greetings...

I have been a ham since the mid 60's and the main antenna of choice appears
to be dipole... However, over the past few months, or so, I have been
reading more and more about this loop antenna.....

I am reasonable sure I can get more information about it so I won't bore you
with how to build one, etc, .. my question is more of why or how... Why has
this antenna become so popular over the past little while and how did it get
this popularity....What charateristics, besides seemingly not needing as
much geography to need to put up, does this antenna have that make is so
appealing?

I might consider it...for 80 or 40...

Larry ve3fxq

On Sat, 10 Sep 2005 08:46:24 -0400, "larry" wrote:

greetings...

I have been a ham since the mid 60's and the main antenna of choice appears
to be dipole... However, over the past few months, or so, I have been
reading more and more about this loop antenna.....

I am reasonable sure I can get more information about it so I won't bore you
with how to build one, etc, .. my question is more of why or how... Why has
this antenna become so popular over the past little while and how did it get
this popularity....What charateristics, besides seemingly not needing as
much geography to need to put up, does this antenna have that make is so
appealing?

I might consider it...for 80 or 40...

Larry ve3fxq



Depending upon the size of the loop in wavelengths and depending upon
where in the geometry it is fed and depending upon its height, it
might very well be a good cloud warmer - in which case it would
probably give excellent performance in the immediate area (as opposed
to DX).

People that I QSO with on 75 seem to do very, very well with loop
antennas in the evening over a range of up to 500 - 700 mi.

Hi Larry

You are talking about a shielded magloop rather than a full wave length
single quad loop...

They exhibit reasonable performance for their size and are very quiet.
ie the signal to noise is often better on the magloop than a larger
antenna. I have seen claims that the signal strength is maybe 2 S points
lower but the noise is 5 S points lower.

I have heard of configurations where a dipole is used for TX and a
magloop for RX.

The at antenna tuning makes for less chance of a strong nearby signal
desensitizing your RX. The downside of that is that you have to have
some method of doing this remote tuning. Bandwidths in the order of
20-30khz on 80m are not uncommon.

They can be built for 2:1 or 3:1 frequency coverage range. I have no
idea how the performance changes at the far end.

I actually havent built one weak grin

Hope this helps.

Cheers Bob W5/VK2YQA

larry wrote:
this popularity....What charateristics, besides seemingly not needing as
much geography to need to put up, does this antenna have that make is so
appealing?

larry wrote:
I might consider it...for 80 or 40...

How long is the loop in wavelengths?
--
73, Cecil http://www.qsl.net/w5dxp

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How long is the loop in wavelengths?
--
============================

.. . . . . and is it in the horizontal of vertical plane?

HI Cecil and the others...
How long ....
This is one of the things I would have to research if I was interested on
one...
In my imagination.. I have been thinking of these loop antennas as being
sort of a very large coil of wire as the input tuned circuit of the first rf
amplifier...
As the coil gets larger, in diameter, you need fewer turns.... So, by
extension, if you had a large diameter tuned circuit, let say 10 feet, you
would need very few turns... Unfortunately, .as well any tuned circuit, you
need a parallel capacitor... As you changed frequency, since we normally
change the capacitor, you have to remotely change the parallel capacitor...
Ok.... So you have this rather large loop, inductor, and you have it's
parallel, capacitor you have to peak them (I believe I have already said
that).. Now. since our cable usually comes in 50 ohm impedances.... you have
to transport this weak signal to the radio, you have to use a split
capacitor.... the full capacitor is in parallel with the coil.... The ground
capacitor, of the two series capacitors, is adjusted to give the proper
match to the cable and the series capacitor is the parallel to the coil, you
have a very marvellous network of two capacitors, needing separate tuning to
keep this overall loop tuned...

A lot of work.... I just hope this loop antenna system can be used in both
transmit and receiver... (just my initial opinion)....

Any further thinking on this subject... you have my attention...

Larry ve3fxq



"Cecil Moore" wrote in message
...
larry wrote:
I might consider it...for 80 or 40...

How long is the loop in wavelengths?
--
73, Cecil http://www.qsl.net/w5dxp

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larry wrote:
A lot of work.... I just hope this loop antenna system can be used in both
transmit and receiver... (just my initial opinion)....

Full wave loops are quite different from small loops but both
can be used for both transmit and receive. As usual, transmit
is the challenge. A one-turn small loop works best if resonated
by a vacuum cap.

Any further thinking on this subject... you have my attention...

The ARRL Antenna Book has some good information on the subject.
Single turn loops work well for transmitting. Multiple turn
transmitting loops have a nasty habit of disappointing the user.
--
73, Cecil http://www.qsl.net/w5dxp


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It should be borne in mind the best form of radiator is just an
isolated straight length of wire. But curved or bent wires do almost
as good.

Loop antennas are nearly always single turn conductors and provide a
means of getting as much wire into space as possible with the largest
possible linear dimension being dependent on the size of your back
yard. Or your attic. Loops are space savers.

Subject to the space available, for a given perimeter, the larger the
area enclosed by a loop the better are its radiating properties and
its power efficiency. However, when an antenna is already 80 or 90
percent efficient, there is seldom any point in attempting to improve
it. 100 percent is impossible. And to improve it to 95 percent
results only in an entirely imperceptible 0.2dB or 1/20th of an
S-unit.

Again considering space requirements, the physically smallest loops
are descibed as Magloops. Magloops, not difficult to design, are the
most efficient of all small antennas of any type.

When the perimeter of a Magloop is only 1/3rd of a wavelength at the
operating frequency, efficiency can approach that of a full size
1/2-wave dipole. The disadvantage of a small magloop lies in its
restricted range of operating frequencies. Three adjacent HF bands at
most. The cost of a vaccuum variable capacitor cannot be neglected.

But even at frequencies as low as 1.9 and 3.6 MHz, magloops with
perimeters as small as 1/15 wavelengths, diameters as small as 1/50
wavelengths, are quite usable in small backyards and attics. Expect
signal strengths 2 or 2.5 S-units worse than a full size half-wave
dipole. There are reports of improved signal to noise ratio on receive
although I have not experienced this myself.

For design of magloops at any HF frequency and any reasonable size of
loop, download program MAGLOOP4 from website below.

For performance of much larger horizontal loops, for use in your
backyard, download program RJELOOP4
----
Reg, G4FGQ.

A follow-on from the previous message -

As usual, I forgot to mention the website from which the programs
could be downloaded. It may be something to do with a bottle of fine
vintage Port I have recently opened.

Download MAGLOOP4 and RJELOOP4 from website below and make what sense
you can out of them.

Incidentally, the number 4 in each name is an indication of previous
programs of similar names through which programs have been improved or
diverted.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Single turn loops work well for transmitting. Multiple turn
transmitting loops have a nasty habit of disappointing the user.
--
73, Cecil http://www.qsl.net/w5dxp

===================================

The reason a multi-turn maggloop of the same diameter would be
disappointing is because of increased loss in the loop conductor.

The ability to collect or radiate signals is a function only of the
diameter, ie., the longest linear dimension. Alternatively stated, a
function of the area enclosed.

With a single turn loop, conductor loss is due simply to skin effect.

With a multi-turn loop and the same amount of copper, proximity effect
comes into play and loss resistance increases faster than radiation
resistance.

Also, with a transmitting magloop, for the same power input, the
voltage across the tuning capacitor increases proportional to the
number of turns. Ridiculously high voltages appear. Although, the
value of the capacitor in pF is very much smaller, the physical size
of the capacitor remains the same.
----
Reg.