LOOPS square vs round and eggbeater too!
JEEPMON
A square loop or a round loop?
Is a square loop or a round loop just a dipole 'bent'?
What are the pros and cons of a horizontal vs. a vertical loop?
For a loop should the TOTAL length be 1/2 or a full wavelength?
How do you feed them (and not with food or your hands either please)!?
Why do some people insist the a Square loop should be 'fed' at a corner
rather than in the middle if one 'side' of it?
How do I match 50 OHM coax to the loop?
What is the impedance of a loop and what changes it.
People talk about 'nulls' with loops but if the entire loop radiates why are
there any nulls and how do you re-shape a loop to get rid of nulls?
What would change with a loop antenna if you added more 'sides' to it until
it was a circle? IE- if the loop was 3 sided, than 4 sided (square), then 5
then 6 then 7 then 8 ect........? Would this affect the nulls or impedance?
If I make a square loop out of copper plumbing tubing does the wall
thickness or diameter of the tubing affect the antenna?
I have seen 'eggbeater' antennas. Are the dipoles whose ends are bent (like
a square or circular loop) but are not on the same plane?
If so is an eggbeater antenna directional.
All eggbeater antennas I have seen are vertical what if you 'lay' them on
their side? (don't answer they goto sleep either!)
I need more info on loop antennas but when I search I find a bunch of
'receiving loop antennas' for short wave and none for transmitting also they
are all several turns of wire around a form not just a single one I am
looking for information about.
Please help me?
I know there are LOTS of antenna software out there but are there any
specific for loops and helping me design them?
AND THANK GOD FOR NEWSGROUPS AND SPELLCHECKERS!
Dale Parfitt
Traditional horizontal VHF/UHF loops are shortened dipoles bent into a circle or
square. Because the current decreases out from the feedpoint (even when the
dipole is capacitively loaded at its ends) the resulting pattern is eggshaped-
typically by approx 3dB- whether it is a square or circle. A few years back a
manufacturer released a full wave loop for 2M- a full wave loop has a pattern
very similar to a dipole- i.e. 2 deep nulls- and a bit less gain than a dipole.
It did not last long in the market.
One halo 6M antenna from several years back radiated as much from the feedline
as it did the antenna- no balun.
Two antennas offer a nearly perfect omni patterns- big wheels and the PAR
Omniangle- a .7 wavelength triangular antenna.
Dale W4OP
'Doc
JEEPMON,
A loop antenna becomes more efficient as the area inside
the loop becomes larger; circle, square, triangle. When you
just say a 'loop', in general it's understood to mean a full
wave length. If it's a 1/2 wave length, then it's usually
stated as a '1/2 wave loop' (1/2, 1/4, etc.).
Horizontal loops are usually omnidirectional, vertical
loops are usually bidirectional (depending on height). The
'pros + cons' of polarization are like most other antennas,
radiation in no particular direction, or in some particular
direction.
The input impedance of a full wave loop depends to a
large extent on the 'shape' and height above ground. The
more area inside the loop, the lower the input impedance.
As a very broad 'rule', it's input impedance is something
on the order of about 100 ohms. The less area inside the loop
the higher the iompedance, eg: a 1/2 wave folded dipole's
input is about 300 ohms. Feedline a full wave loop at a corner
gives it a 'vertical' polarization (sort of). Feeding it
on a side makes it horizontally polarized (sort of).
There are a number of ways to feed a loop with 50 ohm
coax. Any matching system will work (gamma, delta, etc),
or using a 'matching section' of 75 ohm coax, or ladder
line and a tuner/balun will work. Just depends on your
preference as to which one to use.
Most antennas will have a 'null', depending on it's
oreintation, etc. A vertiaclly mounted loop tends to
have a radiation pattern like a 1/2 wave dipole,
bidirectional (depending on height). The easiest way of
getting rid of the 'nulls' is to lower the antenna (not
the best way, but the easiest). I'm sure if you 'played'
with it long enough, changing the shape of the loop may
affect the 'nulls' (I don't think you'd get rid of them,
but you might get more of them).
The size of the conductor making up an antenna does
have an affect on it's performance, usually making it
broader banded to a point, and a few other things. Pipe
would work just fine. You'd have to experiment with the
lenght for tuning, but that shouldn't be a problem.
Laying an 'egg beater' on it's side will surely have
some affect, but I have no idea what (you rulled out my
best answer).
You might try a search using "full wave loop" and see
what you get. There has to be some information available.
good luck with your antenna project! Getting there is
half the fun, so enjoy the trip...
'Doc
Lee Carkenord
> A square loop or a round loop?
> Is a square loop or a round loop just a dipole 'bent'?
> What are the pros and cons of a horizontal vs. a vertical loop?
> For a loop should the TOTAL length be 1/2 or a full wavelength?
Mr. Cebik, W4RNL...has a good website. I suggest going there and
reading thru his various "loop" topics....I am sure you will find some
answers.
And good luck to you.......loops are fun.
Lee Carkenord KA0FPJ