On 1/17/12 7:35 AM, Ken wrote:
>
> On Jan 17, 2012, at 9:35 AM, Jim Lux wrote:
>
>> No, but you could do it by having a very low loss matching network and a
>> physically small radiator.
>
>
> You are trying to tell me that if I had an excellent matching network, I
> could use a 2m dipole on 80m and it would be just as effective?
>
> Sorry, I think you are confusing feed and matching losses and ignoring an
> effective radiator. There is no way that I will believe that a "physically
> small radiator with a very low loss matching network" is as effective as a
> half wave antenna.
>
What does "effective" mean?
If you define it as "getting RF power at the feedpoint launched into
space", ANY size lossless antenna works pretty much the same. That are
differences in the spatial distribution of the energy: some antennas are
more directional than others.
So, yes, theoretically, you could use a 2m dipole on 80m. However, you
cannot do this "practically" because the excellent matching network you
would need cannot be built with actual materials.
There are some fundamental limits on antennas which relate size,
directivity, and stored energy in the antenna.
The challenge of antenna design, in the real world, is choosing which
components to use and what compromises to accept. Do you go with end
loading of some sort which changes the current distribution in the
shortened antenna, and so changes the pattern slightly, and makes the
feedpoint impedance a little less annoying to match, at the expense and
hassle of the end load itself? Do you use multiple L/C in a matching
network to get low loss and good match in multiple bands, or do you use
multiple elements like in a fan dipole.
For a not too short dipole (say, >75% of normal length), the added
losses in antenna and matching network won't be very big. And
pattern-wise, there's almost no difference between the 75% length dipole
and the full size.
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