Topics

automatic magnetic loop adjustment


Miguel Angelo Bartie
 

Hi guys !

The video is here :
https://www.youtube.com/watch?v=kZiuSQSslhg

Sketch / schematics :(portuguese)
https://www.qsl.net/py2ohh/loopauto/loopauto.html

73 from py2ohh miguel


Mark Muller
 

Excellent Project!

For some reason, the link above did not work in my browser, and perhaps others might have the same problem. Hopefully this link is operational: https://www.qsl.net/py2ohh/trx/loopauto/loopauto.html

There seems to be some improvement to the original work here: https://www.qsl.net/py2ohh/trx/loopauto2/loopauto2.html 

Parabéns Miguel! 73 de N5KNG (Mark Muller)


Jack, W8TEE
 

Al Peter (AC8GY) and I have an article in the Feb. 2020 issue of Rad Com that describes our Double-Double Mag Loop:

Inline image

It is a 3' diameter loop, but the double configuration raises its efficient from about 10% to 50% on 40M and over 90% on 20M. We tested the remote control unoit at Field Day last year using 100' of cable and it worked fine. Tuning is done by Fast Tune (i.e., previously-stored values in EEPROM) and then fine tuned if necessary. All bands can get the SWR to 1.2 or less. The control unit uses the STM32F103 ("Blue Pill"). The cap can be air or vacuum (high power).

It's probably not a good choice for pedestrian mobile use, but those who face HOA restrictions might find it useful.


Jack, W8TEE






On Thursday, March 5, 2020, 1:48:26 PM EST, Mark Muller <markvmuller@...> wrote:


Excellent Project!

For some reason, the link above did not work in my browser, and perhaps others might have the same problem. Hopefully this link is operational: https://www.qsl.net/py2ohh/trx/loopauto/loopauto.html

There seems to be some improvement to the original work here: https://www.qsl.net/py2ohh/trx/loopauto2/loopauto2.html 

Parabéns Miguel! 73 de N5KNG (Mark Muller)

--
Jack, W8TEE


Murray Wills (ZL2IQ)
 

This looks fantastic Jack. Can’t wait to see the article. Murray ZL2IQ


From: BITX20@groups.io <BITX20@groups.io> on behalf of Jack, W8TEE via Groups.Io <jjpurdum@...>
Sent: Friday, March 6, 2020 9:58:36 AM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] automatic magnetic loop adjustment
 
Al Peter (AC8GY) and I have an article in the Feb. 2020 issue of Rad Com that describes our Double-Double Mag Loop:

Inline image

It is a 3' diameter loop, but the double configuration raises its efficient from about 10% to 50% on 40M and over 90% on 20M. We tested the remote control unoit at Field Day last year using 100' of cable and it worked fine. Tuning is done by Fast Tune (i.e., previously-stored values in EEPROM) and then fine tuned if necessary. All bands can get the SWR to 1.2 or less. The control unit uses the STM32F103 ("Blue Pill"). The cap can be air or vacuum (high power).

It's probably not a good choice for pedestrian mobile use, but those who face HOA restrictions might find it useful.


Jack, W8TEE






On Thursday, March 5, 2020, 1:48:26 PM EST, Mark Muller <markvmuller@...> wrote:


Excellent Project!

For some reason, the link above did not work in my browser, and perhaps others might have the same problem. Hopefully this link is operational: https://www.qsl.net/py2ohh/trx/loopauto/loopauto.html

There seems to be some improvement to the original work here: https://www.qsl.net/py2ohh/trx/loopauto2/loopauto2.html 

Parabéns Miguel! 73 de N5KNG (Mark Muller)

--
Jack, W8TEE


Miguel Angelo Bartie
 

Hello Mark Muller

I have 2 videos also:
first prototype :
https://www.youtube.com/watch?v=Si1GAlZDfq4&t=80s

And the best second video
https://www.youtube.com/watch?v=kZiuSQSslhg&t=2s

73 de py2ohh Miguel


Mark/airchecklover
 

Miguel,

I do not speak a word of Portugese but still could understand your video.  Excellent work my friend!

73, Mark

KD9NOO


Mark/airchecklover
 

Jack, I've been following your loop development and must congratulate you guys on doing everything right!  Great build quality.  You have gone to great lengths to optimize - or should I say minimize in terms of resistance - every aspect of signal flow.  That baby should come with a warning ....

EXTREME MAGNETIC FIELDS  PRESENT  :-)

 

What is the capacitor?  Range and voltage?  Antenna should handle how many watts?

(ha, or do I have to wait to find out ....)

 

73, Mark

KD9NOO


Jack, W8TEE
 

Mornin' Mark:

To cover 40M-20M, the cap needs to span about 15pF to 120pF. The one shown was tested to 200W with no arcing. There's a table in the ARRL handbook that discusses gap spacing and power, but I think ours is 3.5mm. If you're using a vacuum var cap at 100W, you would want at least 5KV rating.

I hope this helps!

73,
Jack, W8TEE

On Friday, March 6, 2020, 10:16:01 AM EST, Mark/airchecklover <mdh@...> wrote:


Jack, I've been following your loop development and must congratulate you guys on doing everything right!  Great build quality.  You have gone to great lengths to optimize - or should I say minimize in terms of resistance - every aspect of signal flow.  That baby should come with a warning ....

EXTREME MAGNETIC FIELDS  PRESENT  :-)

 

What is the capacitor?  Range and voltage?  Antenna should handle how many watts?

(ha, or do I have to wait to find out ....)

 

73, Mark

KD9NOO


--
Jack, W8TEE


Lou KI5FTY
 

Does anyone know a good source (low price) to get one.  I know these can be pricey.

Thanks

Lou KI5FTY

On Fri, Mar 6, 2020 at 9:35 AM Jack, W8TEE via Groups.Io <jjpurdum=yahoo.com@groups.io> wrote:
Mornin' Mark:

To cover 40M-20M, the cap needs to span about 15pF to 120pF. The one shown was tested to 200W with no arcing. There's a table in the ARRL handbook that discusses gap spacing and power, but I think ours is 3.5mm. If you're using a vacuum var cap at 100W, you would want at least 5KV rating.

I hope this helps!

73,
Jack, W8TEE

On Friday, March 6, 2020, 10:16:01 AM EST, Mark/airchecklover <mdh@...> wrote:


Jack, I've been following your loop development and must congratulate you guys on doing everything right!  Great build quality.  You have gone to great lengths to optimize - or should I say minimize in terms of resistance - every aspect of signal flow.  That baby should come with a warning ....

EXTREME MAGNETIC FIELDS  PRESENT  :-)

 

What is the capacitor?  Range and voltage?  Antenna should handle how many watts?

(ha, or do I have to wait to find out ....)

 

73, Mark

KD9NOO


--
Jack, W8TEE


Lawrence Galea
 


Sketch / schematics :(portuguese)
https://www.qsl.net/py2ohh/loopauto/loopauto.html  
Error 404 - Page Not Found

On Wed, Mar 4, 2020 at 6:39 PM Miguel Angelo Bartie via Groups.Io <py2ohh=yahoo.com.br@groups.io> wrote:
Hi guys !

The video is here :
https://www.youtube.com/watch?v=kZiuSQSslhg

Sketch / schematics :(portuguese)
https://www.qsl.net/py2ohh/loopauto/loopauto.html

73 from py2ohh miguel


Jack, W8TEE
 

What are you trying to buy. an air cap or a VVC? Also, for what power level. Consider:

Inline image

As you can tell from the full-sized keyboard in the background, the top one could be used as a bread slicer and has a range from 43pF to 325pf with a 0.11mm gap and has a gear assembly on it. (The cap would likely have to be modified slightly to cover the complete 40-20M range.)  The small one on the left is 12pF to 156pF with a 0.06mm gap and the remaining one is 27pF to 488pF with a 0.03mm gap. I have them priced at $85, $10, and $45 respectively (postage extra). The lower-right is brand new and the other two were picked up in the infield at Xenia.

Anyway, this should give you an idea of what things might cost for air caps. I did manage to pick up a nice small 15pF-180pF, 5KV VVC in Xenia last year for $80, but most VVC's will run around $100.

Jack, W8TEE



On Friday, March 6, 2020, 2:01:41 PM EST, Lou KI5FTY <lscalpati@...> wrote:


Does anyone know a good source (low price) to get one.  I know these can be pricey.

Thanks

Lou KI5FTY

On Fri, Mar 6, 2020 at 9:35 AM Jack, W8TEE via Groups.Io <jjpurdum=yahoo.com@groups.io> wrote:
Mornin' Mark:

To cover 40M-20M, the cap needs to span about 15pF to 120pF. The one shown was tested to 200W with no arcing. There's a table in the ARRL handbook that discusses gap spacing and power, but I think ours is 3.5mm. If you're using a vacuum var cap at 100W, you would want at least 5KV rating.

I hope this helps!

73,
Jack, W8TEE

On Friday, March 6, 2020, 10:16:01 AM EST, Mark/airchecklover <mdh@...> wrote:


Jack, I've been following your loop development and must congratulate you guys on doing everything right!  Great build quality.  You have gone to great lengths to optimize - or should I say minimize in terms of resistance - every aspect of signal flow.  That baby should come with a warning ....

EXTREME MAGNETIC FIELDS  PRESENT  :-)

 

What is the capacitor?  Range and voltage?  Antenna should handle how many watts?

(ha, or do I have to wait to find out ....)

 

73, Mark

KD9NOO


--
Jack, W8TEE


--
Jack, W8TEE


Jerry Gaffke
 

I suspect the dimensions Jack gives here are in inches, not milimeters.

RF currents in a mag loop can be astonishingly large when at above QRP power levels.
For the caps shown in the photo, those currents have to go through the rotor bearings.
For a mag loop, many find it works much better if the cap has two sets of stator plates,
the rotor plates provide the connection between the two sets of stator plates and there
is no current through the rotor bearings.  Effectively two variable capacitors in series.

Jerry, KE7ER



On Fri, Mar 6, 2020 at 12:05 PM, Jack, W8TEE wrote:
As you can tell from the full-sized keyboard in the background, the top one could be used as a bread slicer and has a range from 43pF to 325pf with a 0.11mm gap and has a gear assembly on it. (The cap would likely have to be modified slightly to cover the complete 40-20M range.)  The small one on the left is 12pF to 156pF with a 0.06mm gap and the remaining one is 27pF to 488pF with a 0.03mm gap. I have them priced at $85, $10, and $45 respectively (postage extra). The lower-right is brand new and the other two were picked up in the infield at Xenia.
 
Anyway, this should give you an idea of what things might cost for air caps. I did manage to pick up a nice small 15pF-180pF, 5KV VVC in Xenia last year for $80, but most VVC's will run around $100.


Kees T
 

Jack, nice looking loop antenna. Looks like that is essentially a 2 turn 1M? loop, same as what the AQRP group has been experimenting with.  I was using 2 turns for 80m/40m and tried several schemes for making it 1 turn for the higher (20m and up) bands but could never figure out a workable, low joint resistance and low resistance switching scheme. Do you know what the RF resistance at the operating frequencies is for your antenna ? Have you measured the effect of the parallel turns since the effective inner currents between the two tubes cancel and the surface current is largely on the outer perimeter of the tubing "8".  The bands 20m and up are much easier than 80m/40m. 

Are the joints silver soldered to lower resistance ? Using the two variables, like I see in the picture, can remove the high current from the variable bearings but it cuts the capacitance value in half.  I have found as much of a resistance problem is how the plates are attached to the shaft (MFJ variables are terrible). The really need to be welded but that requires special welding. I wonder if this low temp solder they advertise using a propane torch would work ??  

Since all good loop antennas require an antenna tuner like Loftur TF3LJ offers or PY2OOH with his Nano based tuner, I am assuming you have the "blue Pill" antenna tuner. Any more info on that ? Do you perform a canned rough frequency "preset" and then fine tune ?

Sorry about all the questions but I am interested.

73 Kees K5BCQ


Kees T
 

We also tried using 10ft sections of large (2" +) copper hard tubing from Lowe's but the local muffler shops didn't want to run it through their equipment to make a circle. And we looked into the much larger copper rain gutter downspout which would be ideal but ran into the same bending problem. So we went back to a roll of soft copper tubing after trying (really cheap) surplus hardline. However ..... Didn't try to "solder" that hardline with the material I discussed earlier.

73 Kees K5BCQ  


Kees T
 

I'm confused.....and need a better explanation on how that double tubing conductor works. From the picture, looks like the two are in parallel with the current flowing in the same direction.....but you still have the  maximim RF current on the outside of the figure "8" . Maybe the spacing between the two is sufficient to not force most of the RF current to the outside ?

A lot of loop designers using a strip of metal don't realize that the high RF current density is on the opposite edges of the strip with minimum RF current density on the center of the strip. And all that drives the RF resistance of the loop which is a killer at the lower frequencies.

73 Kees K5BCQ


Jack, W8TEE
 

Both of your emails suggest that perhaps you should read the article.

Jack, W8TEE


On Friday, March 6, 2020, 9:36:58 PM EST, Kees T <windy10605@...> wrote:


I'm confused.....and need a better explanation on how that double tubing conductor works. From the picture, looks like the two are in parallel with the current flowing in the same direction.....but you still have the  maximim RF current on the outside of the figure "8" . Maybe the spacing between the two is sufficient to not force most of the RF current to the outside ?

A lot of loop designers using a strip of metal don't realize that the high RF current density is on the opposite edges of the strip with minimum RF current density on the center of the strip. And all that drives the RF resistance of the loop which is a killer at the lower frequencies.

73 Kees K5BCQ

--
Jack, W8TEE


Jack, W8TEE
 

No, they are in mm, I just screwed up the decimal points! Al discusses the modifications that may be required for the proper range in the article. In the book, he also tells how to modify air variable caps to better-suit the needs of the bands being considered.

Jack, W8TEE

On Friday, March 6, 2020, 7:57:47 PM EST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:


I suspect the dimensions Jack gives here are in inches, not milimeters.

RF currents in a mag loop can be astonishingly large when at above QRP power levels.
For the caps shown in the photo, those currents have to go through the rotor bearings.
For a mag loop, many find it works much better if the cap has two sets of stator plates,
the rotor plates provide the connection between the two sets of stator plates and there
is no current through the rotor bearings.  Effectively two variable capacitors in series.

Jerry, KE7ER



On Fri, Mar 6, 2020 at 12:05 PM, Jack, W8TEE wrote:
As you can tell from the full-sized keyboard in the background, the top one could be used as a bread slicer and has a range from 43pF to 325pf with a 0.11mm gap and has a gear assembly on it. (The cap would likely have to be modified slightly to cover the complete 40-20M range.)  The small one on the left is 12pF to 156pF with a 0.06mm gap and the remaining one is 27pF to 488pF with a 0.03mm gap. I have them priced at $85, $10, and $45 respectively (postage extra). The lower-right is brand new and the other two were picked up in the infield at Xenia.
 
Anyway, this should give you an idea of what things might cost for air caps. I did manage to pick up a nice small 15pF-180pF, 5KV VVC in Xenia last year for $80, but most VVC's will run around $100.

--
Jack, W8TEE


Miguel Angelo Bartie
 

Hi Lawrence and friends

The correct lik is :
https://www.qsl.net/py2ohh/trx/loopauto/loopauto.html

and the update :
https://www.qsl.net/py2ohh/trx/loopauto2/loopauto2.html

Use translator to read.

73 de py2ohh miguel


Andy_501 <andrew.webb.501.ve4per@...>
 

FWIW

I used 16.5 ft of surplus used 3/4 in. heliax. Stripped outer rubber cover off to keep it physically lighter.  designed mine for 20 M. Used ABS/PVC water pipe tee, union and support pipe to close loop.

If that is any help.   FYI here is design calculator page  http://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx

pardon  me if not directly related to discussion at hand as I am in on exchange midway through.

cheers & 73


On 2020-03-06 8:11 p.m., Kees T wrote:
We also tried using 10ft sections of large (2" +) copper hard tubing from Lowe's but the local muffler shops didn't want to run it through their equipment to make a circle. And we looked into the much larger copper rain gutter downspout which would be ideal but ran into the same bending problem. So we went back to a roll of soft copper tubing after trying (really cheap) surplus hardline. However ..... Didn't try to "solder" that hardline with the material I discussed earlier.

73 Kees K5BCQ  


Lawrence Galea
 

TNX


On Sat, Mar 7, 2020 at 10:58 AM Miguel Angelo Bartie via Groups.Io <py2ohh=yahoo.com.br@groups.io> wrote:
Hi Lawrence and friends

The correct lik is :
https://www.qsl.net/py2ohh/trx/loopauto/loopauto.html

and the update :
https://www.qsl.net/py2ohh/trx/loopauto2/loopauto2.html

Use translator to read.

73 de py2ohh miguel