same antenna I purchased. I bought the Cobra junior antenna and
followed the directions for installation. The antenna is 50ft in the
air in a flat top configuration. When I hooked it up to my radio, it
would not tune on segments of certain bands, most noticeably 75/80. I

That all seems pretty reasonable though the explanation that the
"built in tuner would not accept more than a certain level of SWR" is
not a good way to express the limits of internal tuners, but it is an
explanation that would appeal to those with lesser knowledge.

The problem is that antenna is advertised to work all bands.
Unfortunately it doesn't do very well on many bands.

The SWR is "off the scale" on many bands.

The same would be true of almost any other doublet-style antenna, I
think. Such antennas are often usable on a large number of bands if
you have a wide-range transmatch/tuner, but I don't think I know of
any which are usable in this way with the limited-matching-range
"line flattener" ATUs built into modern solid-state transceivers.

The Cobra Ultralight is only about 60% as long as a normal resonant
near-half-wave dipole for 75/80 meters. It's shortened by linear
loading. I imagine it has a narrower SWR bandwidth than a simple
dipole.

The manufacturer states that a tuner _is_ required. The wording is
perhaps somewhat more optimistic about using a transceiver's built-in
ATU than is justified, though. I wouldn't plan to use an antenna of
this sort without a good external tuner with balanced-output
capability (whether intrinsic or via a good current balun).

The original poster might want to consider making a multi-wire (or
"fan") dipole. With several sets of wires it'd surely be possible
to make one which would tune on 80, 75, 40, and 20 well enough to not
need an external tuner... although fitting it into under 80 feet of
linear space might prove to be a challenge.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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