TopBand: Slow wave antennas

[km1h@juno.com]

I appreciate and agree with  most of your comments Tom but I still have a
problem with your distributed inductance "here and there" ideas.

My understanding of the basic Beverage and any antenna that utilizes VP
as an important factor is that it behaves as a transmission line. I may
be wrong here and welcome others to comment.

One does not introduce lumped reactances into a transmission line without
a full understanding of the consequences and the means to measure and
control them. Your point about being able to measure phase shift, and
magnitude I assume, is well taken but not available to the masses. It is
not something tobe measured by  an MFJ Analyst  toy for instance. Not
everyone has access to real test equipment such as HP. 
BTW, as an aside, I do have a nice HP-4815A vector impedence meter here
but no probe. Do you or anyone else have any info on constructing one? It
only has to be accurate thru maybe 7MHz; not up thru VHF as the original.


Next, by placing lumped inductances in the wire at selected intervals
would seem to limit the antennas usefullness to a single band or maybe
selected harmonics. I still have a very hard time understanding how
periodically slowing the VP and then speeding up will result in a good
performing antenna....Im trying to relate this to the incoming wavefront
which is a constant. 

The Slinky, if stretched equally thruout, exhibits a constant rate of
change...VP,  as does the straight wire Beverage.  Granted, it is not
easy to determine the optimum length or pitch yet but it does not defy
computer analysis. Altho its damn well beyond my capabilities I am sure
someone with a ton of smarts, access to NEC-4 or both will work it out. 

Also I feel that any version dependent upon sufficient lumped inductance
to slow the VP to half would be pretty inefficient, ie....lots of coil
loss in a pratical installation. A 160M dipole using loading coils to
halve the physical length is a fairly lossy device as an example.
Helically wound loading is more efficient. 

There is no claim that the Slinky Beverage is as good as Sex...not yet
anyway. It does, IMHO, offer a simple easy way for someone with limited
space to improve low band reception. Thats fact...not fiction; I and
others have proven that beyond doubt. On 160M it is better than my full
sized 2el phased array. On 80M it is often superior to a full size 4
Square.  By superior I mean S/N, not absolute signal levels.  Perhaps Tom
your reference to high side nulls is the factor; even a 4 Square is as
broad as a barn door compared to a multi wavelength Beverage. 

The Slinky is just the latest in a long line of ways to fight Mother
Nature on the low bands. I claim no "inventor" status....my initial use
back about 10 years ago started as a joke and dare as the result of an
"after midnight" 160M SSB roundtable. I have resisted up to recently even
discussing it with all but a few since I do not have a way of proving the
performance. Publishing without supportive data would put it into the 73
or CQ Magazine category along with the rubber duckys on the helmets and
15dB gain LogPeriodics on half wavelength booms.

I hope that this long winded post will stimulate others to respond and
also experiment.

73....Carl    KM1H 

 

  

As you pointed out, the limits to slowing the wave AND patterns AND
efficiencies are only generalities so far; they need more analysis.    

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