Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: More magnet loop questions  (Read 16797 times)
RSHIRE22
Member

Posts: 0




Ignore
« on: November 12, 2013, 02:25:19 PM »

This is a follow up to my previous question. I instead  have decided to build a magnetic loop antenna using aluminum bar for the loop due to it's economy and it's ease of use compared to copper.


Band: 20 meters

Loop material: 10 - 1 ft sections of 1 foot long, 1' wide, 1/8' thick aluminum bar bolted together.

Feed: FT240-43 ferrite core fed with coax.

My questions are:

1) Does 1" by 1/8" aluminum bar act as a 1' diameter conductor (due to skin effect) or as a smaller diameter due to the  1/8 " narrow width?

2) Since the 1' inch width of the aluminum bar is in the plane of the directional axis rather than at cross angle will this negatively affect the efficiency?

Thank you for your replies in advance.

Ron
Logged
RSHIRE22
Member

Posts: 0




Ignore
« Reply #1 on: November 12, 2013, 02:40:33 PM »

Oops. I just got my answer. I'll just build it so the 1' aluminum strip is perpendicular to the direction of axis. Current probably flows at less than 1/8' depth at 14mhz.

Ron
Logged
WB6BYU
Member

Posts: 15347




Ignore
« Reply #2 on: November 12, 2013, 03:05:12 PM »

A first-order approximation of the RF resistance would be based on the surface area
of the conductor, assuming the thickness was greater than the skin depth.  In that
case a 1" wide flat strip (with 2" of effective surface width) would be similar to
5/8" diameter tubing (also having 2" of surface width.)


If you were designing yagis using the flat strip then you would use a different
correction factor based on the resonant length of different shapes.  W9CF has a
calculator for that here:  http://fermi.la.asu.edu/w9cf/equiv/index.html
Logged
VE3WMB
Member

Posts: 310




Ignore
« Reply #3 on: November 28, 2013, 05:42:22 AM »


From an efficiency perspective you would be far better off to use 3/8 to 1/2 inch copper tubing rather than short lengths of AL. The key to building an efficient Loop is to minimize or eliminate
Mechanical connections as these will add significant losses. Also for the same sized loop material copper is about 25 to 30 percent less resistive. Soft copper tubing is available in rolls up to 50 ft in
Length and is quite easy to work with. I suggest you join the MAGLOOP Yahoo group as there are
Lots off good resources and knowledgable people on the list to answer questions.

Cheers

Michael VE3WMB

This is a follow up to my previous question. I instead  have decided to build a magnetic loop antenna using aluminum bar for the loop due to it's economy and it's ease of use compared to copper.


Band: 20 meters

Loop material: 10 - 1 ft sections of 1 foot long, 1' wide, 1/8' thick aluminum bar bolted together.

Feed: FT240-43 ferrite core fed with coax.

My questions are:

1) Does 1" by 1/8" aluminum bar act as a 1' diameter conductor (due to skin effect) or as a smaller diameter due to the  1/8 " narrow width?

2) Since the 1' inch width of the aluminum bar is in the plane of the directional axis rather than at cross angle will this negatively affect the efficiency?

Thank you for your replies in advance.

Ron
Logged
KC4MOP
Member

Posts: 912




Ignore
« Reply #4 on: December 01, 2013, 05:20:32 AM »

Here's something I built. A 72" helically wound loop antenna......QRO power handling. A very different approach. It works. The usual A-B comparisons with other antennas. Yagi and Dipole. But for only 6 feet from the ground and barefoot power, I was able to have a surprise QSO with a Ham (SL58???) in Slovenia, on 40M. There was a slight increase in our signals when I switched to a rotatable dipole 65 feet in the air.
Another advantage is how nice and quiet a magnetic loop antenna is on RX.

http://www.eham.net/articles/26572

The WX is slowing me down to build the 33" dia loop for 20-10M
Fred
Logged
KB4QAA
Member

Posts: 3064




Ignore
« Reply #5 on: December 01, 2013, 08:25:39 AM »

Small loops I2R law means that even small resistances mean big losses.  

-Aluminum is lossier than copper
-Bolted connections will mean big loss in the loop and at the connection to the variable capacitor.   Whenever possible continuous components and soldered connections must be used.

-Flat stock has smaller surface area and greater losses than tube stock.

Small loops are a special case in antenna  design with little tolerance for error.  Don't expect to slap one together, or modify the design and expect good (or even useable) performance.   I recommend careful study of QST articles and the ARRL Antenna Handbook before wasting effort and money in this field.  73, bill

p.s.  Beware of crank designs on the internet including some that claim winding helical elements over plastic tubing are equivalent!


« Last Edit: December 01, 2013, 08:29:17 AM by KB4QAA » Logged
KC4MOP
Member

Posts: 912




Ignore
« Reply #6 on: December 01, 2013, 03:36:30 PM »

Small loops I2R law means that even small resistances mean big losses.  

-Aluminum is lossier than copper
-Bolted connections will mean big loss in the loop and at the connection to the variable capacitor.   Whenever possible continuous components and soldered connections must be used.

-Flat stock has smaller surface area and greater losses than tube stock.

Small loops are a special case in antenna  design with little tolerance for error.  Don't expect to slap one together, or modify the design and expect good (or even useable) performance.   I recommend careful study of QST articles and the ARRL Antenna Handbook before wasting effort and money in this field.  73, bill

p.s.  Beware of crank designs on the internet including some that claim winding helical elements over plastic tubing are equivalent!



Until you build one; then you can qualify that statement. There is quite a following in the Yahoo Group and the designer is constantly building these things for Ham ops living in HOA's on the West Coast. They drive to pick up their antenna, rather than risk shipping costs and damage. A 72" loop gets pretty big.
Fred
Logged
KB4QAA
Member

Posts: 3064




Ignore
« Reply #7 on: December 01, 2013, 08:44:33 PM »

No qualifications needed.

1.  Anything that conducts electricity will radiate a signal.   Doesn't mean it performs as claimed.

2. Tom W8JI thoroughly debunked the 'helical wrapped small looped' supposed theory and claims.

3.  A Fool and his money....

4.  What do people's driving habits have to do with antenna design?  Smiley

best, bill.
« Last Edit: December 01, 2013, 08:52:24 PM by KB4QAA » Logged
KC4MOP
Member

Posts: 912




Ignore
« Reply #8 on: December 02, 2013, 03:45:33 AM »

No qualifications needed.

1.  Anything that conducts electricity will radiate a signal.   Doesn't mean it performs as claimed.

2. Tom W8JI thoroughly debunked the 'helical wrapped small looped' supposed theory and claims.

3.  A Fool and his money....

4.  What do people's driving habits have to do with antenna design?  Smiley

best, bill.
Rich, K8NDS, the designer is not making any claims that it outperforms standard antenna designs. It sometimes, like all antennas, will be the same or close to the performance of standard antenna design without the cost and weight of solid copper pipe, and could be tolerated in an HOA neighborhood. The helical design is not that popular, yet, but with the QRM noise of poorly maintained electrical systems in Europe and the price of land, a magnetic loop antenna is usually the antenna of choice.
So Tom, W8JI, makes a statement and the entire world stops. I read the back and forths on eHam when K8NDS introduced his design and I know Tom was in the fray with his theories.
Why does some different idea about an antenna get trashed, when the OP is looking for some guidance on a magnetic loop antenna? I gave a little testimony about what I built and a link to look at the design and consider building it. Once we get into the typical internet rants of "he says, they say"; then the entire idea of experimentation is down the tubes.

The OP wants to build something for 20M.
He can build the 33" diameter version of the Helical wound design and be on the air with a reasonable signal and QRO power.
Fred
Logged
KB4QAA
Member

Posts: 3064




Ignore
« Reply #9 on: December 02, 2013, 10:53:41 AM »

Again, I would strongly urge the OP to refer to the ARRL Antenna Book, and QST articles for sound engineering principles and proven small loop designs.  This will save you much time, money and grief.  bill
Logged
W4OP
Member

Posts: 635


WWW

Ignore
« Reply #10 on: December 03, 2013, 11:34:00 AM »

Has the designer of the helical magloop discussed (or is aware of ) current crowding on a flat conductor vs a tubular conductor?

Dale W4OP
Logged
KB4QAA
Member

Posts: 3064




Ignore
« Reply #11 on: December 03, 2013, 12:32:22 PM »

Yes, Current crowding was pointed out to him.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!