On Feb 28, 12:29 am, Ian White GM3SEK wrote:
Jim wrote:
I'll bet the hardware cost of a electronically steered phased array
for HF suitable for ham use is comparable to the hardware cost of a big
tower, rotator, and Yagi.. the phased array just isn't available as an
off the shelf product yet.

The fully steerable phased array that can also handle 1.5kW TX power is
not available as a HAM product off the shelf yet... but we can already
see where the future is headed.

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It's all down to the magic phasing box at the centre of the array.
Whatever goes into that box will be hard to design, complicated to
control, and expensive to build... but most four-square owners would be
happy to have even a fraction of those extra capabilities.

I think it might be a bit of time before it's an off the shelf product
(lack of demand is part of the reason).
It also depends a bit on just how good you want the performance to be
(null depth, primarily.. forward gain is not very sensitive to phasing
and amplitude accuracy), and whether you want to make it an antenna
system that just hooks onto an existing rig and PA, essentially
hanging off a single feedline, or whether a higher level of
integration is desirable or feasible. (for instance, rather than power
combining a bunch of solid state amp modules like the current kilowatt
class SSPAs do, put a power module on each antenna)

"the magic box in the center of the array" is more the former model,
and while simple conceptually, in the long run probably isn't the best
way to solve the problem in a system context. For instance, a multi
channel receiver, which can do all the phasing, very precisely, at low
levels, either with analog or digital processing, can give you the
nice deep nulls and adaptation.For TX, though, null depth isn't as
important as maximizing the power squirted in the right direction.

Hardware wise, the design isn't particularly complicated (any of the
current crop of automatic antenna tuners can serve as the building
block). Hard to control is mostly a matter of calibration and the
right algorithms (and, yes, non trivial, but so is building a tetrode
or FET power amp that's stable from 10 to 160, etc.). Expensive is
more a matter of "compared to what".. You can buy a kilowatt autotuner
for $500, so, assuming you needed 8 of them to control 4 elements (a
single L network can only give you 90 degrees of phase shift, and you
need 180).. that's $4K. Probably need some relays and transformers,
as well as controller. I'd figure $6K, today.. But that's "off the
shelf" assemblies. and not purpose designed. Start comparing that to
the $10K to put up a tower and a Yagi (comparing new prices to new
prices, plus building permits, etc.) and the phased array starts to be
competive.

So.. not today, but I'd figure that in 10 years, you'll start to see
real broadband phased arrays (not just 4-8 switched beams in a single
band like a 4 square). They provide a real solution to restricted
space installations, if nothing else, because you can make effective
use of the "volume" of space within a small suburban lot (i.e. the max
theoretical gain from an antenna that fits in a box that's say,
15x30x10 meters is pretty high).

Jim, W6RMK