Topband: Re: 160 Meters Mobile Antennas

[W9UCW at aol.com]

Hi Les & Others,

As my name and call have been dragged thru this thread several times, I feel 
like I'm a part of it. I'd like to comment. The main topic seems to be 
effectiveness or loss especially related to the "Q" of the loading coil with 
a subtopic of coil form material.

First, as for the subtopic, at the time the "Minooka Special" article was 
written, the larger issue was the availability of hardware-store materials 
that could facilitate easy assembly.  We had no indications of trouble with 
PVC, didn't own a microwave, and did not sense any loss.  As I will explain 
in a moment, losses due to this form material are inconsequential.  On the 
other hand, I stopped using PVC for such purposes a long time ago, because it 
sometimes broke down due to high voltage.  I prefer phenolic tubing.

As for the HI-Q vs. LO-Q loading coil discussion, I would like to offer up a 
sampling of results from a massive study of inductively loaded verticals, 
especially mobile antennas. Most of this data was collected over a period of 
3 years at a test site built  near Fletcher, NC.  A goodly number of people 
were involved.  Thousands of measurements were made and all test series were 
repeated many times. There were near-field and far-field pick-up points and a 
dozen or so parameters were measured.

This all started with the "Q" question.  It was the big issue when I started 
mobiling on 75 and 160 around 1960. Many of us  enjoyed the increased band 
width and low amount of proximity effects of long, skinny resonators, and 
seemingly felt no difference in signal compared to the big open HI-Q coils, 
where a little rain or a small bug put you out of band.  Unscientific you 
say?  You bet.

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.

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.

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

Bandwidth is controlled by two things; the length/diameter ratio of the 
inductor and the capacitance/inductance ratio of the resonator. (Top whip or 
hat to coil inductance)….higher means wider in both cases

There are many other interesting results from the Fletcher Program, but no 
room here to cover them.  I hope what I have offered will add something to 
the discussion.

73's Barry, W9UCW