If this is to be a traditional vertical, it should have a base insulator. If
not a slant wire shunt feed is possible. There is no magical number for
height. In practice an 80M vertical could be anywhere from 35 feet or less
to over 140 feet. It is the matching that counts. The scientific way would
be to either model or measure the resistance and reactance and then match
that to 50 ohms. The taper has little or nothing to do with your results in
this case. Depending on how much you want to spend, either use and outdoor
antenna tuner at the feed point or run mismatched coax to the shack and use
an indoor tuner. If you are only interested in 3510 kHz, build a fixed
matching network at the mast and it will be the same as 1000s of broadcast
stations. The most important point is to have the best ground system
possible. This should be anywhere from a minimum of 4 buried radials at
least 1/4 wavelength long up to 120 radials. The more the better, it depends
on your space and wallet. QST and QEX have numerous articles on ground
systems.
On 9/4/09 7:28 PM, "Carl" <aa4h@charter.net> wrote:
> I am trying to build a vertical for 80 meter CW. I purchased a 65 foot
> telescoping aluminum tubing kit from DX Engineering model DXE-ATK65
> thinking this would be a way to get a quick and cheap vertical going.
> Has anyone tried this? The instructions show the assembled vertical as
> being 65 feet. This appears to be too short for a frequency of 3510 khz.
> The telescoping diameters vary from 2 1/8 inches down to 7/8 inches in 6
> foot lengths with overlaps to make the entire length 65 feet. Is it
> necessary to take the taper schedule into account when trying to decide
> the correct length? Yagi designers fret over taper schedules and also
> mounting hardware so am I going to need to also? I'm of course trying to
> minimize the amount of trial and error tuning with something this tall,
> just standing it up once seems like enough. Thanks for any comments.
>
> Carl AA4H
>
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