quietly
blocking spammers.

Steve Greenfield,
moderator of the new loopantennas

--- In loopantennas@..., Barry Savage <sofistic@s...> wrote:

Hello All:
For some time now, I have been wondering about the electromagnetic

properties of common materials, and find these things rather hard to
discover. The few times I have asked about them on different
electronics-oriented groups, most people have dismissed them as not
workable. I don't want to get too off-topic, but I hope some of you
can point me in a productive direction. I also wanted to ask some
rather nieve questions that I hope someone can either answer or point
me in the right direction. So, here goes.

QUESTIONS:
1. Would it be possible to make a VLF loop-stick out of rebar?

First thing I can think of is that the remnance of rebar would be a
problem, but nowhere have I been able to find the magnetic properties
of such a readily available and cheap material. What about its
permeability, its coercivity? What does its B/H curve look like?

The problem is that it is conductive, and so you'd have I2R losses in
the induced current within the rebar. That is why cores are made out
of nonconductive ferrite, and transformer cores are made of thin
sheets of iron insulated from each other by layers of laquer.

If you look up old projects like building your own Model T spark coil,
or building one of those ring launchers with a bundle of welding rods,
note that they all require you to paint the rods to insulate them from
each other.

So- how about welding rods? Get a pound of the smallest diameter you
can find. Carefully paint them, then bundle them when dry.

2. If a "square" coil is considered optimal, why is an air-core

loop antenna so far out of square? I know aperture is an issue here,
but what are the trade-offs in terms of Q and lack of symmetry between
diameter and coil-depth?

I thought a round coil was optimal. It's just easier to build a square
coil. For the same circumference, a round coil has a larger area
enclosed than any other shape.

BTW, some ham in the state of Washington (don't have the link

offhand, but I can look it up if anyone is interested) has a
spreadsheet called "professor Coyle" that is very good for modeling
coils (both solenoid and spiderweb). I have modified it to include
wire resistance tables and a few other bells and whistles.

Where? Let us see it!

HARE BRAINED IDEAS:
1. What if you built a "steerable null" antenna using two identical

loop antennas at the end of a rotatable beam, and, in turn (heh) each
of the loops were also rotatable? Something Bear said awhile back
triggered this idea off, and I remembered experimenting with a crystal
set from Gollum's Crystal Radio site that used two spider-web coils,
one for the antenna and one for the crystal detector. The coils were
coupled (face to face) at a distance of about 6-inches, but I could
get very responsive results even at a distance of 12-inches apart, so
I played around with rotating one with respect to another and found
the nulling very sharp. I haven't done any measurement of this
arrangement, so this is only an intuitive observation.

BTW, I also built a "box" loop using a wooden "in-basket" I got at a

Michaels craft store, and used the ears of the in-box to mount it on a
base (also from Michaels) so it became an altazimuth loop. It works
very well with my little Radio Shack DX-370 at a distance of about
6-inches. The bottom of the in-box is used as the face of the loop,
the edge of the box is where the coil is wound, and a little poly
variable cap is mounted at the center of the "bottom" of the in-box.

2. Is a helical considered a loop? What if you built a large

helical antenna and treated it as if it were a loop antenna? I mean,
a helical is just a streached-out loop, isn't it? The only difference
I can see is that the distributed capacitance drops and so does the
inter-winding inductance. Humm, what am I missing here?

I seem to recall that someone (QRPBear?) tested this idea with loops
of the same diameter and turns. And found that for an air core, it
made little difference.

The problem is that the further each turn is from the next, the less
they are coupled inductively to each other. So a loop spread out into
a helix may lose efficiency. Hopefully someone with more theory and
experience under their belt can tell us.

Some spread of the turns will reduce interwinding capacitance, but you
quickly reach a point of diminishing returns.

Of course if it is on a ferrite core, that is different. How exactly I
can't say. :'/

3. A few times on this list someone has mentioned mobius-strip

loops; what is the theory behind them and how well do they work? What
are their properties in a vertical and horizontal plane of
orientation? (oops, that was a question, not a HBI)

Mobius strip loops? Hmm... I'm curious too. I can see an easy way to
"wind" one. Use the method of using a ribbon cable- only give it one
turn before you offset and solder. No, that won't work, I just gave it
a mental try and you end up with a one turn loop with a bunch of two
turn shorted turns and a one turn shorted turn. Does the same if you
don't offset. So what is a mobius loop antenna?

Steve Greenfield

Bear,

Guess my math-speak was a bit more obscure than the duck-speak in my
direct-conversion receiver. In less mathy technese:

1. While it looks like a pi network, it operates more like an L
matching network. That's because it uses the loop's inductance
partially compensated by the distal capacitor as the inductive leg.

2. No terminating resistor is needed. It's actually a disadvantage
to use one.

3. The impedance of free space only plays in the physics of finding
the loop impedance from first principles—something I've never seen
done outside of university exams. An impedance bridge will do the
trick.

4. The main advantage over the Colpitts-like matching network using
the same parts values is that both capacitors have one side returned
to common. That does not help much in the broadcast band where the
proximal capacitor has a very large value. Above 15 or 20 MHz real
variable capacitors can be used. With traditional variable caps,
being at common becomes a decided advantage for easy construction
and somewhat reduced hand capacitance.

Walking the southern 3 km of the Bothell-Everett highway yesterday
(I was thinking about the next experiment with my 1-evening direct
conversion receiver and got on the wrong bus), I noticed a few
salmon berries looking ripe. The Himalayan blackberries are in
flower, so have a couple weeks before the berries are ready to
harvest. With this year's fashions the lady bears (at least around
here) have blue tummies. So unless you're going to claw your way
into big-leaf maple sap, you might as well work on loops for the
next couple weeks. By the way I arrived in Bothell just in time to
see the correct bus disgorge a passanger who'd been waiting next to
me where I'd gotten on the wrong bus. The way some buses zig-zag
through the industrial parks, walking can be faster.

Regards,

Steven

--- In loopantennas@..., "qrpbear" <qrpbear@y...> wrote:

Steve,

Ahh... thanks for that. I'm still puzzling over the math but

perhaps

they point to a possibility of success.

For those who may not be aware of the "Street Sweepings Loop" it

is

based on the idea of feeding the loop directly from 50 ohm coax

using

the loop inductance itself as part of a Pi-Network. The most
important remaining questions are... what would be the output
impedance of the Pi-net? 377 Ohms (the impedance of free space) or
some other value? Would a resistive output termination be

required?

All this preliminary to building such an animal of course. The

real

answer would be to build it and compare it against a conventional
loop of the same size but Summer is coming on and 'Bear' is more
concerned with eating berries and catching salmon to fatten up on

for

the coming Winter's sleep.... and mebbe finding Lady Bears, too

<G>.

73,

'Bear' NH7SR (Yo! Shoggoth!! Fetch me a beer!!! No... not St.

Pauli

Girl you dumb beast!!!!)

--- In loopantennas@..., "Steven S. Coles"
<steven_coles@y...> wrote:

Bear,

I tried to answer you on the GCC Loop Group. For some reason

the

post didn't appear. So:

Bear,

My shoggoth upchucked allowing me to provide the following

example:

An impedance analyzer gives an impedance of 3 + j215 ohms at 1.6

MHz

for a certain Pioneer AM loop. Let's make the proximal

capacitor

(Cp) 7900 pF and the distal capacitor (Cd) 490 pF. That gives
capacitive reactances –j12.6 ohms and –j203 ohms respectively at

1.6

MHz.

The loop in series with Cd gives

3 + j215 – j203 = 3 + j12

Using the parallel impedance formula gives

(0 – j12.6)(3 + j12)/[ (0 – j12.6)+(3 + j12)] = 50.9 – j2.4 ohms

That's not too bad for the shoggoth and me making some wild

guesses.

Cp could be a 5100 pF cap with a dip switch to add 200, 400,

800,

1600, and 3300 pF in parallel. Cd could be a 360 pF variable

with

200 pF in parallel.

Actually the shoggoth used



and transformed the negative inductor in the upper right network
into a capacitor.

Regards,

Steven

开云体育

Hello All:
I noticed that I wasn't getting any email from the various groups I
belong to, and checked Yahoo groups and each of then said my mail
was bouncing, so I went through their reactivation process and when
I went back to the Yahoo groups, there was no warning message. Yet,
I have not received any messages in the last hour or so. Could
anyone send a "testing" message to the group so I can see if my
reactivation worked?
Thanks,
Barry

Steve,

Ahh... thanks for that. I'm still puzzling over the math but perhaps
they point to a possibility of success.

For those who may not be aware of the "Street Sweepings Loop" it is
based on the idea of feeding the loop directly from 50 ohm coax using
the loop inductance itself as part of a Pi-Network. The most
important remaining questions are... what would be the output
impedance of the Pi-net? 377 Ohms (the impedance of free space) or
some other value? Would a resistive output termination be required?
All this preliminary to building such an animal of course. The real
answer would be to build it and compare it against a conventional
loop of the same size but Summer is coming on and 'Bear' is more
concerned with eating berries and catching salmon to fatten up on for
the coming Winter's sleep.... and mebbe finding Lady Bears, too <G>.

73,

'Bear' NH7SR (Yo! Shoggoth!! Fetch me a beer!!! No... not St. Pauli
Girl you dumb beast!!!!)

--- In loopantennas@..., "Steven S. Coles"
<steven_coles@y...> wrote:

Bear,

I tried to answer you on the GCC Loop Group. For some reason the
post didn't appear. So:

Bear,

My shoggoth upchucked allowing me to provide the following example:

An impedance analyzer gives an impedance of 3 + j215 ohms at 1.6

MHz

for a certain Pioneer AM loop. Let's make the proximal capacitor
(Cp) 7900 pF and the distal capacitor (Cd) 490 pF. That gives
capacitive reactances –j12.6 ohms and –j203 ohms respectively at

1.6

MHz.

The loop in series with Cd gives

3 + j215 – j203 = 3 + j12

Using the parallel impedance formula gives

(0 – j12.6)(3 + j12)/[ (0 – j12.6)+(3 + j12)] = 50.9 – j2.4 ohms

That's not too bad for the shoggoth and me making some wild guesses.

Cp could be a 5100 pF cap with a dip switch to add 200, 400, 800,
1600, and 3300 pF in parallel. Cd could be a 360 pF variable with
200 pF in parallel.

Actually the shoggoth used



and transformed the negative inductor in the upper right network
into a capacitor.

Regards,

Steven

Bear,

I tried to answer you on the GCC Loop Group. For some reason the
post didn't appear. So:

Bear,

My shoggoth upchucked allowing me to provide the following example:

An impedance analyzer gives an impedance of 3 + j215 ohms at 1.6 MHz
for a certain Pioneer AM loop. Let's make the proximal capacitor
(Cp) 7900 pF and the distal capacitor (Cd) 490 pF. That gives
capacitive reactances –j12.6 ohms and –j203 ohms respectively at 1.6
MHz.

The loop in series with Cd gives

3 + j215 – j203 = 3 + j12

Using the parallel impedance formula gives

(0 – j12.6)(3 + j12)/[ (0 – j12.6)+(3 + j12)] = 50.9 – j2.4 ohms

That's not too bad for the shoggoth and me making some wild guesses.

Cp could be a 5100 pF cap with a dip switch to add 200, 400, 800,
1600, and 3300 pF in parallel. Cd could be a 360 pF variable with
200 pF in parallel.

Actually the shoggoth used



and transformed the negative inductor in the upper right network
into a capacitor.

Regards,

Steven

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the loopantennas
group.

File : /SpiderWeaveCoils.txt
Uploaded by : alienrelics <alienrelics@...>
Description : The Basket Weave (Spider Weave) Loop Antenna Coils by RHF. With links for other parts necessary for loop ant. and crystal radio construction.

You can access this file at the URL



To learn more about file sharing for your group, please visit



Regards,

alienrelics <alienrelics@...>

Now available at:



Then click on the "design calculator utilities", and the loop
antenna calculator is at the bottom. The choice for "wire" is the
one you want. Remember this is for wire with no spacing between
turns, I will post a more general version on my site later ----

Ah, shucks, Scott! ('Bear' sheepishly grins and scuffs his foot)
Thanks!

Sounds like you've got a pretty high Q loop. I have noticed a small
degree of sideband cutting on mine at the low end of the band. The
polyvaricon cap I'm using is probably cutting down on the overall
circuit Q.

Not surprised that you got better directionality at ground level.
From about 3 MHz on down rf seems to like "falling down" and
traveling along the ground. Same thing happens with acoustic waves.
The lower the frequency, the more they hug the ground.

73,

'Bear' NH7SR

--- In loopantennas@..., "Scott Savage KC7WDG"
<kc7wdg@c...> wrote:

well tried an experiment tonight took the yaesu frg-7700 and look

outside and the pizza box loop and from what I see the loop is more
directional closer to ground and seems to work better on some
stations. Also the tuning cap needs to be very finely tweaked to peak
the station its amazing how just adjusting it can change the sound of
the audio and or remove adjacent interference. also the loops works
just about as well as my big dipole only quieter most of the time the
bonus is the size of it the loop is much much smaller and works just
as well if not better on some station because of its directionality.
I am very impressed with this MacGyver antenna or MPBL for MacGyver
Pizza Box Loop hehe. I also took and used some hot glue to secure the
turns in 4 spots on each side also on the corners I may take some
pics later for you guys its ugly but works great. Also thanks to
everyone who suggested ideas and what not and a big thanks to bear
for the description.

Scott
KC7WDG


----- Original Message -----
From: Bruce Carter
To: loopantennas@...
Sent: Wednesday, June 09, 2004 12:27 PM
Subject: [loopantennas] Re: Pizza box loop


Or better yet get a clean one from the pizza restaurant so it
doesn't STINK or attract ants.


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Service.

Gilles,

HF horizontal loops are usually fairly large antennas. Typically cut
to 1005/f(MHz) for circumference in feet. They are often fed with
open wire transmission line using balanced antenna tuners. This makes
them capable of operation over a range of up to 3 octaves. Their
radiation pattern depends on whether they are operating on their
fundamental frequency, a harmonic or somewhere in between. Take off
angle (and best reception angle) is dependent upon height above
ground. They do have a reputation for being relatively low noise. I
say relatively because when they are mounted at a height less than
1/4 wavelength above ground they have a predominantly "straight up"
radiation pattern which makes them very efficient at picking up
atmospheric noise.

Hope this helps you.

73,

'Bear' NH7SR

开云体育

Hello !
Question in the title...
Can anybody give me some info about these antenas ?
73's
Gilles FM5AD

Following up on a post in the VLF group this morning I visited
Renato's VLF site at...

<>

where he posted details of a new antenna he is using for VLF/ELF
reception.

<>

Although the antenna is designed for VLF/ELF it is quite possible
that the same approach will work well for LF/MW and maybe even HF.

As we say here in Hawaii... Try look!

73,

'Bear' NH7SR

Here is another link to a site dealing with compact antennas
including the coffee can antenna, cone disk, bicone and eh antennas.
There are a number of useful Javascript calculators here as well.

<>

Check out the "What Can Small Antennas Do?" and "Per request - Pages
from old Web Site" links on this site.

The emphasis here is on ham radio and antennas that can be used for
transmitting as well as receiving. The instructions for tuning with
an impedance bridge can probably be ignored if the antenna is only to
be used for receiving. Tuning "by ear" will probably work just as
well.

Much of the criticism regarding compact antennas such as these stems
from the fact that they exhibit a loss compared to a full-size dipole
or vertical. That is true... so do MagLoops. OTOH, they also have a
reputation for lower noise in receiving applications.

73,

'Bear' NH7SR (On the prowl for more goodies)

Gents,

Here's the link to a compact antenna that I think deserves more in
the way of exploration and exploitation.

<>

There's a bunch of other stuff in the Antennex site archives but you
have to be a member to access it. Wish I could port some of it over
here. Hmmm... maybe some non-infringing synopses as I have the time.

This is the kind of thing I think would be an appropriate topic for
this group in addition to our loopy stuff.

73,

'Bear' NH7SR

Steve,

DDRR stands for Directional Discontinuity Ring Radiator. I thought
about building one for 30 meters (and still may) but rejected it at
the time since horizontal space is more of a premium item for me than
vertical space. They have basically the same physical requirements as
MagLoops. Fat conductors, low loss connections, high voltage
capacitors if you're gonna transmit through them. Since they are more
akin to a 1/4 wavelength transmission lines they are probably not as
size tolerant as MagLoops. Haven't tried it, though, so can't really
say.

I'm in favor of discussing just about any kind of compact antenna
here. There's lots of controversy over whether EH, CFA and Capacitive
Disc Antennas work or not. Most of that has to do with inventor's
claims that seem to contradict Maxwell's equations. I don't think
that is very important. Some of the designs look like they may be
very viable solutions for SWLs or folks who are limited to using
indoor antennas.

73,

'Bear' NH7SR

--- In loopantennas@..., "Steve" <alienrelics@y...> wrote:

--- In loopantennas@..., "Brian Wesley Rich"
<science@w...> wrote:

Man, where do you find the time? I mean, HAM, propmaking,

electronics,

weird antennas, mad scientisting, moderating...

I need a tutorial from you!

My brain won't stop buzzing. It's hard to wind down and sleep at
night. When I was young and my body could take it, I might stay up

for

a couple of days or 3 days (rarely!) in a row. If you only knew how
many projects I have going... I used to read Sci Fi and science
constantly, now it's datasheets and technical lit.

I'm not a Ham, though. Never learned morse code.

Way above AM BCB, but is anyone here making DDRR antennas? Those
horizontal loop, omnidirectional antennas? Direct driven ring

radiator?

Found a site for one that does not require a ground plane. It is to
the DDRR above what a vertical 1/2 wave is to a 1/4 whip with

ground.

How about microwave patch antennas? How do you feel about allowing

the

related topics of radio direction finding and low profile antennas

as

on topic subjects?

Steve

--- In loopantennas@..., "Brian Wesley Rich"
<science@w...> wrote:

Just received the invitation to join this list. Pleasure to be here;
thankyouverymuch.

Welcome!

I found a free online book on antennas, still being written. From
Rutger's University, called Electromagnetic Waves and Antennas.



Sad to say, I didn't take enough math so much of it is beyond me.

See Chapter 15 for Loop Antennas.

Steve