[TowerTalk] TowerTalk Digest, Vol 259, Issue 15 160 meter trap/coil

[john simmons]

I follow this and all antenna discussions with passionate interest.

Three questions:

  *   Where might I find a drawing of the 630m antenna?
  *   In what issues of QEX were the mobile antenna articles published?
  *   "...limitations of NEC related to this work is that it doesn't model current distribution in antennas with loading coils very well" Does this include NEC-5?

73
-de "Curly" John NI0K
QRZ.com<https://www.qrz.com/db/ni0k>
Hamshack Hotline<https://hamshackhotline.com/> call me: 6100271

On 7/24/2024 3:26 PM, Jim Brown wrote:
Right on all counts. But I have a related observation, which is best seen in an NEC model that is used to either study someone else's design, to potentially modify it to fit on one's own real estate, or to design from scratch.

The design that made it jump out for me was one of two antennas designed by the VK who was one end of several 630M distance records several years ago. Neighbor W6GJB was very interested, and wanted to rig something.

The design that we worked with went straight up for some practical height, ran horizontally at that height, then dropped down to just above ground and then ran horizontally for a long distance. There was no lumped loading. All of those dimensions were tweaked so that the primary current maxima was in the downward vertical run. The feedpoint Z was high, and as anyone with AM broadcast design experience knows, ground losses fall fairly fast with decreasing frequency, so no radials were needed. It's a brilliant design.

The tweaks that I did were 1) to work with the heights that were practical with Glen's redwoods, 2) to split the long end run into two shorter runs that could fit on his property; and 3) a simple, low loss matching network at the feedpoint.

Glen had great success with that antenna, including working the guy in VK several times.

The great work on loading for mobile whips published in QEX is well worth extensive study. It's in two parts that cover the theoretical concepts, verification of measurement techniques, and a lot of measurements of various positions of the loading coil.

One of the major limitations of NEC related to this work is that it doesn't model current distribution in antennas with loading coils very well.

73, Jim K9YC