[TowerTalk] Suggestions for 80, 160m?

[Bill Coleman AA4LR]

On 5/11/00 5:30 PM, Jonathan Kaplan at jonk@jskent.com wrote:

>	I'm think of putting up an antenna to cover 80 and 160 m bands and
>I find all the argument about low band antennas somewhat confusing, so I'll
>just ask straight out: What kind of antenna will give me DX on low bands?

Most DX transmitting antennas for the low bands, when used with (relative 
to the wavelength) short supports are verticals. Horizontal antennas, low 
to the ground aren't that effective. (Although I did work TM2Y on 80m 
with a 15 foot high 80m dipole and 90 watts....)

>	I have a 55 foot tower (crank-up) on a hilltop near the ocean
>  with a 40m rotatable dipole and a TH7DX on the top.
>There is a 20 foot pole available about 100ft away downhill, available for a
>sloper if needed and it probably would be difficult to bury radials.
>	Given  all that, what kind of antenna would work best?\

Why would it be difficult to buy radials? 

I'm planning a similar installation, with a 49.5 foot bracketed tower, an 
A3S with a 40m kit. For 80m, I plan to shunt feed the tower, using a 
gamma or omega match. With the beam acting as a capacity hat, it should 
be close to a proper quarter wavelength vertical. For 160m, I haven't 
decided yet. Seems like the tower is much too short to be an effective 
radiator for 160m. (like less than .1 wavelength)

An alternative would be an inverted L. These work well. You could slope 
an inverted L for 160m down toward your pole 100 feet away with good 
effect.

The key to either shunt feeding or an inverted L is an effective radial 
system. With the shunt feed, you just about have to use ground radials. I 
plan on as many and as long as I can fit in my lot. If you elevate the 
feedpoint of the L, you can use elevated radials. The supposed advantage 
of elevated radials is that you don't need as many to make an effective 
radial system. (This is a matter of some debate -- there are a lot of 
success stories, but the field strength measurements comparing a proper 
ground radial system with an elevated system don't match) The 
disadvantage of elevated radials are that a) you lose some of the 
effective hieght of your support and b) you have to find a way to support 
the radials. 




Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
Quote: "Boot, you transistorized tormentor! Boot!"
            -- Archibald Asparagus, VeggieTales


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