On 1/5/20 9:57 AM, Jim Thomson wrote:
Date: Sat, 4 Jan 2020 14:37:10 -0700
From: David Gilbert <xdavid@cis-broadband.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 80M antenna wire size
<According to EZNEC+, an 80m dipole at 100 feet (resonant and matched at
<3.7 MHz) has a 2:1 SWR bandwidth from 3.55 MHz to 3.87 MHz with #10
<copper wire and from 3.57 MHz to 3.86 MHz with #18 copper wire. Much
<thicker conductors or similar conductors at higher frequencies would
<make more difference of course (I've modeled 12 inch diameter wire cages
<for 80m and they make a usable improvement in bandwidth), but in spite
<of what somebody just posted the advantage for #10 wire on 80m does not
<seem significant to me for bandwidth.
<Dave?? AB7E
## 10 gauge wire is .102 inches in diameter.
18 gauge wire is .0403 inches in diameter.
## .102 / .0403 = 2.531
## 10 gauge is 2.531 x the circumference of 18 gauge wire. Thats a
bunch.
Thats a huge difference in Length to diameter ratio.
## I have never tried a 80m wire dipole at 100 ft, but have
used a full sized wire inverted vee on 80m.
## 10 gauge wire provided for a much wider BW, vs the 16 +18
gauge I tried previously.
2 other folks here in town tried the same experiment...with same
results. Again, inverted vee used.
Is EZNEC modeling your dipole correctly ?
The effect on bandwidth of l/d get smaller as l/d gets bigger. So a
change from, say, 100 (10 meters length, 10 cm cage diameter) to 1000
(10 meters, 1 cm) is a lot bigger than the change from 1000 to 10,000.
l/d for 80 m (l = 40 meters)
40/0.0026 = 15,384
40/0.001 = 40,000
15,000 is huge for l/d, there's not much difference when you go to 40,000.
Jim VE7RF
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