On Mar 2, 12:15 pm, Richard Clark wrote:

If you are interested in a design for yourself, and maybe a production
run of a few hundred, then look to the HF/10M/6M/2M surplus repeater
market from Motorola and RCA designs of the 70s and 80s. Dirt cheap
decks with enough elbow room to make mods.

Or, perhaps the HF Superpacker Pro.. 100+Watts..20dB or so gain.


Fortunately, the problems are solvable, at least in a theoretical
sense.

One doesn't usually see fortunately paired with theoretical.
ironically this is how this thread started - was with a pig in the
poke explanation passing for science

A heck of a lot better than "theoretically there is NO solution..."
girn

All you need is a few kHz, so a single L and C might do it,
"good enough".

So, this daydream is on one band only?

1 adjustable L, 1 adjustable C.. covers all bands. For ham
applications, you only need to have the match and phase adjust at one
frequency at a time, and over a fairly small bandwidth, so the Q of
the matching circuit can be high. Not like a generic wideband phased
array where you need to have a wideband match, and do something like
true-time-delay processing.



OK, Analog Devices is a star performer. I built a tube version of
this DDS back in '68 when it was called a coherent detector (could
have been called many names depending on where you developed the audio
output).

However, this is NOT what I was referring to, as that is distinctly
different. This is a software controlled oscillator whose frequency
and phase is immediately settable (within on clock, this is in the
nanosecondS range).

That is precisly what a DDS does.. It has a phase accumulator where
you can adjust the phase increment per clock. The output of the phase
accumulator goes to a sine lookup table and then to a DAC. A typical
part might have a 48 bit phase accumulator and a 12 bit DAC.

Check out, for instance, the AD9858..

You might not be able to update the phase increment or absolute phase
in a nanosecond, but it's pretty fast (there's some pipeline delay
too.).. I'd say you could clock in a new configuration and have the
new RF appear no more than 100ns later.

If you need to phase each array element
independently to phase steer the combined system (also to take care of
phase matching through mutual coupling), the software solution spring
immediately to the front for a solution.

Well, software for the calculations, but perhaps not for all the RF
processing. You still need to adjust Ls and Cs for the match, unless
you're willing to design a fairly unusual amplifier: ideally, it would
act like a current source with a lot of voltage compliance that can
tolerate a very reactive load.. so you're essentially synthesizing the
L and/or C with an active device.. doable, but not too hot on power
efficiency these days.

Interestingly, in a very much higher budget arena (deep space comms
and ranging), they're also doing this. Until recently, you had to
special order the crystal for your spacecraft radio (with 18+ month
lead time!!), so if you had a channel reassignment, it was a real
problem. (One of the Mars Rovers and the Mars Reconnaissance Orbiter
are on the same channel.. wasn't supposed to be a problem because the
rover was not planned to survive long enough)

The software oscillator I described in the previous post would solve
that for the same cost as the custom XTAL.

Well.. not the same cost as a custom rock. The rock may have a long
delivery time, but it's not particularly more expensive than a
standard frequency. The DDS doesn't come for zero power, either, so
you have a tradeoff of more DC power for flexibility (power
consumption is a very big deal in deep space exploration). And, then,
there's also the whole radiation tolerance issue.


If you are looking for a design and a market, I cannot think for the
life of me why that hasn't happened yet.

Systems like this exist, but not in the ham market. Oddly, it seems
that hams balk at forking out more than $100K for a system that does
all this. The challenge is in getting it in a ham friendly format.
The hardware's not expensive, it's all that software and system
integration. But, 10 years from now, when the early adopters have
cobbled together their systems from bits and pieces, and some of the
concepts become more familiar, I think you'll see someone make the
investment to do the development to create an off the shelf product.
Clearly, there is SOME market for $10K ham widgets or things like
IC7800s and big towers with arrays of SteppIRs wouldn't exist.





73's
Richard Clark, KB7QHC