Re: Availability of Mag Loop and other stuff...

Ian Reeve
 

Hi Arv,  Very useful information and so useful that they can be used any orientation,they are a option but as my amateur radio course tutor says....you need as much wire in the sky as you can get....as a stating point to good Hf receive.


From: BITX20@groups.io <BITX20@groups.io> on behalf of Arv Evans <arvid.evans@...>
Sent: Sunday, June 2, 2019 6:19:39 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Availability of Mag Loop and other stuff...
 
Antenna measurements are for the most part relative to some measured reference signal between
the antenna being tested and the remote reception point.  Antenna at the remote reception point
would seem to be immaterial as long as it does not change characteristics during the tests.  In most
antenna test ranges it is the device being tested that is rotated with the received signal at a fixed
point being measured.  This allows measurement and documentation of signal levels at various
angles of radiation.  Rotating or moving the receiving site is not necessary and would probably
invalidate the measurements. 

Small loop antennas are interesting for another reason.  They can be mounted and measured in
either horizontal or vertical position relative to the local ground plane, or at any angle in between. 
This gives one an idea of which propagation angle might be more advantageous, but only an
idea of that.  Propagation at later dates may totally invalidate any reference measurements that
have been made and published. 

My 2 pence worth. 

Arv
_._


On Sun, Jun 2, 2019 at 9:39 AM ajparent1/KB1GMX <kb1gmx@...> wrote:
Jack,

Not showing off, no one is paying for it.  However when someone claims a loop
that 1-2db below a EFHW (or a dipole) that's pretty close to saying my 10 year
old Tacoma can win at Indy.  In short, not likely or the Indy cars had an unusual
handicap, like no fuel and must be pushed by pit crew.   Reality is that the EFHW
is pointed in some random direction relative to the station and the loop is aimed
though its 3db beam width is likely far wider than the EFHW or a standard dipole
at reasonable height.  That makes its aim very wide where a 80-10 EFHW on
40M will at best have a pattern with a beam width that is narrow as its 1
wavelength long.   I can claim and prove my square loop on 6M at 7ft is better
than my portable 6M full wave length rectaangle loop at 25ft  by pointing the
edge of the loop to the station at distance as the front to side is easily 20db
down.  For that I'm at least the same horizontal polarization.  The square loop
under that condition is about 14db better however if the big loop is aligned its
4 db worse.  In short that proves the big loop does really work and also proves
the omnidiriectional square loop is superior when omnidirectional coverage
is required.

In short comparing it to any antenna without some form of controls and claiming
performance is at best meaningless.    A valid compare is a full size vertical with
elevated radials as it will have known gain and similar takeoff angles.

Loops are cool antennas but they are small antennas and they nominally will be
negative gain compared to any dipole.  Its the nature of antenna compromise.

Fyi: the testing part is to show how difficult it is to get meaningful real world
test data with any accuracy at HF because of distances and even local
surface propagation.   Modeled is of value but care must be taken to use a 
model that works with small loops and real grounds (NEC4.2 engine).

As to helpful.  Yes I want people to realize the limits of small antennas and
the claims sometimes made that are against all modeled data and practical
theory never minding prior works done to verify the models.  To that I see a
lot of suppliers and articles for loops making claims like this is the new
better sliced bread.  

I use loops and I do apply them as they have characteristics that make
them useful.  First being they are self contained antennas. The other
feature is the nulls and their insensitivity to close in electrostatic fields.
Its what they are good at even when they are full sized 1lambda loops.

Allison

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