5
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W8OFC    
Marana, Arizona


 

 

 

 

   ANTENNAS - Page 1 of 3
 
The pages in this section of the website will feature some of my favorite antennas as well as current antenna projects.
 
   SMALL 3' DIA. LOOP ANTENNA -
   20 THRU 10 METERS
 
This is an amazing (and, I think, under-rated) little antenna !  No, it will not outperform a 3 element beam, it will not necessarily out-perform a dipole (but, in some situations, it does!); and, if made correctly, requires more work than assembling a wire dipole.

On the other hand, it performs very well sitting right on the ground (great for those living in a CC and R restricted neighborhood), does not require radials, is extremely quiet when receiving, and all materials except the variable capacitor and the coax connector can be obtained from Home Depot, Lowes, or possibly, your local hardware store.

 


The main part of the antenna was constructed of (8) 14.125" sections of .75" copper pipe and (7) 45 degree elbows to form an approximate 3' diameter loop.  (OK - so it's actually an octagon.)  A small loop antenna like this has an extremely low radiation resistance; around .1 ohm.  So it is apparent that the introduction of any resistance, even only .5 ohm, would substantially reduce the efficiency.  Because of this, it was essential that I sweat-solder all of the joints together.  (Don't look too close.  I'm an electronics guy - not a plumber!)

 


A series-wired split-stator capacitor (found at a hamfest for $2) was used so that there is no wiper contact resistance in the circuit.  The use of this type of capacitor is the primary reason for small loops which work great versus those which do not.  The capacitor was attached to the loop with copper straps which were initially bolted to the loop to hold them in place while soldering the other ends to the capacitor.  The bolted ends were then soldered to the copper pipe.

 


The antenna can be fed several ways.  One method is to solder the shield and the center conductor of the coax directly to the loop at a distance apart determined by trial and error.  (I believe this is called shunt feeding).

As you can see in the picture, I choose to go with loop coupling, so I flattened the bottom of the loop to install a coax chassis mount which also serves as the attachment point for a small copper wire coupling loop.

 

I AM AWARE THAT I DID NOT INCLUDE ALL OF THE SPECIFIC DETAILS ABOUT THIS ANTENNA.  IF YOU WOULD LIKE TO BUILD ONE, SEND ME AN EMAIL BY CLICKING ON THE BOX BELOW, AND I WILL SEND YOU THE REST OF THE DETAILS AND TRY TO ANSWER ANY QUESTIONS YOU MIGHT HAVE ABOUT THE ANTENNA.
 
   NEW ANTENNA ON PAGE 2
 
The antenna that I've been working on (prototype version) is finally done and I'm really quite surprised and pleased about how it performs.  Click on the box below to go to Page 2 to check it out.

 
 

 

PAGE 2

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