[Boatanchors] Good (And Bad) Lengths For End-Fed And Dipole Antennas

Mon Nov 23 23:58:17 EST 2020

For anyone wanting to read less:- Those numbers are in feet.- Numbers were optimized for band centers.
- 'Random Wire' means NO feed line, just a length attached to your TX or Tuner & run out to some handy support at the other end. Often 'Random Wire' is used instead to mean some arbitrary length of wire that you happen to have on hand or that you happen to have room to stretch out & in that context the term may include various feedline stratagems to transform impedances.
Nice work & clever layouts for the data.
WayneWB4OGM

-----Original Message-----
From: D C _Mac_ Macdonald <k2gkk at hotmail.com>
To: boatanchors at mailman.qth.net <boatanchors at mailman.qth.net>
Sent: Mon, Nov 23, 2020 6:33 pm
Subject: [Boatanchors] Good (And Bad) Lengths For End-Fed And Dipole Antennas

Back in 2013, Jack, VE3EED (SK) published a scientific
analysis of good and bad lengths of antennas regarding
ease of matching.  Basically, any length of wire that was
a multiple of 1/2 wavelength would present an extremely
high impedance (high voltage point) that will be very hard
to match to any transmitter OR trans-match.

Jack did a mathematical exercise to select the bad AND good
lengths to use.  These lengths to use or avoid are shown below.
These are BAD lengths for simple "random-wire" end-fed
antennas and are the same for the sides of half-wave dipoles
that are going to be used for multi-band operation.

BAD:

16  19  22  26  32  33  38  44  46  48  52  64  65 66  76  78

80  88  92  95  96  99  104  110  112  114  123  128  130 132

133  138  144  152  154  156  160  165  171  176  182  184

190  192  195  198  208  209  224  228  230  231  234  240

242  246  247  256  260  264  266  272  276  285  286  288

297  304  308  312  320  322  323  325  330  336  338  342

352  361  363  364  366  368  369  374  380  384  390  396

399  400  414  416  418  429  432  437  440  442  448  455

456  460  462  464  468  475  480  484  494  495  496

Some of these numbers are too close to squeeze in

between them.

Here are the final numbers (in my opinion) in green below

that would be good for a long-wire antenna: (You may want

to make a note of them)

29  35.5  41  58  71  84  107  119  148  203  347  407  423

These are for the center frequencies of all bands from 160
though 10 meters and cover antenna (and half dipole)
lengths out to 500 feet.

Mike, AB3AP, favors CW so he wrote a program to calculate
this stuff for the lower edge of the CW bands.

If this is more your own cup of tea, you might wish to check

http://udel.edu/~mm/ham/randomWire/<https://nam12.safelinks.protection.outlook.com/?url=http:%2F%2Fudel.edu%2F~mm%2Fham%2FrandomWire%2F&data=04%7C01%7C%7C28e1179c657d4ed9627c08d890069cf1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637417705356267642%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=OcJhukhGkoKOVwl7mnJWZtXeUam4xa5CSgVlTOk%2FTio%3D&reserved=0>

Note that Jack, VE3EED, went SK several years ago...he will be missed.

(Also check out AB3AP'S website<https://nam12.safelinks.protection.outlook.com/?url=http:%2F%2Fudel.edu%2F~mm%2Fham%2F&data=04%7C01%7C%7C28e1179c657d4ed9627c08d890069cf1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637417705356277638%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=KNX75z8la4iIWMo%2FpmbWo%2F%2BD5X1ACwNTIGiy2jX%2BaJE%3D&reserved=0> and say thanks for sharing his skills.

They just saved you and me loads of time and frustration.

N4UJW

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