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[Towertalk] Re. HF2V

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Subject: [Towertalk] Re. HF2V
From: (Tom Rauch)
Date: Sun, 7 Jul 2002 07:24:37 -0400
> 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 

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 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 

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