[Antennas] Re: ...#14 wire is about 740 kHz wide

[Terry Conboy]

At 11:45 AM 2004-08-06, DavidE Benedict wrote:
>Terry, this doesn't seem right ... but 740Khz seems pretty wide for this 
>wire at 17m...

In EZNEC, I just made simple model of a #14 straight copper wire with the 
bottom at 20 feet above "high-accuracy" average ground and the top at 46.29 
feet.  It's resonant at 18.118 MHz with a feed Z of 72.35 ohms.

Here's the impedance and SWR data:
"EZNEC ver. 3.0"
"Vertical Dipole 17m","2004-08-06 2:18:24 PM"
"Alt Z0: ",75
"Freq MHz","Src #","R","X","SWR (50 ohms)","SWR (alt. Z0)"
17.75,   1,  67.75967,  -29.86191,   1.801077,  1.533817
17.8,    1,  68.36962,  -25.78629,   1.707608,  1.447311
17.85,   1,  68.98463,  -21.71991,   1.626413,  1.366237
17.9,    1,  69.59151,  -17.63852,   1.557783,  1.290047
17.95,   1,  70.21621,  -13.56911,   1.50393,   1.218888
18,      1,  70.84589,   -9.500603,  1.466052,  1.152727
18.05,   1,  71.47975,   -5.446606,  1.445677,  1.092582
18.1,    1,  72.11919,   -1.375957,  1.443394,  1.044363
18.15,   1,  72.76368,    2.683161,  1.459014,  1.048414
18.2,    1,  73.41312,    6.756164,  1.491153,  1.098004
18.25,   1,  74.0561,    10.80636,   1.537356,  1.15653
18.3,    1,  74.71566,   14.86495,   1.596164,  1.219313
18.35,   1,  75.38007,   18.91906,   1.665427,  1.285321
18.4,    1,  76.04944,   22.97178,   1.743762,  1.354351
18.45,   1,  76.72517,   27.03779,   1.830418,  1.426582
18.5,    1,  77.40441,   31.08219,   1.923891,  1.501341

The last column is the 75 ohm SWR, and as you can see, it's just over 1.5 
at 17.75 MHz and 18.5 MHz.  Inside the 17m band, it's under 1.1:1.

The bandwidth and impedance will change somewhat, both up and down, as you 
vary the height of the antenna.

There's a free demo version of EZNEC 4.0 (limited to 20 segments) available 
at http://www.eznec.com that will work fine for this antenna, if you want 
to try it yourself.  I'll send you a copy of my model description, if you like.

NEC2, which is the basis for EZNEC, should be very accurate for antennas 
like this.

73,
Terry N6RY