Jim wrote:
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.

That is very true. Unfortunately, the ham market is divided up into
physically separate compartments of transceivers, power amplifiers and
antennas. That is a severe restriction which makes all the technical
challenges much more difficult.

However, we can try to pare the problem down a little.

Another important point is that the concept of 'market demand' is
beginning to break down in ham radio. The big manufacturers are
increasingly challenged by new products that pay no attention to the
market - they spring directly from some individual or small team
deciding they're going to do it.

Then maybe the design is produced as a kit, or manufacturing is taken up
by some lower-tier company that is faster on its feet. Seems good to
me...


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.

That seems a good place to cut the problem down to size. By all means
continue to use the existing phasing networks for TX, with 4 or 8
switchable directions and fixed phasing; but switch the antennas over to
a totally separate network for RX.

At the lower power levels, the RX network could be much more complex and
versatile, combining the signals from the four (say) antennas with
amplitudes and phasing that could be varied on the fly.

Another way to scale down the problem is not to be too ambitious about
automatic null steering. In ham operating it is often difficult for a
computer to identify which is the wanted signal and which is the QRM, so
maybe let's not try. Semi-automatic null steering definitely would be
within reach, where the user has a control to steer the null direction
manually for the best audible results, and the computer does the math to
select the required network parameters.


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).

Yes, I think maybe so. We already have most of the technology for an
advanced manually steerable RX array, so it's mainly a matter of
integrating the separate parts of it to make a practical design. Someone
just has to decide to do it... and maybe they already have.


--

73 from Ian GM3SEK