[TowerTalk] Antenna design questions please
RadioIR at charter.net
Wed Nov 30 23:05:10 EST 2005
Here is a quick simulation. This may not be exactly what you are
thinking because I don't know how high the ends of your vee will be off
the ground, but it should give you an idea of what to expect. I assumed
the ends were at 15 ft, and set the antenna for resonance at 1.8 MHz
(resonance at the antenna, not at the end of the feedline). With 65 ft
of 600 ohm line, and a 4 to 1 balun, the SWR at the switch box would be:
1.8MHz = 24.7, 3.6 MHz = 3.5, 7MHz = 7.9, 10.1MHz = 12.2, 14MHz = 4.5,
18.1MHz = 5, 21MHz = 3.3, 24.9MHz = 9.2, 28.1MHz = 9.6. Probably not
what you are looking for.
There is a basic problem with trying match a 160M inv vee to get a
reasonable SWR on 80M. On 80 meters it is very high impedance. One
solution would be to use the feedline as a tuner. This would require
that you switch feedline lengths for each band. For example for this
antenna, you would need 260 ft of 600 ohm feedline for 1.8 MHz and 200
ft for 3.5 MHz. This can become a real switching nightmare for more than
about 2 bands. You would not need the 4 to 1 balun, but you would need a
good common mode choke balun at the end of the feedline. If you are
interested in this approach see:
You can also use 450 ohm ladder line instead of the 600 ohm line, but
the required lengths will be a little different.
Probably a simpler approach is to convert your inv vee into a fan
dipole, with an element for 160M and another for 80M.
Gary.Stone at med.va.gov wrote:
>I am thinking of putting up an antenna and would like your input please? I
>am thinking of putting up an inverted vee configuration and then feed it
>with 600 ladder line so that it would be tunable on 160 thru 10 meters. I
>am thinking the apex would be at about 70 feet on the tower and the two legs
>would be about long enough to allow tuning for 160 meters (about 120 feet or
>even a little more on each leg). I would like to take the 600 ohm feedline
>down to the rat pak (PL259) switch box on the tower - mounted at about 5
>feet up from the ground. So, it would have about 65 feet of 600 ohm ladder
>line. From my rat pak to the shack is 50 ohm LMR400. I would also consider
>using twin lead (easy to buy in rural North Texas) but also want to run 600
>watt amp if desired. I am thinking I would need to use a 4-1 balun at the
>bottom end of the ladder line and then connect a short coax jumper to the
>I now have an alpha delta sloper (DX-A) with the apex at about 60 feet. I
>am hoping to improve my signal on 80 and 160 with the added plus of being
>able to load up easily on other bands (hence the ladder line feed line).
>Ideas? And how far do I need to put the feedline away from the tower - is a
>couple feet ok? Thanks in advance for any tips and critique.
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>TowerTalk mailing list
>TowerTalk at contesting.com
More information about the TowerTalk