> N4KG: For the most part, this is true, until you reach 250-280
> and have to work over the poles to finish off the rest, THEN
I've rarely is even worked over the poles on any band below 40
meters. For example, the normal path from here to Mongolia is SE in
the evening and SW in the morning. Same for deep Russia and India on
160 and 80 meters.
> transmitting performance makes the difference between getting
> there and NOT. When I added my 130 ft high dipoles, Central
> and SE Asians became MUCH easier to put in the log.
Everything is all relative to what we compare it to.
> > One reason so many people have dismal results with base-loaded
> > antennas is they swallow the "BS" about only needing a few radials.
> >
> N4KG: True. KZ4V had 120 radials under her base loaded HF2V
> with NO top loading wires. The radials were probably in the range of
> 35 to 40 ft which admittedly reduced performance on 80M.
There is a problem tossing around anecdotal evidence to determine
performance, and we should all be aware of the problem.
Factually, once .025 to .05 wl spacing is reached adding more wires
does no good at all. So 50-60 radials would have worked just as well
on 40 meters, and on 80 she might as well have had 15-30 radials as
120.
It would not sound impressive if we said "she had 15 1/8th wl
radials", yet the system would be about the same as 120 radials the
same length.
The person listening to the story hears "120 radials" and hears
"empty lot", and doesn't think about the fact the system was actually
a modest or poor radial system and there could have been any number
of problems with the rest of the installation, such as site clutter.
It is only on 20 meters and higher than the 120 radials helped, and
only then a fraction of a dB over having 50 or 60 radials.
> The REAL convincing observation was that she moved from being
> one of the LAST to get through the pileups with her HF2V to being
> competitive in the pileups after her 90 ft tower was installed with
> the inverted vee and vertically polarized Delta Loop. These antennas
> were obviously MUCH more competitive in the pileups.
That isn't necessarily a problem with the HF2V, and we should all
know better than to leap to that conclusion based on the data.
Had she A-B'ed a full size vertical in an open location at the same
site under the same band conditions and seen a change, it would
indicate an efficiency problem with the vertical system, location,
or ground system. Changing to a dipole (especially when comparing
anecdotal data to anecdotal data taken at a different time) proves
nothing, because it could be any number of things at work.
One thing often overlooked is the distance required to minimize
pattern distortion. On 160 meters, a tower 500 feet away from my omni
vertical changes the pattern about 10dB in four directions! On 80
meters, think of all the vertical or near vertical metallic
objects...let alone all the other variables at work.
Now I know the Gap vertical is no good, because I tried one with a FS
meter and had a good ground system under the reference antenna. i
also A-Bed them.
Factually, an MFJ 80/40 top loaded vertical and a Butternut were
about even...and the Gap was 10-15 dB behind. How many countries I
worked on each or how they worked in pileups is immaterial, because
of all the inconsistencies in other factors important to results.
> > Factually, there is almost no difference between base and top
> > loading if the ground system is good. Top loading does provide
> > about
> four
> > times the radiation resistance of base loading, but top loading
> > generally has (for a given radiator size) less bandwidth.
>
> N4KG: HUH? Since when does higher radiation resistance result
> in "LESS BANDWIDTH" (assuming the same height of radiator) ?
In heavily loaded systems with fixed external losses, bandwidth is
mainly set by reactance limits. The antenna can be viewed as a series-
resonant L/C system. Anything that decreases the amount of reactance
increases bandwidth, because it decreases system Q.
For example, my narrowest mobile antennas are the antennas with the
SMALLEST amount of capacitance above the loading coils, regardless of
efficiency or radiation resistance.
As a matter of fact the widest bandwidth antenna I have has the
highest efficiency. You have to look at the entire system, and NOT
just relate bandwidth to one factor.
The MFJ vertical is VERY narrow in bandwidth because it has a small
top-hat, and large inductor. The same antenna has nearly eight times
the bandwidth when base loaded, and if the ground system is near-
perfect efficiency can actually INCREASE.
The top loading makes the system more forgiving of poor ground
systems and allows you to use the antenna on 40 meters, but it also
makes the system have LESS bandwidth.
> > If the ground system is poor, top loading can reduce loss by up to a
> > factor of three or four. If the ground system is good, efficiency
> > changes are often not measurable.
>
> N4KG: What value of ground resistance is "good"?
> What does it take to reach this level?
Ground loss would have to have a normalized value (at the feedpoint)
of about 10% or less of the other resistances in the
system...including radiation resistance...in this example. So 40 1/4
wl radials would work in most cases.
Brown Lewis and Epstein did all this in the RCA report "Ground
Systems as a Factor in Efficiency". Their conclusion, and one that I
have verified, is that with a good ground system you might just as
well base load the antenna.
> > Most of the DXCC totals do with hours operated, location, and
> > operating skill. I'd say transmitting antenna performance is way
> > down the ladder, unless someone really has a poor antenna
> installation.
>
> N4KG: Again, basically true UNTIL you start talking about polar path
> contacts.
Polar path contacts virtually never occur on 80 or 160 meters, and
rarely occur on 40.
73, Tom W8JI
W8JI@contesting.com
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