June 17, 2014

Small Transmitting Loops for Portable Use
 Featuring PY1AHD and his popular AlexLoop design!
 

Overview

What a special treat we have in store for the CWTD audience this time!  Alex PY1AHD, inventor and manufacturer of the immensely popular "AlexLoop" will be joining us for a discussion of Loop antennas for use while portable in the field.  This will be a very "practical" episode, where we briefly touch on STL design principles, and even describe a simple version that one can make with a some copper tubing and a capacitor. Many designs exist online for these narrow-band / highly selective antennas, and we'll point listeners to some of the popular homebrew approaches.

But the highlight of the show will be when Alex PY1AHD tells his stories of how he designed and evolved HIS version of the loop, appropriately called the AlexLoop.  The painstaking "cut-and-measure" techniques that Alex went through over time has produced an elegant solution for hams looking to take their ham radios along to the vacation house, while walking around on mountaintops, or even while sitting in the sand at a beach!

73, George N2APB & Joe N2CX

Listen to the Podcast

From the Chat Board ...

<20:12:51> "George N2APB": I hope everyone is following along with the material on our "whiteboard", located at http://www.cwtd.org/Jun_17-2014.html
<20:32:36> "Joe N2CX": Ray, K2ULR, interesting, eh?
<20:36:45> "Ray K2ULR": Yes! I notice "ratings" are good tonight. :)
<20:37:28> "Joe N2CX": You might chime in later with your experiences.
<20:37:38> "George N2APB": I was going to ask about the "secret sauce" ... gold!
<20:38:10> "Ray K2ULR": Sure.
<20:38:12> "Joe N2CX": Gold standard...
<20:43:29> "Alan W2AEW": I'd like to hear more about the considerations for the small driven coupling loop, and more ideas for design of the resonating capacitor (looks like this latter piece is Alex's secret sauce)
<20:44:32> "Rick K3IND": what is the radiation pattern of the loop? is it omnidirectional?
<20:45:09> "Joe N2CX": Radiation pattern for vertically-oriented loop is figure 8.
<20:50:29> "Alan W2AEW": wow, i didn't realize it was that critical - but certainly understandable
<20:50:45> "Joe N2CX": That is a gear reduction system to aid in tuning.
<20:55:17> "Joe N2CX": Too hot is not a problem here since center conductor is intentionally connected to shield!
<20:59:37> "Carlos PY1EGG": http://shakespeare-marine.com/new-gold-plated-adapters-and-connectors-offered
<21:00:57> "George N2APB": Thank you Carlos!
<21:01:29> "Carlos PY1EGG": You are welcome!
<21:08:42> "John - NG0R (Mac)": played with an STL
<21:21:41> "Terry WB4JFI": I've been playing with a couple of loop antennas from a local company here in Charleston, SC called Blue Collar Ants. I am using a 40M-20M and a 20M-10M. These handle up to 200W, or higher ...  http://www.bluecollarants.com/index.html
<21:28:28> "Carlos PY1EGG": Same with me, Joe!
<21:28:32> "George N2APB": Are they portable versions Terry?
<21:28:51> "Terry WB4JFI": Not really portable.
<21:28:51> "Ray K2ULR": Those Blue Collar loops look interesting... but I'm a QRP guy... :)
<21:29:32> "Terry WB4JFI": The most interesting part of them is the trombone capacitor design
<21:31:05> "Terry WB4JFI": The 20M-10M version is about 32 inches in diameter, but it is made of nonflexible copper.
<21:31:37> "Greg WB6DAI": TNX excellent program!
<21:31:47> "Terry WB4JFI": great program!
<21:32:02> "Carlos PY1EGG": See you all soon, 73.
<21:32:23> "Greg WB6DAI": 73, WB6DAI QRT
<21:36:32> "Ray K2ULR": 73 all dit dit

 

CWTD Episode #70:  Small Transmitting Loops for Portable Use

                                        ... Featuring PY1AHD and his popular AlexLoop design!

 

Topics:

1) The Basics

 

2) The AlexLoop!!

 

3) Quick & Easy Homebrewed Loop

 

 

 

1) Quick Review of the Basics:                                                                          And the Mag Loop "Facts of Life":

 

        

 

 

 

Equivalent Circuit                                      ... and ...                              Equations

    

 

 

 

The AA5TB Loop Calculator may be found at ... http://www.aa5tb.com/aa5tb_loop_v1.22a.xls

 

 

Editor's Note:  For a full treatise on this topic of Magnetic Loop Design
          ... be sure to check out a previous episode of CWTD (#21 from April 24, 2012), entitled "Magnetic Loop Cookbook" ... http://www.cwtd.org/Apr24.html

 

 

 

2)  The AlexLoop ... Featuring the designer: Alex PY1AHD

 

 

     

 

 

 

 

 

 

 

3)  A Simple Homebrew Design

 

   

            Project detail graciously provided by Alex PY1AHD.   See Alex's website for more very interesting and useful homebrew loop information ... http://www.alexloop.com/

Air conditioning soft copper tubes are perfect for loop construction. If you want to try a loop you must have an air variable capacitor or a vacuum variable capacitor.

The vacuum types are hard to find and expensive, but they have high isolation figures (ideal for high power operation) and can range from some Pico farads to hundreds of Pico farads indicated to design a small magnetic loop that can cover 10 meters to 80 meters.

For high power operation you will need big spacing between the plates of the air capacitor.

The most common variable capacitors present high losses due to the mechanical electric contact on the metal surfaces.

The most recommended are the butterfly or the split stator air variable capacitors.

Do not be disappointed with you have only the standard metal air capacitors. I still use them on some projects despite knowing all the performance compromise they can represent.

On the “Magnetic Loop Links”, you can have all the theoretical information to design your loop. My personal proposal is give to the reader practical ideas for the loop construction.

On the following photos can be seen two soft copper small magnetic loops, both of them are made on 3/4 inches soft copper tubes.

The bigger has 91 CMS in diameter and measures 2.89 CMS from each extreme.

The excited loop is made on coaxial cable and measures 2.89 CMS divided by 5.

The capacitor is 10 Pico farads to 80 Pico farads split stator.

The smaller one has 66 CMS in diameter and measures 2.08 CMS from each extreme, and is closed with a standard 12 to 100 Pico farads capacitor.

The excited loop follows the 1/5 of the main loop measures.

 

 

 

REFERENCES


AlexLoop ... http://www.alexloop.com/

    Alex Grimberg, PY1AHD sells several varieties of small transmitting loops that can be quite handy for portable or hand-portable use. 
    He describes a number of different configurations he has designed and some videos of the loops in use on the air.

 

Loop Analysis Calculators:

1) aa5tb_loop_v1.22a.xls calculator
    Good overall calculator.  Does not account for ground loss, handles only round loops – works with OpenOffice as well as MS Excel ...  http://www.aa5tb.com/aa5tb_loop_v1.22a.xls

2) KI6GD calculator
    More general than the AA5TB calculator ... http://www.magneticloopantenna.com/loopcalc.zip

3) G4FGQ Calculators
    Numerous DOS calculator programs including several for small loops.  Handles many more parameters than above calculators, though we have not verified accuracy ... http://www.zerobeat.net/G4FGQ/page3.html

 

Loop Designs and Products:

1)  Steve Yates AA5TB site ... http://www.aa5tb.com/loop.html

    One of the best overall reference sites on the Web \describing the theory and practice of small transmitting loop antennas.  Has additional links to other sites.

 

2) KI6GD site ... http://www.magneticloopantenna.com/

    Yet another good site for the serious loop fan.  Also has other links.

 

3) W2BRI site ... http://www.standpipe.com/w2bri/

    Excellent site for low HF band very efficient transmitting loops, including a 12’ x 12’ square loop for 80 meters

 

4) MFJ site ... www.mjfenterprises.com 

    MFJ sells some pretty good HF loops, pricey, but good

 

5) G4TPH site ... http://www.g4tph.com/

Tom Brockman sells several unique small transmitting loops which break down into small sections for easy transport and setup for temporary installations.

 

6) An Auto-Tuned Mag-Loop Antenna, by AA0VE ... http://www.4sqrp.com/4sqrpNewsLetter/201406.pdf

 

7) The Midnight Loop, by N2CX & N2APB ... http://www.midnightdesignsolutions.com/MidnightLoop/Midnight%20Loop%20(Mar%2011a).pdf

 

Other Small HF Loop Sites (list from http://www.aa5tb.com/loop.html ) 

 

 

 

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