On 8 Jun 2006 05:42:37 -0700, wrote:

Buyer Beware

Hmmm.

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
called Joe to get some help and was told that my radio, which has a
built in tuner would not accept more than a certain level of SWR and
was told to trim the twinlead back 19 feet. I did and while some of the
problem was solved, I continued to have problems on 75/80. I emailed
Joe to ask for further assistance and was told that the next step was
to buy a tuner extender (price $60). Not the answer I wanted to hear.
If in fact this kind of problem exists with radios that have built in
tuners, prospective buyers should know that in advance. For the cost of
the antenna and now the tuner extender, I could have bought a better
antenna, which is what I intend to do. I am not pleased with this
antenna and would not recommend it especially to someone who has a
radio with a built in tuner and intends to use it. Additionaly, the
performance on 40 seems to be very good. It seems to under perform on
20. Can't tell on 75/80 because I can't tune the band.

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.

Well, it looks like you have learned something that many of us know,
that the internal tuner in most radios has quite limited range and is
really for minor trimming of loads to enable the radio to develop
rated power (not to mention poor efficiency on the lowest bands).

Joe advertises honestly that the antenna will need a tuner for
operation on any frequency, perhaps he needs to spell out that what
manufacturers fit into a corner of a transceiver may not be up to the
task.

Frankly, I am wondering why your beef isn't equally with the
transceiver manufacturer for deceiving you with a tuner that isn't up
to the task.

I wonder what "better antenna" you have in mind? The short multiband
HF antenna that has low SWR(50) on all bands (since you have an issue
with tuners) and good performance is the holy grail of HF amateurs
that will provide you with challenge for the years ahead.

To some extent, the residual technical content in amateur radio is
mating up system components that are compatible to form a working
station.

Owen
--

Owen Duffy wrote:
On 8 Jun 2006 05:42:37 -0700, wrote:

Buyer Beware

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.

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

Sounds like a G5RV.
--
73, Cecil http://www.qsl.net/w5dxp

My trip down that road was called a "Gotham Vertical".
What it lacked in performance, it made up for in education!
Google it for an evening of fun reading...
de W8CCW John

On Fri, 09 Jun 2006 02:03:43 GMT, Cecil Moore
wrote:

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

Sounds like a G5RV.
John Ferrell W8CCW

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
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
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.

Which right away spells trouble when trying to match the huge 85-75
meter bands.


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.

Or an off center fed dipole. If he can get that antenna up 50 feet,
the ends can droop down.


- 73 de Mike KB3EIA -