Ham Radio

Sunday, January 24, 2010
Trans Match System For Loop Antenna's
I have been using my home made Delta Loop vertically polarized for the past couple of years with very good results. The Delta loop was made by myself with the intention of using it on 20M, I originally blogged about it here and since then, It has moved from the horizontal to like I said already a vertical configuration.

The horizontal testing of the loop brought slight noise levels where as the vertical triangle or pyramid configuration, is very quiet for noise and excellent on performance both RX and TX. The only issue I have had with the Delta loop was with my original calculations which proved to be slightly long, making it resonant on 13MHz instead of the desired 14.200 frequency. I cut the loop around two years ago and unfortunately made it too short as it was now resonant at 14.800 which was slightly higher than the intended frequency.

Subsequently I have been managing fine with the help of the ATU, but the burning feeling inside has been growing and niggling away as I have wanted the antenna to be perfectly resonant across 20M without any tuning. I had been chewing over various ideas that I have had and rather than replace the complete length I decided I had had enough guessing and needed to come up with some way of an easy adjustable matching system.

I thought about complicated tuning systems but in the end settled for some 3.2mm TIG welding wire, which I formed into a neat loop type hook on one end which connects to the dipole centre replacing the wire.I then slid the original wire up and down the 3.2mm TIG wire and secured the end with a terminal block as seen in the image.
Once I adjusted the overall length I got the SWR down to 1:1 /1:5 across the 20M band. I then fired up my plumbing blow torch and soldered the original delta loop wire to the added 3.2mm tig wire ensuring a excellent connection which would be permanent and WX proof.

The next image shows the feed point of the loop (dipole centre) with 3mm electrical wire (70ft long on Right hand side) and 3.2mm TIG wire (2ft long coming out of the Left hand side).
This image shows the movable trans matching system which once adjusted was soldered up outside to finish off the modification.
Hope this idea will be of use to some of you that are struggling tuning up any loop antennas. Now its time to try it out ATU free and see who is on the band.
posted by Simon Davison @ 4:13 pm  
2 Comments:
  • At 11:08 am, Blogger Atul Vhale said…

    This comment has been removed by the author.

     
  • At 12:13 pm, Blogger Brent said…

    A system particularly useful for feeding antennas employing one electrical wavelength closed loop driven elements. Single or dual wire transmission line sections provide impedance match between the high voltage, high impedance feed point on the loop and a low impedance antenna feed line. Selectable polarization with high isolation between feed lines is provided by the connection of a second transmission line section to a point located 90 electrical degrees away on the loop, at the current maximum when the other feed point is excited.
    Ham Radio Accessories

     
Post a Comment
<< Home
 
Custom Search



 
About Me

Name: Simon Davison
Home:
About Me:
See my complete profile
Previous Post
Archives
Links
Powered by


free counters
>
BLOGGER