RadioBanter - View Single Post

July 10th 03, 09:31 AM

oSaddam (Yuri Blanarovich) wrote in message

Around 1970, some guys from Argonne Labs, in an effort to show us the error
of our ways, brought down equipment to a "160 Meter Reunion" and set up a
measurement program. About 75 people were there. On the "Q" question, the
comparison was between similarly laid out center/top loaded antennas. One
had a big open wound, heavy wire, spaced turn coil with a 8" diameter and a
1:1 length/diameter ratio. The other had a 1" diameter close wound coil on a
PVC form using #20 wire. The length/diameter ratio was over 20:1. It was
covered with shrink tubing.

The measured worst case scenario (of any HF band) was on 160. The difference
was .3db. That's 3 tenths. We were all shocked and immediately agreed that
the test had to be flawed...even those of us that thought the LO-Q coil was a
better deal. It just couldn't be that close.

I wonder how much ground loss they had...

That test was modified and tried over and over. I know of 5 more run between
1972 and 1992....all with the same results. Personally, the big beasty open
HI-Q coils look like "real radio" to me. There's just no real reason to use
them unless you prefer pinpoint bandwidth and terrible "proximity" problems.
We reconfirmed the numbers in the Fletcher Program.

The reason the difference is small is that the current diminishes so rapidly
in the first few turns of lumped inductance, whether Hi-Q or LO-Q, and
therefore only the loss in those turns is being compared. The same is true
for inductively top loaded base station verticals. Loss in the coil is
insignificant. Most calculations to the contrary made in texts, articles and
some modeling programs are based on the current being equal throughout the
coil. This is not true. Of course, most mentions of this loss are not
quantified at all.

Again, I also wonder about ground loss. If the amount of ground loss
is high, it's ratio against coil loss is higher. A lossy coil might
not be much of an impact. But a low loss ground system would make a
lossy coil show up more being the ground loss is a lower part of the
total.

On the other hand, the position of the coil in the available vertical mast
means everything. Here's the bottom line: All other factors being the same,
the inductively loaded vertical with the longest mast between feed point and
lumped inductance wins the radiated field strength contest.

I agree with this part for most cases.

This means that
a standard Hustler setup is louder than any "Screwdriver" or "Bug Catcher"
unless they have more than
4Â½' of mast below the coil.

But, this is just pure finely ground sandwich meat. In the cases where
I tested, I never saw a hustler coil even approach my homebrew coil or
any other equal size coil for that matter, and at that time, my
homebrew coil was only 2 ft above the base. I tested the hustler on a
3 ft solid mast. It was waaaaayyy down. But they also use those stupid
short stingers, and hence use more coil windings than they really
should. Hustler is a special case... Also, note the test results
Cecil just posted...His results using the hustler seem to match mine.

We confirmed that in Fletcher, too. As an
example, for 80M, a 9ft. top loaded mast was down 20.5db from a full quarter
wave, both measured on the test stand. The base loaded 9 ft. mast was
36.5db down, a difference of 16db. BTW, the same mast loaded with a Smart
tuner or Icom AH-4 was 44.5db down. Results are worse on 160.

I assume the 9 ft top loaded ant was the hustler...??? I notice they
don't mention the center or near top loaded bugcatcher coil in
comparison...Sure, a base load is going to be down...

Seems that Hustler tried to "match" the low band resonators by introducing some
extra loses in their loading coils. I rewound the resonators with 1/4" copper
tubing (20 and up) but in view of W9UCW findings maybe there is good compromise
between ugliness and performance.

I think the 1/4 inch tubing is overkill. Really , I think anything
over about 2 mm wire size is starting to be overkill considering the
increase you get. But, I am not a fan of hustler coils. I won't use
them. All the antennas I've made using those coils were "dummy loads
on a stick". That includes the 80-10 multiband vertical I tried that
used those resonators.
I've been thinking about the disparity some seem to see in coils. I'm
starting to think it's differences in ground loss. The less the ground
loss, the more a lossy coil will show itself. Enough loss, anything
might seem ok... MK