Isn't she beautifull...

Article (pdf) about me in a local newspaper (Leyebode nov. 2009) --> 

 

 

My Versa tower behind the house with a trapped Inverted-V,
a 5el 2-bander for 20 and 15 meter.
Each band has its own full-size radiator with gamma-match.
With a coax-relais I can choose remotely which band I want to use.
Further a fixed 70cm yagi and on top a 70/144 vertical.

 

 

My "Magnetic Loop" project. (Started in dec 2008)

Many hams are using a "magnetic loop" antenna. So I got curious and started collecting information about this antenna. The Internet is a great source.

After some calculations with "loopcalculator.xls" I decided to go for a 1.8 - 7 Mc loop capable to run 100 Watts. A loop with a diameter of 400 cm is the goal.
The Loopcalculator showed me I needed a vacuum variable capacitor of 25-600 pF/5KV.
On Ebay I found my cap...  15/750 pF - 5KV

15 meter, 22mm copper tubing was ordered...  

 

Januari 2009...

I want the copper tube to be a perfect loop so I made a simple tool:



Then I started with the motordrive, 4mm spindle to control the slide-potmeter and the end-switches.
febr-mrt 2009...

Lucky I have a metal lathe.. 

may 2009....
 
Here some pictures of the whole assembly. As isolator (and for alignment) I used a piece of rubber tubing.
(See the clamp on the rubber tubing to hold it on the drive-shaft. The rubber tubing fits tightly on the cap so
I don't need a clamp and it works like a frixie link in case the end-stop micro-switches mal function.
 

Looks good doesn't it!
 
 
All copper pieces are put together by brazing.
The green plate I used is Trespa (a strong kind of Pertinax), 8 mm thick.
 
 
All bolts, nuts and washers are Inox.
I need 4 wires for control of this unit. 2 for the DC-motor (turning left or right) and 2 for the potmeter.
 
Next thing to do is bending (rolling) the 22mm copper pipe and the cap-unit enclosure is to be made.
 
to be continued...... PA0KV
 
 
May 10, 2009
 
Bending the copper tube.
The intention was to push the tube between the three wheels and adjust the middle wheel bit by bit
to reach the radius I wanted. But the copper tube did not want to be pushed around. So I had to change
the bending tool. I added a little swing handle.
First I drew a half circle with a 4 meter radius on the ground. Some crepe tape made the pencil drawing
more visible. 
 
 
The bending tool had to be mounted high enough...
 
 
See the little handle on the middle wheel.
 
 
 
 
 
Checking the radius...
...... looking good. :-)
 
The completed loop with the vacuum cap..
 
 
 
How do you mount a 4 meter loop vertical? I choose for a Y-joint and some 36mm surplus epoxy tubing
(military tent sticks) which are 120 cm long and can be stacked together. I glued them with two-component
polyester.
 
 
 
The whole assembly....
 
 
 
 
 
Gamma maching.......
 
 
SWR 1.1 on 80 meter
 
 
SWR 1.1 on 160 meter.
 
 
Finished you think?
 
Well, not quite. The weight of the vacuum cap with mounting plate, motor drive, etc. was too much for this Y-construction.
The cap-assembly + enclosure needed support. So I decided to go for a +-construction......
 
to be continued...... PA0KV
 

 

Busy day today... may 29, 2009.....

Creating the +-joint was easy using a piece of Trespa and bending some aluminum strip. The white stuff in
the middle of the epoxy tubing is glue.

 

Here is the assembly....

 

The vacuum cap has to be 'all weather proof' ...  here the 160 mm PVC enclosure with glued PVC support
to fit on the epoxy tube.

 

The wires for cap-motor and slide-potmeter are lead through the vertical tube of the +-joint. In some way this
feels better than leading them through the copper loop.
I can't get it out of my mind that leading the wires through the copper loop has some bad influence on the loop's
performance.

Another thing was keeping my mind busy. How to mount the cap-assembly into its enclosure without drilling
holes in it? Holes would make it less 'all weather proof'.
Well, after another cup of coffee and some serious 'number-crunching' I came up with this....
  

to be continued.....

 

11 june 2009 ..

This is the idea... turning the cable-tensioner will push the doorstop upwards and the base-plate downwards.

 

..and the other side..

 

Something wrong in the pictures?.......

Yes, the cap-assembly is upside-down. It was just for the pictures.

Okay, let's put it up...

 

 

Two high-tech equipment in one picture....

Final position...

 

Grounding a Magnetic Loop..... 5 meters copper pipe pushed (by water) in the ground.

Loop and shield of steering cable are grounded.

 

View from the shack...... june 13, 2009. 

Now I'm testing it... first rapports from PA-land on 80 and 160 where very good.

Mei 2013.
Designed with the loop-calculators on the web it should tune on 160, 80 and 40M.
But in practice the Loop has to be a little bit smaller in diameter to tune it on 40M.
Too much L in the circuit in this setup.

Bandwidth.
On 80M, tuned 1:1 with the vacuum cap, bandwidth is +/- 5.5 kc, swr 1.5:1
on 160M,   ""                                                  ""          +/- 1.1 kc, swr 1.5:1

The vacuum cap is a 5KV type so 100 watts is save.
In compare with my Inv-V on 80m there is little or no difference in send and received reports.
(Local European contacts.)
But the Loop is much more quiet and no splatter from nearby stations.

73's, Twan - PA0KV