Topics

Availability of Mag Loop and other stuff...

ajparent1/KB1GMX
 

ITs cleverly hidden...

T1 and R4 and 3/4ths of the bridge the antenna is the other leg.  The centertap of the
transformer will have zero RF(noise) if the antenna leg has the exact same resistance
and reactance as R4.  What most expect to be resistors are the two halves of the
trifilar wound (three identical windings) transformer.

If R4 is made variable you can measure the impedance in the other leg.  The Palomar
(and others) device adds a variable capacitance to allow measuring the reactance
as well.  When R,jX are equal to the other leg then you can directly read it from a
calibrated scale.

For interest or if you plan to make on two articles one for the Palomar and another
on building and using.

The noise bridge was the pre-MFJ-259B device that was available and
more accurate.


Allison

Bo Barry <bobarr@...>
 

I don't understand the 'bridge' in the first one. I don't see the Whetstone bridge!  
Going to look over the pair of items.
I have more antenna analyzers than most hams have rigs!
--
Bo W4GHV - since '54

Bo Barry <bobarr@...>
 

Nice long article, thanks!   
You offering it in kit form? 🤔😂

I love the one I got.  Set rig to desired freq, set bridge to 50 ohms, XL-XC to center and tune mag loop for quiet.
Or for existing antenna it gives the R and then if the antenna is too short or long at your tuned freq. Nice.
--
Bo W4GHV - since '54

Tom, wb6b
 

On Mon, Jun 3, 2019 at 12:31 PM, Kees T wrote:
Speaking of using Noise Bridges, there is an excellent one by N6DT
I recently received this noise source and "reflection" bridge to do antenna testing.

https://www.ebay.com/itm/ORIGINAL-RF-SWR-Reflection-Bridge-0-1-3000-MHZ-Antenna-Analyzer-VHF-UHF-VSWR/292083525131

https://www.ebay.com/itm/2018-new-version-noise-source-Simple-spectrum-external-tracking-source/111392810099

Tom, wb6b

ajparent1/KB1GMX
 

Bo,

I have the Palomar noise bridge unit and its a very useful tool.
Worth way more than the price I paid for it (1$ at a flea).

Allison

Kees T
 

Bo,

Speaking of using Noise Bridges, there is an excellent one by N6DT
http://www.nd6t.com/antenna/Polite%20Tuner.htm

ajparent1/KB1GMX
 

A SWR of 1:1 is easy with a dummy load but as a radiator its efficiency is very poor.
Some antennas can be matched to a good SWR and still be poor radiators.

SWR is not a measure of antenna effectiveness or efficiency its a statement of
how well the load is matched to the source.

So where does the energy go, mostly heat.  the comment I hear often, I I can
measure no warming, completely missing that all that copper or aluminum
will radiate heat well. 

Allison

Bo Barry <bobarr@...>
 

My conclusion so far is that the mag loop is fun, educational, amazing especially that it does work indoors, does a pretty decent job on FT8, is A solution for HOA owners ( gutter or hidden EFHW are BETTER Solutions), AND in NO way compete with full size antennas. 

P.S. I've found an old Palomar Engineering noise bridge to be the very best way of tuning!  Found on eBay. It does both X and R.
--
Bo W4GHV - since '54

iz oos
 

Just for curiosity, I have simulated (the same link suggested by LNR or PARelectronics) a no brand small loop I bought from a hamfest. It is for 2M, when I bought I was told efficient at 95%, SWR=1 at 145Mhz. Actually SWR was perfect but I was never impressed... simulated results show a negative gain around -20db!!! Not exactly the same value said by that vendor... Where does all this energy go???


Il 03/giu/2019 04:08, "ajparent1/KB1GMX" <kb1gmx@...> ha scritto:
Radiation pattern of the reference antenna EFHW varies with frequency. 

Loops however are very predictable and the pattern is well understood and
does not change with frequency until it no longer a small loop, its why they
are used.

A multi turn loop has a lower frequency to size (total lenght) where the pure loop
behavior departs from the predicted.  Its easy to see that as the deep nulls are no
longer along the though axis.  By then a smaller loop is likely desirable.

The whole 2M thing was a frequency where testing can be done without great
time and expense.  One does not have to be interested in the higher frequency
to get useful and accurate data.   It is a common practice in the industry to scale
to a frequency where its easy to do the needed testing in smaller spaces or even
a metallic or wood work surface.  

I do have a 144mhz (4 inch diameter) tuned loop for noise DF (RX only or under 1W)
and the nulls allow me to determine where on a pole a noise source is once I know
which pole.  Very sharp nulls.

In general two costly items are the cap and if padding caps are used suitable high
voltage and high current fixed value caps of decent Q.     The element is copper
tube and not a high price item considering how much is required.  Copper is
preferred over aluminum as aluminum has a higher resistance and if oxidized
(its normal state) the oxide surface s a near insulator.  Also copper can be hard
soldered (silver alloy) using MAPP gas torch.   

Allison

ajparent1/KB1GMX
 

Radiation pattern of the reference antenna EFHW varies with frequency. 

Loops however are very predictable and the pattern is well understood and
does not change with frequency until it no longer a small loop, its why they
are used.

A multi turn loop has a lower frequency to size (total lenght) where the pure loop
behavior departs from the predicted.  Its easy to see that as the deep nulls are no
longer along the though axis.  By then a smaller loop is likely desirable.

The whole 2M thing was a frequency where testing can be done without great
time and expense.  One does not have to be interested in the higher frequency
to get useful and accurate data.   It is a common practice in the industry to scale
to a frequency where its easy to do the needed testing in smaller spaces or even
a metallic or wood work surface.  

I do have a 144mhz (4 inch diameter) tuned loop for noise DF (RX only or under 1W)
and the nulls allow me to determine where on a pole a noise source is once I know
which pole.  Very sharp nulls.

In general two costly items are the cap and if padding caps are used suitable high
voltage and high current fixed value caps of decent Q.     The element is copper
tube and not a high price item considering how much is required.  Copper is
preferred over aluminum as aluminum has a higher resistance and if oxidized
(its normal state) the oxide surface s a near insulator.  Also copper can be hard
soldered (silver alloy) using MAPP gas torch.   

Allison

Jack, W8TEE
 

You're probably right, but as Allison pointed out, the radiation pattern varies with frequency and, quite honestly, I have little interest in 2M. We will be doing some experiments and readers can choose to digest or ignore what we report.

Jack, W8TEE

On Sunday, June 2, 2019, 1:54:29 PM EDT, iz oos <and2oosiz2@...> wrote:


Maybe it would be easier to test if made for the 2m band and compare with a ground plane and a dipole at different heights.
It is interesting the link https://www.lnrprecision.com/store/W4OP-Loop-Antenna-p69633466 which deals with the efficiency of commercial small loops. If you can really obtain a small loop with a 50% efficiency I would be really interested to know more about it.


Il 02/giu/2019 19:20, "Arv Evans" <arvid.evans@...> ha scritto:
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

Kees T
 

Fellow Loopers, guess "BITX20" is where it's at

a few thoughts....

Definition of a SML
1)  Let's say we want to stay closer to a 1M Loop.....maybe 40" to 48" diameter which is "relatively portable".  
2) Goal is 80m to 10m

Select a Band(s)
3) For 80m we probably need 2 turns separated by 10 tubing diameters (my rule of thumb...what is yours ?)
4) A single loop for 40m to 20m is fine, 17m and up is TBD
5) Loop switching is TBD

AC Loop resistance (KEY parameter).
6) Lowest reasonable tubing material for lowest resistance.....Copper vs Aluminum. That info is widely available. Cost,
    weight, and availability tradeoffs. Aluminum hardline is readily available and very inexpensive used. Copper can cost
    quite a bit used or not. You need TIG welding for aluminum.
7) Lowest number of joints and lowest resistance joints....bolted, soldered, silver soldered, brazed, welded. Does anyone
    have some measurement data for say .....a 2" wide joint with a 1/2" overlap at 80m.  We're talking milliohms and less
    here......yes, it is important in order to increase efficiency. You need TIG welding for aluminum.
8) Tubing material shape, assume round tubing. The larger the better.....up to a point where you start having RF current
    flow interference. A large donut shape does not work well, neither does anything flimsy due to wind effects (In my
    opinion).
9) Flat strap "tubing". The high current density is in the outside edges of the strap, not across the full width of the strap, 
    so if the strap is thin, the material conductive properties come into play.....bigtime. 
10) Using several (5?, 7?) identical hardline (cheap) loops as a sturdy form, cover them with thin copper sheeting, say 10"
    wide and running along the circumference of the loop. Curved (cupped) a little in the center. Do not spiral wind the
    copper sheeting due to the resultant seams. The idea here is to force the RF current density to the "wide" outside side of
    the copper. The other idea here is no serial seams except at the ends. A seam running the full inside diameter is OK and
    minimize copper sheeting wrinkles. Attach 1ft ? copper plates at the ends for the capacitor. (just some ideas).  Air
    spacing or Teflon sheeting for the dielectric.

The Capacitor
11) Many tradeoffs on the capacitor. One full range capacitor or several switched capacitors and a smaller "trimmer".....but
    again all contacts are going to add to the overall loop resistance and switching implementation will not be simple.

The Coupler

12) Allow for BOTH rotation of the coil and movement relative to the loop circumference.  

The Testing
13) I would recommend that someone in your group buy a commercial loop antenna to use as a reference
      antenna.

73 Kees K5BCQ

ajparent1/KB1GMX
 

Iz oos.

To get to 50% just make it bigger.  The cost is more material and size plus higher Q
makes tuning fussy.   A 3M diameter will do for 20m and at 40M you need to be
about 8m which is getting large.

Allison

ajparent1/KB1GMX
 

Jack,

Not aimed at you personally that was a general comment on some of the other loop vendors
that came from nowhere.  After all at this point you not selling anything.  If you telling people
how to do it [book] that's experimental electronics and encouraged.  

As to getting HOA/restricted people back on the air a loop is a possible choice but far from
the only one.  It has potential for a quick trip to the park, hill or other areas where ambient
electrical noise is much lower and its desirable to have minimal setup time.   Usually the
limitation is lack of imagination and maybe understanding of antennas in general.  Antennas
do not have to look like antennas and they can be reasonably efficient with a small amount
of work.  The key element is to look at the box and not be limited by it.  The biggest thing I
see is everyone wants every band even the inactive ones.  Two maybe three bands with a
reasonable antenna is far easier and more likely to be enjoyed.  

And being 10db down from a "good" antenna is not a crime.  I've worked a lot of DX from the
mobile on 40M QRP SSB with a center loaded 8ft whip.  Efficient?  No they are legendary for
being terrible as in easily 10db or more down from a full size vertical.  However the mobile is not
unlike the HOA, we just add it has to work at 80mph and clear a 12.6ft bridge (we have
low ones here!) when mounted on a truck more than 4ft above the road with a crappy
ground (counterpoise maybe?).  

As to commentary on exogenous factors, when you quote dB and people look at it without
understanding or knowledge of those factors it can look better than it is.  Fact is and I
already said that you cannot control the external factors as it would cost dearly, having
done it for MIL applications and budget.

Also I think it was Arv that suggested scaling it for low VHF and that can be done to show if
correlation holds true but its a lot of work to make a scale model and  test it against a vertical
dipole. 

I've done that and it can be close (usually +-1db) and the amount of room needed is a back
yard without metal fences or aluminum siding as reflections will make you nuts. Reflections
can make for errors as in higher or lower gain that should be expected.   The test is RF
source to a vertical dipole and a second dipole at a distance of 10-20M at 2m will do ok
and you get a RX measurement that will be the reference.  Dipoles vertical or horizontal if
resonant are predictable in gain and behavior.  A pair of ELK log periodic antennas would
work well for this, they just have to be the same.  I've used 4 element yagis for 2m and
432 as test antennas as they are simple and easy to make.  In any case directional
antennas  make for fewer issues with weak signals and reflections.    Now substitute the
antenna under test and  get new reading.   How to get an accurate reading is easy, on the
TX side use maybe 20dbm (100mw) and an attenuator to radiate a signal to the RX and
then use the attenuator as adjust the signal to S9. install new antenna at the RX end and after
recording the attenuator before then adjust it for S9 again.  The difference is gain or loss.
A SA can make that easier but any detector can do the job if sensitive enough and has
selectivity to avoid offending signals.  I've used a AD8703 for that with an input tuned
circuit [bandpass] added to keep it from hearing FM broadcast stations.    Don't try this
at HF you will go insane or expend much treasure and going end to end to read or
adjust will wear you out.

Allison

iz oos
 

Maybe it would be easier to test if made for the 2m band and compare with a ground plane and a dipole at different heights.
It is interesting the link https://www.lnrprecision.com/store/W4OP-Loop-Antenna-p69633466 which deals with the efficiency of commercial small loops. If you can really obtain a small loop with a 50% efficiency I would be really interested to know more about it.


Il 02/giu/2019 19:20, "Arv Evans" <arvid.evans@...> ha scritto:
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

Arv Evans
 

Ian

As much wire in the air as is physically possible is a good approach, as long as one has
many acres of open space to work with.  Loop antennas are effective enough for those of
us with HOA restrictions to get on the air, even if we have to hide the antenna in the attic. 
Loop antenna efficiency does increase with increasing size.  Size versus efficiency is a
trade-off that we sometimes have to live with. 

Small loops can be rotated in a small space and can even be rotated from vertical to
horizontal orientation, and anywhere in between.  Doing that with a 7 wavelength rhombic
antenna on 80 meters may be a little difficult.  8-)

Arv
_._


On Sun, Jun 2, 2019 at 11:34 AM Ian Reeve <ian.radioworkshop@...> wrote:
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

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

Arv Evans
 

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

Ian Reeve
 

Spent some time with a low budget may loop made from straight pieces of thick aluminium strip bolted in a hexagon shape with a remote tune function fed by a separate coax cable from a 12v supply.Deliberately designed to add a little resistance to the "loop" to reduce the spacing on the variable tuning capacitor,it worked.Hanging it from a tree branch it proved to receive signals two s points below my half size windom.Transmit showed a similar pattern.No efficiency figures for either antenna,just receive and transmit reports.The transceiver used a k3 at 100 watts at the input to the power/swr meter.There are some very fancy loops around at equally fancy prices but it seems to me a loop of copper pipe( 6 or 8mm diameter central heating radiator supply) of 1 meter overall diameter would be a good starting point.I understand that the lest resistance in the loop is paramount and therefore a massive voltage will be across the tuning capacitor which ideally needs to be of the vacuum sort.Either way the loop is resonant over a very narrow band and a being directional,useful to reduce troublesome qrm.As to efficiency,I will leave the calculations to the folks who know.


From: BITX20@groups.io <BITX20@groups.io> on behalf of Jack Purdum via Groups.Io <jjpurdum@...>
Sent: Sunday, June 2, 2019 5:35:38 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Availability of Mag Loop and other stuff...
 
"However taking peoples money with inaccurate or extravagant claims should not be a hobby, though it is often a vocation people pursue."

Taking people's money? I'm not selling anything. My real goal is to get people constrained by HOA's or spouses back on the air.

Jack, W8TEE


On Sunday, June 2, 2019, 12:10:18 PM EDT, ajparent1/KB1GMX <kb1gmx@...> wrote:


Arv,

The problem of online RX or for that fact QRSS and WSPR sites is antenna alignment.
If you antenna is not "aimed" that way the result is it could have been a long path or worse
"off the side".  They do help with "have you been heard" and allows estimating propagation 
in a given direction but comparing A and B antennas requires care for both aim and
time of comparison as propagation is a transient thing.

MY 0.02$ on hobby, it is!  However taking peoples money with inaccurate or
extravagant claims should not be a hobby, though it is often a vocation people
pursue.  When people want to enjoy the hobby and are limited in time and budget
accuracy and good explanation is helpful.  When one expends time and money
on a course of action or material its desirable to understand what the outcome
may be or the limitations.

So every time a new antenna fad hits we have this.  Loops are indeed useful.
They are compact, self contained, and in some cases can help with local noise.
The yabut is they are very narrow band if they are as efficient as possible and
that leads to remote tuning as they are touchy and requiring SWR monitoring.
Being small antennas they are still low gain and therefor not the ultimate radiator. 
However the idea that I can get a loop and conquer the world from my garden
is loaded for disappointment as even the cheapest loop cost hundreds of
dollars and they most expensive ones are not that much better.  I've looked at
commercial loops and they are in the range of 199$ to well over 500$  that is
a lot of money to get an antenna that may be only passable or worse that it
can't work indoors in a building with metallic handicaps (stucco with wire, metal
framing, aluminum siding,  and foil backed insulation).  You have to keep it a
reasonable distance away from the radio so RF problems do not result.

As to building ones own, a good design wants a vacuum variable and they
are NOT cheap.  Air variables of the dual rotor forma can work ok but still
if you have to buy one they are costly.  Also the cap used determines max
power and tuning range as it had to withstand very high voltages even
at QRP levels.

That said if your junk box can full the need its interesting to experiment with Loops.


Allison

Jack, W8TEE
 

"However taking peoples money with inaccurate or extravagant claims should not be a hobby, though it is often a vocation people pursue."

Taking people's money? I'm not selling anything. My real goal is to get people constrained by HOA's or spouses back on the air.

Jack, W8TEE


On Sunday, June 2, 2019, 12:10:18 PM EDT, ajparent1/KB1GMX <kb1gmx@...> wrote:


Arv,

The problem of online RX or for that fact QRSS and WSPR sites is antenna alignment.
If you antenna is not "aimed" that way the result is it could have been a long path or worse
"off the side".  They do help with "have you been heard" and allows estimating propagation 
in a given direction but comparing A and B antennas requires care for both aim and
time of comparison as propagation is a transient thing.

MY 0.02$ on hobby, it is!  However taking peoples money with inaccurate or
extravagant claims should not be a hobby, though it is often a vocation people
pursue.  When people want to enjoy the hobby and are limited in time and budget
accuracy and good explanation is helpful.  When one expends time and money
on a course of action or material its desirable to understand what the outcome
may be or the limitations.

So every time a new antenna fad hits we have this.  Loops are indeed useful.
They are compact, self contained, and in some cases can help with local noise.
The yabut is they are very narrow band if they are as efficient as possible and
that leads to remote tuning as they are touchy and requiring SWR monitoring.
Being small antennas they are still low gain and therefor not the ultimate radiator. 
However the idea that I can get a loop and conquer the world from my garden
is loaded for disappointment as even the cheapest loop cost hundreds of
dollars and they most expensive ones are not that much better.  I've looked at
commercial loops and they are in the range of 199$ to well over 500$  that is
a lot of money to get an antenna that may be only passable or worse that it
can't work indoors in a building with metallic handicaps (stucco with wire, metal
framing, aluminum siding,  and foil backed insulation).  You have to keep it a
reasonable distance away from the radio so RF problems do not result.

As to building ones own, a good design wants a vacuum variable and they
are NOT cheap.  Air variables of the dual rotor forma can work ok but still
if you have to buy one they are costly.  Also the cap used determines max
power and tuning range as it had to withstand very high voltages even
at QRP levels.

That said if your junk box can full the need its interesting to experiment with Loops.


Allison