[TowerTalk] 80M antenna wire size

[jimlux]

On 1/5/20 9:57 AM, Jim Thomson wrote:
> Date: Sat, 4 Jan 2020 14:37:10 -0700
> From: David Gilbert <xdavid at cis-broadband.com>
> To: towertalk at 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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