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Richard Clark · March 2nd 07, 06:32 AM posted to rec.radio.amateur.antenna

On 1 Mar 2007 21:16:22 -0800, wrote:

Dare I say that what is needed is that much overworked phrase
"paradigm shift"? It used to be that a "transceiver" was a radical
new thing, because everyone knew that you needed a separate Tx and
Rx. Oddly, with phased arrays, perhaps the transceiver becomes passe.

Hi Jim,

There may be life left in the transceiver to perform what you want
anyway. Just think more power.

I can sense that this discussion is leading back to a separation of
driver from amplifier. You could still use a power divider to feed
the remote amps at the various array locations. Say 10W at 10 active
antennas, each with a 100W rating.

This would preserve investment, and create and alternative to the
Henry market. Hams would have two purchase paths instead of
discarding their introductory base station and opting in for N number
of active arrays driven by a specialty item that looks like their old
rig gathering dust in the corner.

Of course, if you are talking about two or three elements, this shifts
the investment plan (but it still presumes you are willing to abandon
a prior investment). The cost-benefit of this is usually a steep
slope populated only by a few early adopters.

In fact, for HF, you can probably get away with smaller active
antennas for receive. There's no particular reason why the Tx
antennas and the Rx antennas have to be the same, since you're not
typically receiver noise figure limited.

There's no reason to expect you need a large transmit antenna for
solid state amps either. The native source resistance of a transistor
is quite low, and has to be transformed UP to match 50 Ohms. If you
had a radiation resistance of only several ohms (a very short
radiator) all you have to pay attention to is cutting Ohmic loss and
providing flexible inductance. Unfortunately, this may be a
performance killer - but if you are demanding multiband performance,
you will have to answer for this for any size array element.

There IS a strong signal IM
problem..so maybe active receive antennas aren't the right solution.

The same transceiver that survives IM would still handle it from
several phase active array elements. As you can see, redesigning a
new driver eventually leads you back to the gear you have. If you now
demand a separate receiver, separate driver, and separate active array
antennas, costs rise faster by the number of connections.

Adaptive nulling is a bit weird to
work with as a user, especially if you expect to control it. And, for
hams, they want a bit more control.

Programmable oscillators that shift immediately and start at any point
in the cycle (absolute phase AND frequency control) would be miles
further down the road.

These devices are NOT synthesizers NOR linear multipliers. They are
variable frequency look-up tables driving a DAC. You send the chip a
command of the frequency you want, and the phase angle; send the "go"
command, and the oscillator shifts from its existing frequency and
phase immediately to the new one (immediately being within one table
cell lookup).

When I looked into these 10 years ago, they (driver/DAC combination)
operated from the KHz up to about 16MHz and cost less than one XTAL
ordered to a single frequency. You still have the elemental clock osc
XTAL for processor and driver, but those litter the world for pennies.

Using this kind of technology is about the only reason I would trash
my current rigs and go for a custom driver (but it would have to
inhabit each array antenna's amp and thus render it a complete
transmitter. This would in turn cast all the features (like SSB
generation) into each of those elements. The unit cost of this would
climb because of feature creep, not component pricing.

What would be cool is to have a
3D panoramic display that somehow indicates not only the frequency
spectrum, but the angle of arrival.

This again, argues for small adaptive antennas. Now you need them in
layers.

73's
Richard Clark, KB7QHC