---

Do you Yahoo!?
- 50x more storage than other providers!

When I looked at the end of that cable I only saw 6 wires. Upon
taking the white covering back I see 4 twisted pairs. White and 4
colors. No shielding. All insulated. Telephone? I am sorry and
will try to be more careful in the future.

Probably Category 5 networking cable. The copper wires in it will
work fine.

Just to clear up hopefully one last question-- are you saying to

take

the insulation off of everything and just have bare wire? Or can

I

leave the insulation on the little wires and take off the outside
covering?

Take off the outside covering, and only remove insulation where you
need to twist wires together to make a longer wire, and where you
connect it to the radio.

When I looked at the end of that cable I only saw 6 wires. Upon
taking the white covering back I see 4 twisted pairs. White and 4
colors. No shielding. All insulated. Telephone? I am sorry and
will try to be more careful in the future.

Just to clear up hopefully one last question-- are you saying to take
the insulation off of everything and just have bare wire? Or can I
leave the insulation on the little wires and take off the outside
covering?



--- In loopantennas@..., "Bruce Carter" <brucec@m...>
wrote:

I have a cable that says
MPP/CMP/PCC FT6 -- -- 4/24. Six copper wires. Would that work?

Any
easy way to get the covering off?

I find that rolling the wires with the knife on a meat

cutting block spares my fingers from any chance of cuts.

It is interesting that you have this type of cable. I cannot find

a data sheet for that particular type of cable, but it is possible

that it is a shielded type - it has a braided conductor around the
copper conductors. IF that is

Questions: Can I use a piece of wood instead of cardboard or
styrofoam?

Wood is ideal. I mentioned the others because they are very easy to
find and work with. But if you have woodworking skills - so much
the better. I have several construction articles about making wood
frame loop antennas. Just remember that the tuning capacitor
mentioned in my articles is already inside your radio. You are
trying to match to it.

Is speaker wire too light?

Speaker wire is great - I don't usually mention it because it can be
expensive, and you have to rip the two wires apart to get a single
wire you can wind - or you could always just twist the two wires
together and make one conductor out of it.

I have a cable that says
MPP/CMP/PCC FT6 -- -- 4/24. Six copper wires. Would that work?

Yes, but I recommend ripping the six wires apart, twisting them
together, and making one continuous conductor. 150 feet divided by
6 - you would need 25 feet of the six conductor wire to start with.

Any
easy way to get the covering off?

In the absence of wire strippers, I would take a steak knife and cut
around the insulation in a circumcision fashion, then slide off the
insulation. I find that rolling the wires with the knife on a meat
cutting block spares my fingers from any chance of cuts.

It is interesting that you have this type of cable. I cannot find a
data sheet for that particular type of cable, but it is possible
that it is a shielded type - it has a braided conductor around the
copper conductors. IF that is the case, the braid will make just as
effective an antenna as the wire in the middle. The braid is a
woven metal - and can be easily un ravelled and then twisted to make
a nice end.

Thank you so much guys, Bruce and John. I sort of get a little of
this inductor/capacitor thing now. I am interested in one of the
commercial FM antennas mentioned as the reception on the TV next to
the radio is just slightly compromised now from that splitter. No
biggie, but I have to have an amplifier to get any TV at all. And
never had decent radio in 5 years. But you'all have my hopes up now.

On the AM antenna--- here I thought there was more than just wire
involved! I saw the words ferrite, and induction and freaked I
guess.

Questions: Can I use a piece of wood instead of cardboard or
styrofoam? Is speaker wire too light? I have a cable that says
MPP/CMP/PCC FT6 -- -- 4/24. Six copper wires. Would that work? Any
easy way to get the covering off?

And thanks so much for the ladder concerns, you really warmed my
heart on that. No one would hear the crash out here in the middle of
the big Missouri forest, for sure.
And good guess on the dimmer switches. Both of them are.

Thanks again,
Nancy

--- In loopantennas@..., "Stumm, John C" <jcstumm@s...>
wrote:

Greetings Clueless!
It depends on what you mean by super expensive. CCrane offers a

very nice AM antenna that would serve you well in your outlying area.
They go for a hundred bucks though, (unless you can find one on ebay
for less). You can place the ferrite "head' in a spot that maximizes
signal and minimizes noise. As far as using light switch cover
screws, they tend to be noise magnets, especially if you employ
dimmers. ccrane.com is the address and they offer other antennas as
well. The Justice AM antenna, (as it was formerly known), at $100, is
a lot of bang for your buck. They may offer free shipping also?

Good luck,
John

Greetings Clueless!
It depends on what you mean by super expensive. CCrane offers a very nice AM antenna that would serve you well in your outlying area. They go for a hundred bucks though, (unless you can find one on ebay for less). You can place the ferrite "head' in a spot that maximizes signal and minimizes noise. As far as using light switch cover screws, they tend to be noise magnets, especially if you employ dimmers. ccrane.com is the address and they offer other antennas as well. The Justice AM antenna, (as it was formerly known), at $100, is a lot of bang for your buck. They may offer free shipping also?
Good luck,
John

________________________________

From: Usually Clueless [mailto:usuallyclueless@...]
Sent: Tue 7/13/2004 8:45 AM
To: loopantennas@...
Subject: [loopantennas] AM Antenna- I am a totally clueless non radio granny --HELP?



First let me apologize for wasting everyone's time here but I am so
lost. And thanks for being brave enough to read this. I don't know
what any of these technical terms everyone writes of mean. Induction
is what happens before they put the dog tags on and the rest of the
terms you use are otherworldly to me.

My homely problem.
I was given a radio receiver with 4 clip inputs in the back that say
AM loop and FM loop. With nothing attached, nothing was received. I
do live in a fringe area.
Trying to help myself, I did a little research on the net yesterday
(found you'all then ) and so put a splitter on my TV cable, rigged up
a pigtail for the stereo, put the wire in one of the FM inputs, and
now receive FM stations I could never hear well in the house
before. What luck! Until lightning hits the TV antenna maybe?

Then for the AM I hooked up, into one of the AM inputs, various
lengths of TV/telephone cables, straight and loopy, but nothing. So,
reading from yesterday's net research , I skeptically ran a cable
(medium red/gray color covering, no writing on it, 4 wires I twisted
together) from one radio AM input to one of the two screws on the
room light switch cover. Lo and behold, 2 faint stations, and
another one that I could hear with static at the same volume level as
the broadcast.
But it was the station that I wanted to hear. Looks like my year of
luck, no? Then, heady with success I ran another pigtail to the
screw of a light switch cover that was on a different electrial
circuit. That did noticeably help the static so listening for half
an hour might be tolerable now.

Question: Can I easily improve on this AM a whole whole lot? Is
there an AM antenna to buy that is not super expensive? And easy to
use? I have an attic opening right above the radio I could throw
something large into, if need be. I see cheap little stereo antennas
on Ebay for $10-20. Would one of them work?
I have looked at antenna diagrams but after seeing parts I never
heard of, and with all the 'tuning' and 'ratios' I had a panic attack.

I would be ever so grateful for some advice. Sorry that I am so
ignorant and confused as I have lived 68 yrs and never heard of
a "loop" until 3 days ago.











Yahoo! Groups Links

Welcome to the group! We are all still clueless on this topic to
one degree or another. And the only stupid questions are the ones
that do not get asked.

I am the author of one of the loop antenna pages:



I have been told that my presentation is easy enough for novices,
but the page assumes some type of electronic knowledge on the part
of reader. I will try to make this simple.

First off, congratulations on your success with FM stations. It
shows real initiative on your part, and good deal of electronically
oriented intuition to go as far as you did and successfully receive
stations. As for the little indoor FM antennas - forget them. You
will receive far more stations by buying one of the FM "T-wire" type
antennas that may have even come with the radio. They are a dollar
or two, usually made of flat, clear wire that is about 3/8 of an
inch wide. You can probably find them at Walmart or Target, wrapped
up in a package hanging on the wall in the electronics accessory
department. Radio Shack or Best Buy will have them as well. Take
the wire out of the package, and you will find that it is shaped
like a "T", with connections for the screws of your stereo on the
bottom of the T. You will get the best reception if you use push
pins and install it at the ceiling on a wall that is closest to
broadside to the stations you want to receive. Please be careful on
the ladder! I get very good reception of stations up to 60 miles
away using one.

The next step up in FM antennas can be found at Radio Shack - they
have a 6 element FM antenna for around $25. I used mine to receive
stations up to 180 miles away. An outdoor antenna can be hidden in
an attic, and is certainly more trouble than the T-wire, but
sometimes that is the only way to receive stations.

Now, for AM loops - the main subject of this group. Without getting
into electronics terminology - the way the loop antennas we build
work is by taking advantage of the fact that two types of electronic
components - inductors and capacitors - both store electricity, but
do it in different ways. When you hook them together, they get
caught in a tug of war - transferring energy from one to the other -
at a specific frequency. That frequency is determined by the value
of each. The reason why your AM reception is so weak is that one of
them - the inductor (or coil of wire) is the wrong value. Your
capacitor is inside of your radio, so you have to match it. Right
now, it is not able to transfer energy back and forth at the same
rate as the stations are broadcasting, because the loop part is not
right. You may already know that an antenna made for UHF TV
stations probably would not work for VHF TV or FM, neither would an
antenna made just for FM work very well with UHF TV. It is exactly
the same principle the AM loop. You have to construct it correctly
to receive AM stations in conjunction with the capacitor inside your
radio.

Now, for a simple construction project. A lot of us have had
success with a Pizza box, but anything of that general size will
work. Styrofoam out of TV box, for example. Just something that
makes a big square or circle, and is not made of metal. It will be
near your radio, so you might want something that isn't too ugly!
14 by 14 inch square is fine. 20 by 16 inch rectangle is fine. 18
inch round is fine.

Next, you need to buy about 150 feet of wire. Home Depot and Lowe's
have packages of 50 feet or 100 feet, you will probably have to
twist shorter pieces together to make 150 feet. Copper wire is
best, it doesn't have to be thick or heavy or anything like that.
Insulated wire is best, but you may not have a wire stripper to deal
with it. It does have to conduct electricity efficiently when
twisted together. Steel or aluminum wire is not good.

Wrap all 150 feet around whatever it is you have for a frame. You
need to separate each turn of wire a little bit, so it doesn't short
against the next turn of wire.

I have purposely had you make an antenna that is a bit too "low" in
frequency - but it may work satisfactorily just as is. Each end of
the wire you wound around the box (or whatever you used) goes to a
screw on the radio.

If you aren't getting good reception, make sure the antenna is
standing up vertically and not flat (like it was on the floor). You
can also try turning it, loops are directional and this type is most
sensitive along its edge. Finally, you can try taking turns of wire
off, one at a time, until you get the best reception. My guess is
no more than 3 or 4 if you used a pizza box. If you take off too
many, you can twist it together again and add back a turn of wire.

When you get it the way it works best, use some tape to keep the
wire in place on the box.

Please let us know how it works, we are here to help you if you need
more advice!

First let me apologize for wasting everyone's time here but I am so
lost. And thanks for being brave enough to read this. I don't know
what any of these technical terms everyone writes of mean. Induction
is what happens before they put the dog tags on and the rest of the
terms you use are otherworldly to me.

My homely problem.
I was given a radio receiver with 4 clip inputs in the back that say
AM loop and FM loop. With nothing attached, nothing was received. I
do live in a fringe area.
Trying to help myself, I did a little research on the net yesterday
(found you'all then ) and so put a splitter on my TV cable, rigged up
a pigtail for the stereo, put the wire in one of the FM inputs, and
now receive FM stations I could never hear well in the house
before. What luck! Until lightning hits the TV antenna maybe?

Then for the AM I hooked up, into one of the AM inputs, various
lengths of TV/telephone cables, straight and loopy, but nothing. So,
reading from yesterday's net research , I skeptically ran a cable
(medium red/gray color covering, no writing on it, 4 wires I twisted
together) from one radio AM input to one of the two screws on the
room light switch cover. Lo and behold, 2 faint stations, and
another one that I could hear with static at the same volume level as
the broadcast.
But it was the station that I wanted to hear. Looks like my year of
luck, no? Then, heady with success I ran another pigtail to the
screw of a light switch cover that was on a different electrial
circuit. That did noticeably help the static so listening for half
an hour might be tolerable now.

Question: Can I easily improve on this AM a whole whole lot? Is
there an AM antenna to buy that is not super expensive? And easy to
use? I have an attic opening right above the radio I could throw
something large into, if need be. I see cheap little stereo antennas
on Ebay for $10-20. Would one of them work?
I have looked at antenna diagrams but after seeing parts I never
heard of, and with all the 'tuning' and 'ratios' I had a panic attack.

I would be ever so grateful for some advice. Sorry that I am so
ignorant and confused as I have lived 68 yrs and never heard of
a "loop" until 3 days ago.

Bruce,

I like the new front page. The graphs showing the difference between
single and multi-turn loops were especially welcome. I'm surprised
that there wasn't a greater difference but that may have more to do
with transmitting efficiency rather than in a receiving application.

TNX es 73,

'Bear' NH7SR

--- In loopantennas@..., "Bruce Carter" <brucec@m...>
wrote:

Good morning,
Thanks to everyone who responded to my new guy question. I appreciate it
and hope to give input to the list as time goes on. Have a great weekend.

73
Steve N4TKP

Chris,

Ummm... stronger stations with the plates disengaged? Well that would
work to attenuate their signals. For the weaker stations you should
find a very pronounced peak in strength as you tune across them with
a rapid decrease on both sides.

Glad it's working well for you and looking forward to the photos.

73,

'Bear' NH7SR

--- In loopantennas@..., lockmanslammin@a... wrote:

well, its done, and it works quite nicely. Thank you for the

responce. The

cap I used has two seperate setts of plates, so I hooked up a small

toggle

switch, so i can run both sets or just one. I though that was kinda

cool, and it

does help sometimes to have the choice. Also I noticed that

stronger stations

need the cap plates to be competely un engaged, and that the weaker

stations

are usually somewhere in the middle. Interesting stuff, I think I

will enjoy

playiong with this new toy...lol. Thanx again,

Chris

开云体育

That is a very nice looking loop.

--- lockmanslammin@... wrote:

thanx for the reply,
while I was waiting for the reply I ended up making
one, maybe you could tell
me if I'm on the right path. It is 19" X 19" square
with 18 turns on it, both
begginning and ending on the same leg. I used
stranded 20 guage hook up wire
from the Rat Shack, wich didn't come in a long
enough spool, so I very
carefully soldered the two together end to end and
shrink wrapped it, for a very nice
splice. Then I ran a coupling turn, that is very
very slightly smaller
diameter than the main windings, like maybe an 1/8th
inch smaller or so. I cut small
grooves in the leg ends so the wires would be very
symerically spaced, and
the 18 winds take up 4 1/4"s on the leg ends. I
found a used variable resistor
at a local electronics shop. I made a gear reduction
box for it and attched a
knob to the smaller gear, I'm happy with the
results, it works very smoothly.
The point I'm at right now is I still have to attach
the cap to the frame and
wire it. Heres what I'm not sure on. I wire one
sidfe of the main winding to
the fixed plates and the other side of the main
winding to the moving plates via
the soldering tabs, right? also how do I hook it to
the reciever?

The primary loop need not connect to the receiver at
all. That is one of the nice things about loops, they
are inherently "balanced" antennas and can completely
float.

Do I just

hook one side of the single coupling wind to the
antenna connection and the
other to the ground? Does the coupling wind have to
be hooked to the variable cap
at all? Does it have to be twisted together? Do I
need some sort of a diode
atached to the coupling wind in series for the
reciever to recognise the
signal?

The output loop generally floats. That is, it isn't
connected to the primary loop at all. If the receiver
has an unbalanced input, one side of the output
winding is grounded and the other hot. If it is a
balanced input, it is both leads into the balanced
input. You don't need a diode, the detector stage in
your radio will do that for you. I have a radio that
had no external antenna input so I made a balanced one
by winding 10 turns of wire around the existing
ferrite loop.

I will include a pic of the cap with the gear drive
I made and the loop I
made so you can see what I'm talking about.
Thanx again,
chris

__________________________________
Do you Yahoo!?
Yahoo! Mail Address AutoComplete - You start. We finish.

--- Michael Hebert <qrpbear@...> wrote:

With the kind of bandwidth you are getting on 40m I would say the
loop's Q is seriously degraded. You should only have about 15-20 KHz
between 1.5:1 points. KI6GD's loop calculator predicts an efficiency
of about 28% for a loop made of 1/4" copper pipe. I would say that
your loop's efficiency is well below that figure especially since the
BuddiPole beat it out. The BuddiPole is probably only about 10%
efficient on 40m.

I agree... The loop is supposed to be a tuned circuit. With the unusually broad
bandwidth, I think it has losses somewhere.

Try a CW keydown test for a couple of minutes then feel the tubing in
the area around the gap. If it feels warm you have some nasty
dielectric losses occuring. What kind of insulation does the wire use
and what is it's voltage rating? If it's the common 600 Volt wire the
insulation is probably PVC which is OK so long as you use the white
wire rather than the black or green wire. PTFE insulated wire would
be preferable from a loss standpoint. The ends of the wire should be
smoothed off and well insulated. Any sharp points there could arc or
develop corona discharges.

I will try that key down test some time. The wire is #10 stranded THHN with a
white insulating jacket rated for 600V. I wonder if I would have done better to
use solid instead of stranded. I tried to use electric tape over the ends of
the wire to reduce short circuit/corona on the ends of the capacitor-wire.

I still think your "wire inside" tuning idea is a good one but you
definitely should be getting better results. It may be necessary to
bridge the gap with a fixed capacitor and use the wire for fine
tuning.

I may try using a piece of coax for a capacitor and see how that performs. I do
not have access to high voltage capacitors (fixed or variable).

Since I'm limited on power (Elecraft K2 @ 15W), the loop would be better used
on 20m where it should be more efficient for its size. I was lucky to be heard
last night using 15W SSB into the buddipole at its height. I'm normally a CW
op, but my mini-paddles lost one of the leads (for the 2nd time).

FWIW - the buddipole received everything about 10dB stronger than the loop. The
long wire wasn't any stronger than the loop (although I can't tell if it was
weaker than the loop). There are overhead utility lines that pass over the last
30 feet of the wire. Most operators were complaining about all of the
noise/static crashes they were hearing last night, and I was hearing most
everyone clearly. I don't know whether to attribute this to the loop antenna,
antenna height, propagation, K2 receiver, or a combination of these.

73,
Daniel / AA0NI

开云体育

Daniel,

With the kind of bandwidth you are getting on 40m I would say the
loop's Q is seriously degraded. You should only have about 15-20 KHz
between 1.5:1 points. KI6GD's loop calculator predicts an efficiency
of about 28% for a loop made of 1/4" copper pipe. I would say that
your loop's efficiency is well below that figure especially since the
BuddiPole beat it out. The BuddiPole is probably only about 10%
efficient on 40m.

Try a CW keydown test for a couple of minutes then feel the tubing in
the area around the gap. If it feels warm you have some nasty
dielectric losses occuring. What kind of insulation does the wire use
and what is it's voltage rating? If it's the common 600 Volt wire the
insulation is probably PVC which is OK so long as you use the white
wire rather than the black or green wire. PTFE insulated wire would
be preferable from a loss standpoint. The ends of the wire should be
smoothed off and well insulated. Any sharp points there could arc or
develop corona discharges.

I still think your "wire inside" tuning idea is a good one but you
definitely should be getting better results. It may be necessary to
bridge the gap with a fixed capacitor and use the wire for fine
tuning.

73,

'Bear' NH7SR

--- In loopantennas@..., aa0ni@y... wrote:

I was able to get the antenna to tune up on 40m, but had to switch
from magnetic coupling to a direct matching system (shield of coax

at

center point of loop tubing, and moving end of coax along the

length

of the loop tubing until properly matched). Before I did this, the
best I could get on 40m was 2:1. Now I get 1:1.

I get a pretty broadband response on 40m (160kHz 2:1, 110kHz

1.5:1).

I'm concerned that maybe I'm doing something wrong. I don't have

the

sharp response expected from a Hi-Q circuit on 40m. Is it possible,
like was mentioned, that the distributed capacitance is making the
antenna broader in frequency response? Since it is broader in
frequency response - does that hint of great inefficiency? I don't
have a field strength meter to run a comparison.

Unfortunately, it does not seem to be very efficient on 40m. I was
running 10-15W SSB on 40m, and my buddipole (at 9-10 ft) did better
than both the 20' loop and my 100' wire (both at 5'). This was with

a

station near Dallas (I'm in OKC) near local sunset. He was running
500W to an inverted V up 1/4 wave (35 feet). The buddipole was just
above the noise level. Both the loop and longwire were unreadable.

Hoping there's something I can do to remedy this loop (other than
putting it back on 20m).

- Daniel

Chris,

Sounds like you made a very fine loop, indeed! The only thing I would
have done differently is to make the coupling loop about 1.5" to 2"
in from the main loop winding. That helps improve the Q (Quality
factor) and sharpens up the tuning. It wouldn't make much difference
as far as signal strength is concerned.

As far as connections go... Yes wire one end of the loop winding to
the solder tabs on the variable capacitor and the other end to the
frame. It doesn't matter which end goes where. One end of the
coupling loop goes to antenna input and the other to ground on your
receiver. Twisting the wires between the loop and receiver at about 2
twists to the inch will make that portion act as a transmission line
rather than a short antenna. This will improve the loop's ability to
null interference when you rotate it.

You don't need a diode between the loop and the receiver... just hook
it up, tune it up and enjoy!!

73,

'Bear' NH7SR

I was able to get the antenna to tune up on 40m, but had to switch
from magnetic coupling to a direct matching system (shield of coax at
center point of loop tubing, and moving end of coax along the length
of the loop tubing until properly matched). Before I did this, the
best I could get on 40m was 2:1. Now I get 1:1.

I get a pretty broadband response on 40m (160kHz 2:1, 110kHz 1.5:1).
I'm concerned that maybe I'm doing something wrong. I don't have the
sharp response expected from a Hi-Q circuit on 40m. Is it possible,
like was mentioned, that the distributed capacitance is making the
antenna broader in frequency response? Since it is broader in
frequency response - does that hint of great inefficiency? I don't
have a field strength meter to run a comparison.

Unfortunately, it does not seem to be very efficient on 40m. I was
running 10-15W SSB on 40m, and my buddipole (at 9-10 ft) did better
than both the 20' loop and my 100' wire (both at 5'). This was with a
station near Dallas (I'm in OKC) near local sunset. He was running
500W to an inverted V up 1/4 wave (35 feet). The buddipole was just
above the noise level. Both the loop and longwire were unreadable.

Hoping there's something I can do to remedy this loop (other than
putting it back on 20m).

- Daniel

Daniel,

Very interesting post! I like your idea for the tuning capacitor. I
thought about a somewhat similar approach using a larger diameter
copper pipe sliding back and forth over the gap in the loop but never
got around to building it. Your method would be considerably less
complicated.

I ran a quickie calculation using KI6GD's loop calculator which shows
an efficiency of 79.9% and a bandwidth of 75.3 KHz. Since you are
getting 300 KHz the capacitor is probably lowering the loop Q due to
linear loading. Efficiency would be somewhat less but probably not
any detectable difference in signal strength when you're transmitting.
KI6GD's calculator also predicts 3.2 kV across the capacitor assuming
a lumped capacitance at the gap. It will probably be considerably
less than this with distributed capacitance.

I also found that squashing the coupling loop improved matching to
the main loop. Positioning it dead center or offset to either side
did not make any significant difference on my 10' circumference loop.

At low mounting heights the MagLoop does exhibit better low angle
performance than a dipole at the same height. The pattern of a
MagLoop mounted 1 loop diameter above ground is primarily straight up
but it does have better low angle figures than a dipole when modeled
in EZNEC. Raising the loop higher improves the low angle figures even
more and the pattern begins to change as you go higher than 1/4
wavelength above ground. The high angle pattern begins to flatten out
and the low angle response starts moving towards even lower angles.
Above 1/2 wavelength mounting height lobes begin to develop in the
vertical radiation angle patterns.

Any performance comparison with a dipole has to be tempered by the
fact that a dipole exhibits about 2.38 dB gain over isotropic while a
MagLoop shows a loss compared to isotropic with the loss being
relative to the loop size. The characteristics of the ground
surrounding the antennas at a distance of up to 1/4 mile also needs
to be taken into consideration since it directly affects the take-off
angle of the antenna.

I have not found rotating my loop to offer any benefit. The azimuthal
pattern of a MagLoop at vertical angles above 30 degrees is
essentially omnidirectional. Mine is situated in a North/South plane
and seems to work just as well for all directions.

Thanks again for such an informative post and the great idea!

73,

'Bear' NH7SR

--- In loopantennas@..., aa0ni@y... wrote:

I just joined the list because I've been wanting to build a compact
transmitting loop for many months now, and I was met with good
success late last night (around 12-1 AM, while I was waiting for

the

caffeine to settle down in my system... but that's another story).

A couple goals I had were simplicity in design (fixed tuning, basic
monoband/QRP use, no expensive tuning capacitor), simple assembly

(no

pipe soldering), readily available materials (Lowe's), and high
efficiency (circumference >1/10 wavelength, very low resistances).

I

want the design to be reproduceable so that a ham who didn't have
access to an antenna analyzer could build one of these and know

that

it would work with minimal amount of fuss.

I used 20 ft of 1/4" flexible copper tubing (less than $10) taped

to

a 1/2" PVC pipe cross. The advantage of the flexible copper tubing

is

that there are no joints to solder, minimizing any resistive

losses.

The disadvantage of 1/4" tubing is that you need to use alot of it

to

make up for its small diameter.

For tuning, I used a 2 ft piece of #12 THHN solid wire. This wire

was

placed in both open ends of the pipe, and then moved back and forth
until proper tuning was achieved. This type of tuning is similar in
action to a butterfly capacitor (no resistive losses from a stator)
or a trombone capacitor, except that it is using the antenna tubing
itself as part of the plates, and the wire is coupling the two

sides

together just like the butterfly stator (very low resistance -
improving efficiency).

The #12 THHN was free, but I'm going to acquire some #10 THHN which
is the largest size I've found that will fit in the 1/4" tubing. By
using #10 THHN, there will be less problems with wire not being
equidistant from the inside of the tubing. The #12 can 'float'

around

the inside of the tubing. Using #10 should give consistent results.
It will also increase the capacitance as the gap between the
innerwall of the tubing and the #10 wire decreases.

The antenna is fed with 20 ft of RG-8x (8-mini). A four foot loop

was

construced on the end with the center conductor soldered to the
shield/braid of the coax four feet back from the end of the coax.

I realize that 20' is not really 'compact' for 20m. For me, this

was

more a proof of concept. I intend on using the 20' for 30m or 40m.

I

will probably try to use 10' for 20m.

The results? 2:1 SWR bandwidth is about 300 kHz on 20m (but tuning
was tricky). The SWR was measured as it was leaning up against a
wooden fence in the backyard, and the bottom of the loop was less
than 2 feet off the ground. The coupling loop is very flat against
the copper tubing. Instead of being a nice circle, it is a very
squashed oval (which brought the SWR down from 2:1 when circular to
1.3:1 when a flat oval). Before I started mounting the copper

tubing

to the PVC frame, I should have straightened the copper tubing out
and marked off the half point and quarter points so I could be sure

I

was mounting the coupling loop at the center point. This would have
removed the guess work from mounting the antenna to the PVC support.

Because the tuning is so touchy, my next goal is to mark the wire
where it now sits in the tubing. I'm guessing that I am using way

too

much wire for the capacitor on 20m. I want to try to find a wire
length, that when centered between the two openings, will tune the
loop to near 14.000. Then, as the wire is slid to either side, the
capacitance decreases (I'm assuming), and the antenna's resonant
frequency will go up. If I shortened the 20m capacitor wire down to
it's smallest effective length for the low end of the band, any

small

adjustment should hopefully result in a small increase (only) in
resonant frequency. It might even make it possible to mark the wire
to precisely tune the antenna - e.g. moving the wire 1" from center
moves resonance up ### kHz.

I think that if a proven design can be established where a certain
known length of #10 wire combined with a certain length of 1/4"
tubing will allow a user to operate on a particular band - more
operators will be using loops in antenna restricted environments.

Thanks for the bandwidth, and any comments you have about this

design.

- Daniel / AA0NI
Oklahoma City

p.s. I'd be curious to know how close to the ground you use your
loop, and does it act more like an NVIS antenna like a dipole

would,

or do you get out better towards the horizon then the dipole at the
same height. There seems to be quite a debate about the loops

ability

to outperform a dipole antenna at a low height.