> At 11:11 AM 8/23/2006, Keith Dutson wrote:
>> >It is simply not true that a larger antenna transmits better than a
>>That's a pretty broad statement to make. If so, how come all the big guns
>>use very big antennas?
< snip >
> If one had an unlimited budget and some time for experimentation, one
> do better than the existing things that are available, and likely the
> antenna itself would be physically smaller. The problem is that the value
It depends on what you mean by smaller but in the normal sense, I doubt it
would work out that way. The design programs will show a "full size" yagi
should perform the best compared to well... yagis that are not full size.
IE, either larger or smaller. It's true that there is no one optimum set of
element lengths and spacing that will provide the highest gain and the best
front to back ratio, but we are still talking full size.
> of "doing better" is substantially lower than the available development
> budget, and, there's no guarantee of success (particularly as a commercial
All multi-element antennas are a compromise be it exchanging gain for front
to back ratio, available boom length, number of elements, or what ever.
Multi-band antennas are much more extreme conpromises. Even the SteperIR is
a compromise albeit what appears to be a very good one. They can vary the
element lengths to get the best gain OR F/B on a given band, but they can
not vary the element spacing. This does make for a larger than needed
antenna on specific frequencies, but here they exchange size for utility.
Tribanders are probably the biggest set of compromises most of us run into
on a dat-to-day basis. By using traps of stubs they manage to operate on
multiple bands. Usually their dimensions are considerably smaller than what
would provide optimum performance, but again we are exchanging size for
utility. These antennas although flexible, generally confine us to one
portion of each band as they are not adjustable for frequency in real time.
When you get to 40 meters the full size antennas are head and shoulders
above the smaller versions. Of course on this band the big antenna on the
big tower is normally better than the big antenna on a roof mount. @0, 15,
and 10 are different stories. If you run the figures I think they'll show
for a single antenna on these bands little is to be gained by going much
higher. You do get a lower take off angle, but you want a take off antle
that gets you to where the band is open, and that is not always the lowest
as many on here who can switch antenn heights have attested
> The other factor driving to tall antennas is the advantage you get from
> height above ground, particularly in the ham "legal power limit"
> context. You can't afford to give up the "ground reflection gain" by
Sure you can if the take off angle it lower than optimum for the day.
> low. Someone operating without a power limit wouldn't be faced by this
> issue, which is essentially "antenna" independent (but not "tower
> The fallacy is in comparing BIG antenna on BIG tower to SMALL antenna on
This is of course the apples to oranges comparrison.
>It's the BIG tower vs Rooftop that's the killer, not the physical
> antenna size.
I'd say it's a combination of height, antenna size, and frequency.
Contrary to what many say, size does make a difference.
Oops that came out sorta sounding like antenna envy and I have a small
But it is on top of a tall stick.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com (Use return address from home page)
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