On 6/14/13 5:06 AM, PY1NB - Felipe Ceglia wrote:
Hello folks,
I'd like to hear your opinions about this topic.
I am looking for an antenna (or more than one) for 10/15/20m that has the
following characteristics:
- vertical polarization
Well then, either a vertical element or a horizontal loop as your
radiator(s).
- smallest possible horizontal far field lobe
Not sure what you mean by this. Do you mean you want low gain "at the
horizon"? That isn't usually what DX wants, where you want good gain at
low angles. Are you looking to suppress local noise sources that are on
the ground?
- "good" forward gain (at least comparing to a single element vertical)
gain or directivity. Later you talk about using this for Rx only. For
HF, receive noise is dominated by atmospheric noise sources, so gain
isn't usually the big deal, what you want is good directional behavior?
- greatest possible front to back ratio
Front to back, or good nulls? or front to sidelobes?
I was thinking about using:
- a tribander tilted 90 degrees
It has to be up fairly high so that the interaction of the elements with
the ground doesn't bite you.
- 2 element end phased array of:
- vertical dipoles
- sitting on the ground verticals (with or without radials?)
- multiband verticals (using W9AD phasing line to switch between bands)
- 5/8th wave verticals (at least for 10m, it would be easy to convert CB
antennas)
- a 4 square
All of these are generically the same: none have particularly narrow
forward beam. 4 squares and the like are nice because you can quickly
swing the null to put it on the interfering sources.
Two verticals with adjustable phasing can work very well to null signals
coming from one direction, which may be all you need. There was an
article in one of the antenna compendiums where an adjustable L/C
network was used as a variable phase/amplitude shifter.
The W9AD scheme from array solutions is similar, using coax as delay
elements (although the original scheme with adjustable L and C also
allows adjusting amplitude, which will get you a much better null)
One thing to bear in mind on any of these approaches is that phasing
errors don't change forward gain very much, but a small phase error
turns a -20dB null into a -10 or -3dB null. (this is probably the
source of the 4square complaints about installed performance..)
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