Jim VE7RF wrote:
>>> The F12 N style 40m eles are not full size. They range from 59 ft for the
>>> REF...down to aprx 52 ft for the DIR.
Well, now we're making some progress at reaching common ground. I created a
dipole model with 1.5" diameter aluminum wires and adjusted the length for
precise resonance at 7.15 MHz in free space. Then I changed the length to 85%
of the self-resonant length, added loading coils mid-way out each leg, and
adjusted the coil inductance to again get precise resonance at 7.15 MHz. And
finally I changed the length to 70% of the self-resonant length and again
adjusted the coil inductance to get precise resonance at 7.15 MHz. Coil Q was
kept constant at 200.
Then I switched from free space to average ground and varied the height of each
dipole from 10 ft to 100 ft, this time adjusting the *frequency* for precise
resonance at each height while keeping the length and coil inductance (if any)
constant.
http://s33.postimg.org/v51yi2n5b/resonate6.png
100% length (69.79 ft), no loading, +218 KHz change from 30 ft to 60 ft.
85% length (55.93 ft), 3.297 uH coils, +137 KHz change from 30 ft to 60 ft.
70% length (46.06 ft), 6.721 uH coils, +78 KHz change from 30 ft to 60 ft.
So it seems that more loading results in less change in resonant frequency as
the height above ground is varied.
Dan, AC6LA
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|
