Rik van Riel wrote:
> On 11/27/2010 09:08 PM, Rick Karlquist wrote:
>
>> VK1OD did a nice analysis. Unfortunately, many hams are simply
>> in a mode of "don't bother me with facts". They desperately want to
>> believe in the paradigm of a tuner in the shack and a simple all band
>> antenna at the other end of the line, such as a plain vertical
>> conductor,
>> or a random wire, or a "loop skywire", a "G5RV," or some sort of
>> "Windom"
>> antenna. All continue to live on in ham folklore.
>
> The big horizontal loop antenna seems decent, provided it is
> cut at a length that gives it a good match on not just the
> primary band but also the others:
>
> http://surriel.com/radio/multi-band-hf-loop-antenna
Are you kidding me? The pattern breaks up into a multitude
of lobes on the higher frequencies. This is the fundamental problem
with any simple conductor used on many bands with a shack based tuner.
If you shorten the conductor to fix this problem, then the
efficiency on the low bands goes way down. A tuner in the
shack doesn't really solve this.
When you have a multi lobed pattern, once in a while you get
lucky and that new country falls on a lobe and you work it.
One of many reasons not to use DXCC to evaluate antennas.
Also, as has been pointed out, propagation is funny. In
the recent CQWW test, I called a rare African DX station with a
huge pileup, and then noticed I was running barefoot. Before
I could turn on my linear, the station came back to me on
my first call. I think we just had a pipeline in the sky
by luck. It's not like I didn't need the linear for the
rest of the contest.
To make one antenna work well over many entire ham bands, you either need a
screwdriver type design, or a SteppIR design that retunes
the antenna vs frequency. The screwdriver must be less than 5/8 wave at
the highest band to avoid breaking up the pattern, which in practice it
will tend to be anyway if it is used mobile.
Rick N6RK
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