hello
thanks to all for the help about that.
Will update on my project!
73,
Jorge
CX6VM/CW5W
El jue., 16 may. 2019 a las 18:25, jimlux (<jimlux@earthlink.net>) escribió:
> On 5/16/19 1:00 PM, Jorge Diez - CX6VM wrote:
> > hello
> >
> > I want to build a 4SQ system, with four aluminium vertical antennas
> >
> > My terrain is not flat, so I will do some work to level the ground
> >
> > My question: is just enough to level the terrain where the 4 antennas
> will
> > be placed or is also necessary to level all the field included the field
> > occupied by the radials?
>
>
> A 4 square is 4 vertical antennas with the element currents set by a
> phasing network - typically, the phasing network uses 1/4 wavelength
> lines to "force" the currents to be the right ones, using some form of
> 90 degree hybrid at the common feedpoint.
>
> The answer to your question has two parts:
> 1) Assuming the element currents are phased as expected, how much will
> the pattern be degraded by non-ideal elements?
> 2) Is the element current phasing perturbed by non-ideal elements?
>
> For #1 - 1/4 wave monopoles are pretty tolerant of their radial field
> variations - the gain and phase don't change very much - it's all about
> the current distribution in the vertical element and the "sort of
> complex" reflections off the soil surface in the near field. You can
> look at N6LF's page for a discussion of the (small) changes in pattern
> of a 1/4 wave vertical.
>
> My opinion - not a big deal as long as you're not talking about putting
> it on the side of a cliff, or the "lumps and bumps" in the soil are a
> "significant fraction of a wavelength"
>
> For #2 - non-uniform ground systems and installation in general will
> change the mutual impedances of the antennas, which will change the feed
> point impedance. If you were using a simple feed system that assumed
> everything had 50 ohm feeds, it would definitely be degraded. Note well
> that a typical 4SQ in ideal situation has feedpoint impedances that are
> nowhere near 50 ohms.
>
>
> However, most 4SQ setups use the 1/4 wave (or 3/4 wave) "current
> forcing" scheme. So now, you're really talking about how well does your
> 90 degree hybrid work when working into an unexpected load impedance.
> And that's something that's hard to know - I suspect a lot of folks have
> this, and aren't aware of the problem.
>
> And here we come to the actual question - what performance number do you
> care about?
> If it's forward gain - 4SQ type phased arrays can tolerate huge changes
> in phase angle/amplitude without greatly affecting the gain. We're
> talking 0.3 dB kinds of changes with a 30 degree phase error
> [(3+cos(theta))/4 = 3.87/4]
>
> If it's sharp nulls - yeah, small changes of a few degrees turn a 20dB
> null into a 10dB or a 6dB null.
>
>
>
>
>
>
>
>
>
>
> >
> > Would be very good to level ALL the terrain that will be occupied by the
> > radials and antennas, but if it's enough to level just the place of the
> > antennas, will save a lot of money
> >
> > thanks!
> > Jorge
> > CX6VM/CW6W
> >
> >
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--
73,
Jorge
CX6VM/CW5W
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