On 8/11/16 10:28 AM, Richard (Rick) Karlquist wrote:
On 8/11/2016 8:48 AM, Hans Hammarquist via TowerTalk wrote:
I have had an idea for some time: When you feed all these stacked
antennas in phase you will have optimum radiation to the horizon (or
just above). My idea is to add switchable delay lines to the higher
located antennas. (You could rather easily replace the damping
networks in an attenuator with some coax do make this.) Thereby you
will be able to get optimum angle for "higher up" propagation. You
should select the steps to be small enough not to get "gaps".
Any taker? (K1TTT?)
Hans - N2JFS
I tried modeling stacks with phase shifts of both polarities
and was never able to come up with a configuration that seemed
like it would be useful. It is one of those "squeezing on a
balloon" problems.
Although you describe this as "your idea" it is inconceivable
that it wasn't around decades ago. If it made sense, someone
would be doing it. As you say "beam tilt" for UHF TV antennas
is something else again and not analogous to HF radio.
phasing a vertical stack has been done for HF for a number of decades.
Systems like the "woodpecker" are an example.
Radio France International has some huge steerable arrays, as well.
I'm not aware of any hams doing it, other than a BIP/BOP scheme which
flips the phase.
I think that for most "real time adjustment" scenarios, a
BIP/BOP/TOP/BOTTOM of sorts is probably as good as anything else. That
lets you move the nulls in the pattern around in elevation, so you can
place the null on a strong interfering signal(s), to dig out the faint one.
Using switched transmission lines (coax) as delay lines is the classic
"true time delay" scheme for a wideband phased array.
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