wrote in message
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Rockinghorse Winner wrote:
I was checking the lengths for a 15 M dipole up 18 feet and the EZNEC
calculated length was about 10% longer than using 468/F. I was wondering
if
the EZNEC calculation takes other factors into consideration and what
these
may be? Thanks alot.




CUL8R



R*Horse





"Take a look behind you - upstream - now you begin to
recognize this country, don't you?"

"Yes, I do recognize it now. It is the most wonderful
thing I ever heard of; by a long shot the most
wonderful - and unexpected."

Mark Twain
Life on the Mississippi



http://rwinner.blogspot.com
Hi RH, The proximity to ground, the ground type, and the length will
be the factors that determine the source impedance of the dipole. I
just ran a dipole cut for 21.3 Mhz by the formula, 18' up over real
ground and found it to be off by 3%. Moved it up to 36' and it was off
by 1%. Your 10% sounds a bit high. The conductor size of a wire
dipole will have some effect at 15m, but I did not try anything
different than #12 wire.
Gary N4AST

Just to be different, I tried #18 wire. Using 468/f gives a length of 21.9
feet at 21.3 MHz. According to EZneck, this is resonant at about 22 MHz. A
length of 22.4 feet gave resonance at just a shade above 21.3 MHz. Making
the wire 10% long put the resonance below 21 MHz. All at 18 feet.

I ran SWR from 21 to 22 MHz, with a step size of .05. Number of segments was
19.

Tam/WB2TT