TopBand: Elevated Radials

[RDTALBERT@aol.com]

Eric, Tom, Darrell,

Thank you gentlemen.  I think I finally understand the general nature of
earth losses regarding ground mounted full height and shortened 1/4 wave
resonant vertical radiators (and how to reduce these losses).

But, alas, I must ask for further enlightenment.

Unless I missed something, Eric limited his ground loss explanation to 1/4
wave vertical linear radiators (or shortened ones, i.e. series inductances or
capacitive top hats).

I experiment some with helically wound nonresonant verticals of greater than
1/4 wave electrical length - currently with 5/8 wave for 75 meters wound with
12ga THHN on 30ft of 4in PVC drainage pipe.

My question is, do the "connection", "near field", and "far field"
explanations for earth losses apply equally for nonresonant ground mounted
radiators of greater than 1/4 electrical wave length?  And, if different, in
what manner?

For instance, I recall from some research I have done that 1/2 wave and 5/8
wave verticals are supposedly less ground dependent than 1/4 wave verticals
because the current maxima along their lengths do not occur at ground level.
Is this a factual statement?  And, if true, how are the requirements for
radials affected - both in number and in length, if at all?  Does the process
of physical shortening by the practice of helically winding the radiator have
any specific effect as regards ground losses?

Tom, I know from reading some of your previous posts that you hold hellically
wound radiators in low esteem due to their narrower bandwidths and low
radiation efficiencies. Please humor me on this as I am limited at my site in
both real estate and the type and height of structures I can erect (unlike my
previous QTH where I had 15 acres and deep, conductive corn belt soils of
which to take advantage).

Darrell, you made some interesting statements regarding shortened radials and
reducing ohmic losses.  Are you refering to multiple series inductors for
each radial?  Or is there a central inductance at the base of the radiator to
which several shortened radials are connected?  As regards ohmic losses, what
would you suggest are materials of low ohmic characteristics for 75 meters or
top band?  Or is the frequency irrelevant?  Specifically, would you consider
10ga copper wire to be satisfactory?  1/4in copper tubing?

Eric, thanks for the very clear and relatively nontechnical explanation of
the various factors affecting ground losses.  I finally was able to see the
overall picture of the obstacles to be overcome in reducing ground losses.

Finally, gentlemen, I beg your indulgence.  If your replies, assuming there
will be any, of course, take a highly technical direction, I will probably be
lost.  I have the utmost respect for the work of James Clerk Maxwell and a
general understanding of the concepts he put forth.  But, sadly, his
equations are beyond my meager understanding.

Thanks and regards,

Roy     K9ER   

    

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