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coaxial dipole
I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth is
....[snip].... has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia = 8")... I'm curious why a 2-foot-square cage has an effective diameter of only 8" If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500 & 4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses (24"x24"). I use #14ga 168-strand soft-drawn copper wire .... Doesn't soft-drawn copper stretch like mad? -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license |
#2
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coaxial dipole
Myron wrote:
I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth is ....[snip].... has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia = 8")... I'm curious why a 2-foot-square cage has an effective diameter of only 8" It's apparent to me that it can't appear that large because it's 4 strands of 14ga wire instead of a 24" diameter cylinder. I obtained the 8" figure from the calculator program at: http://www.smeter.net/antennas/dipcage2.php. I don't know how the effective diameter was calculated. If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500 & 4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses (24"x24"). I use #14ga 168-strand soft-drawn copper wire .... Doesn't soft-drawn copper stretch like mad? I was told by the CSR at Davis RF that it's soft-drawn but I expect it's hard-drawn -- an unscientific stretch test in my workshop appears to confirm this. Over a 12 month period, a 12ga single-wire 80m dipole (with choke balun & RG58 feedline) did not noticeably stretch. Also consider that in my case, the cage dipole is in inverted vee form, so there's no concern about wire stretch caused by the heavier LMR400 feedline & balun weight. Also, it's 4 strands of 14ga wire instead of one, and the spreaders don't add much weight. -- --Myron A. Calhoun. Bryan WA7PRC |
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