Jim,
I have been dreaming about the same kind of active TX/RX array you are
talking about. Since I have been considering doing it for 160m QRP, I have
envisioned each "final amp" to be broadband opamp-like current source that
can drive a reactive load. That way I can use non-resonant verticals. I
figure that is pretty do-able at 1.6Mhz. As you said, efficiency is not
always an important goal. I didn't consider the fact that the antenna
losses could be considered losses in the source, but I admit that is pretty
clever. You have a very good point there.
I might be smoking the same stuff you are, since I had already realized
that one advantage would be somewhat arbitrary placement of the elements of
the array. I have been putting this project off for about two years while
working on getting a software consulting business off the ground.
I like to call this SDA, for Software Defined Antenna. But since,
active phased arrays are nothing new in the radar field, lets call this ASDA
for Amateur Software Defined Antenna.
Dudley - WA1X
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of
towertalk-request@contesting.com
Sent: Friday, March 04, 2005 9:02 PM
To: towertalk@contesting.com
Subject: TowerTalk Digest, Vol 27, Issue 16
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Today's Topics:
1. Orion rotator (follow on) (Richard (Rick) Karlquist (N6RK))
2. Re: Orion rotator (follow on) (TexasRF@aol.com)
3. Re: amplifiers for phased arrays (Jim Lux)
4. Re: amplifiers for phased arrays (Tom Rauch)
5. Re: amplifiers for phased arrays (Merle Bone)
6. Re: amplifiers for phased arrays (Jim Lux)
----------------------------------------------------------------------
Message: 1
Date: Fri, 4 Mar 2005 12:44:03 -0800
From: "Richard (Rick) Karlquist (N6RK)" <richard@karlquist.com>
Subject: [TowerTalk] Orion rotator (follow on)
To: <towertalk@contesting.com>
Message-ID: <MGEKKFGEAIKJOOPJPGIKCEOFFBAA.richard@karlquist.com>
Content-Type: text/plain; charset="iso-8859-1"
I posted recently about a rotator that
looked like the OR2800 on M2's web site.
I opened it up and discovered that it
has an AC motor and a 500 ohm pot, not a pulse
generator. The motor label said Orion
on it. I am wondering if this is some
older model.
I have a T2X control box. It appears
I should be able to use it with this
rotor. Possible problems would be wrong
pot resistance, or not enough 24VAC power.
Just wondering if anyone has any thoughts
on this.
Rick N6RK
------------------------------
Message: 2
Date: Fri, 4 Mar 2005 15:56:19 EST
From: TexasRF@aol.com
Subject: Re: [TowerTalk] Orion rotator (follow on)
To: richard@karlquist.com, towertalk@contesting.com
Message-ID: <97.5a7613ca.2f5a2573@aol.com>
Content-Type: text/plain; charset="US-ASCII"
The original OR2800 had an ac motor and direction sending potentiometer.
73,
Gerald, K5GW/Texas Towers
In a message dated 3/4/2005 2:45:48 P.M. Central Standard Time,
richard@karlquist.com writes:
I posted recently about a rotator that
looked like the OR2800 on M2's web site.
I opened it up and discovered that it
has an AC motor and a 500 ohm pot, not a pulse
generator. The motor label said Orion
on it. I am wondering if this is some
older model.
I have a T2X control box. It appears
I should be able to use it with this
rotor. Possible problems would be wrong
pot resistance, or not enough 24VAC power.
Just wondering if anyone has any thoughts
on this.
Rick N6RK
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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------------------------------
Message: 3
Date: Fri, 04 Mar 2005 16:38:02 -0800
From: Jim Lux <jimlux@earthlink.net>
Subject: Re: [TowerTalk] amplifiers for phased arrays
To: "Dave Bowker" <dbowker@mail.sjv.net>, <Towertalk@contesting.com>
Message-ID: <6.1.1.1.2.20050304151206.0279af28@mail.earthlink.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 01:44 PM 3/4/2005, Dave Bowker wrote:
>The performance of any phased array is critically dependent upon proper
>[phasing] and [amplitude] of the power delivered to each element in the
array.
Sure
> If we consider only the transmitting case, this is almost impossible to
> accomplish with what your are proposing.
Nope
>The phase from the central feed point to the input of each element
>amplifier can readily be controlled, but how do you plan to control the
>phase shift through each amplifier at the element?
One calibrates the system, at full power (because phase shift through the
amplifier varies with power). In practice, one calibrates the components
infrequently to get close (i.e. you build up two port models (over
frequency) for the amplifier, and for the tuning network). You also measure
the mutual impedances between elements of the antenna. Then, on the fly,
you calculate a first estimate for how to configure it (using standard
network analysis), apply power, and tune for maximum smoke with an
optimizer.
Really, it's not much different from how antenna autotuners work. Either
they start from scratch and go through an iterative process to get a match,
or, they look at the current frequency, and use a previously memorized set
of settings.
>No two power amps exhibit the same phase shift when matched to the load
>impedance ... PERIOD
Which is why one calibrates.
>... there are literally an infinite number of L/C combinations which will
>match the amp to the load, but each one exhibits a different phase shift.
Not quite an infinite number of L/C combinations.. turns out there's
actually relatively few, particularly if your tuner adjusts L and C in
discrete steps. The real complication is that your load impedance (the
element driving point impedance) is a function of all the other element
source impedances.
As far as the phase shift of the adjustable networks go, they are both
measureable, calibrateable, and calculatable. They're relatively stable (in
the minute to minute sense) passive devices. One can fairly quickly step
through a sequence of Ls and Cs and remember what the two port parameters
of the device are. Then, when in use, you can get fairly close by
calculation, then bump up and down to optimize.
Considering 4 elements, you'd have, typically, 12 variables to play with:
the phase of the signal going to each amplifier, the L and the C of the
matching network. You can calculate the initial guess, then, in the space
of a few seconds, try bumping each one up and down one step and see which
one produces the desired element currents to match the calculations.
> Amplitude control is possible (at great expense of complicated
circuitry),
Amplitude control is actually fairly trivial, particularly at low
powers. A diode attenuator will work. An even easier way is just to
generate appropriately phased and amplitude signals using something like a
DDS (or, for example, a SDR-1000, which uses a DDS and I/Q
upconverters). On the low power side, you don't care much about
mismatches; it just changes the phase (maybe) and the power, which you want
to do anyway. The key is the ability to calibrate what you get. It doesn't
have to be particularly linear (in the sense of constant dB per volt, for
instance)
> but each element of a phased array must have precise [phase ]AND
> [amplitude] of power applied to it.
>
>And how do you propose to handle the reverse situation (on receive) ...
>the amps you are contemplating ARE NOT BI-DIRECTIONAL !!!
One doesn't really want to use the same technique on receive anyway. The
optimization strategy is actually quite different on transmit and receive.
On transmit, the objective is to squirt the maximum amount of power in the
desired direction, but if there's a sidelobe, it doesn't matter. On
receive, the objective is to have the minimum response in directions you
don't want. What you really want is adjustable nulls.
It also turns out that on receive, there's a significant advantage in
having more elements, preferably with different polarization
characteristics, so that you can use adaptive beamforming. On transmit,
because you don't know what the path looks like to the "other guy", there's
no advantage in trying to do polarization diversity.
>I don't think what you are contemplating is realistic from an engineering
>point of view, let alone economics!
It's extremely realistic from an engineering point of view (as in, it's
been done before).
As far as economics goes... sure, it's not as cheap as a rockmite and a
wire, but then, it's not all that bad.
Here you go with a typical equipment stackup:
4 SDR-1000 digital radios (w/100 Watt output) - 4@ $1300
4 SGC500 500W amplifiers - 4@$1200
4 high power computer controlled tuners 4 @ $500
4 radiating elements (one nifty approach would be a pair of switch
selectable horizontal dipoles at the top of each of 4 middling high posts)
PC with necessary multichannel sound card interfaces $1000
Probably $15K by the time you get it all put together. Compare that to a
big tower and a SteppIR or two and a 2kW linear. It's in the same general
ballpark.
10-15 years down the road, the potential is for small modules, costing
perhaps $500-600 each incorporating the digital stuff and a suitable 100W
or so PA, integrated with some reasonably compact radiating element. Put
10 or 15 of those modules on your roof, along a fenceline, on a pair or
three towers, etc.
>73, Dave, K1FK
>Fort Kent, ME
------------------------------
Message: 4
Date: Fri, 4 Mar 2005 20:08:58 -0500
From: "Tom Rauch" <w8ji@contesting.com>
Subject: Re: [TowerTalk] amplifiers for phased arrays
To: "Dave Bowker" <dbowker@mail.sjv.net>, <Towertalk@contesting.com>,
"Jim Lux" <jimlux@earthlink.net>
Message-ID: <000a01c5211f$ea0ab440$6501a8c0@akorn.net>
Content-Type: text/plain; charset="iso-8859-1"
> 4 SDR-1000 digital radios (w/100 Watt output) - 4@ $1300
> 4 SGC500 500W amplifiers - 4@$1200
> 4 high power computer controlled tuners 4 @ $500
> 4 radiating elements (one nifty approach would be a pair
of switch
> selectable horizontal dipoles at the top of each of 4
middling high posts)
> PC with necessary multichannel sound card interfaces $1000
Sounds like a great system if you want less significantly
than 1500 watts output, pee-poor IMD, and have time and
money to burn.
> Probably $15K by the time you get it all put together.
Compare that to a
> big tower and a SteppIR or two and a 2kW linear. It's in
the same general
> ballpark.
Except the single amp and antenna would have much better
IMD, the power would be much higher, and it would be a less
complex and less expensive system. It also would not cost
near 15K to do this with a conventional setup.
> 10-15 years down the road, the potential is for small
modules, costing
> perhaps $500-600 each incorporating the digital stuff and
a suitable 100W
> or so PA, integrated with some reasonably compact
radiating element. Put
> 10 or 15 of those modules on your roof, along a fenceline,
on a pair or
> three towers, etc.
You'd still never have 1500W power. Not unless the only
phasing you intended to use was a bi-directional pattern
with high sidelobe levels and low gain. And any compact
antennas would still be inefficient.
A simple four square with near optimum phasing has a power
division of 34%, 31%, 31%, and 4%. What does that do to the
idea of using 4 375w modules? It kills it.
You'd need three 500 watt modules and one 50 watt module.
They would also have to tolerate RF impedances varying at a
cyclic rate on the output ports without undue distortion.
Also if this fantasy array were ever built, you could NEVER
use an array with negative resistance element without
intentionally dumping (wasting) power. You also face the
severe technical problem of the amps being subjected to
power returning on the feedline due to mutual coupling from
other elements. I can easily imagine the headaches that
would cause, especially when SS PA's by themselves are awful
IMD producers!
I can't think of any advantage in using an overcomplicated
system like this in an HF application. Not one.
73 Tom
------------------------------
Message: 5
Date: Fri, 4 Mar 2005 19:08:57 -0600
From: "Merle Bone" <merlebone@charter.net>
Subject: Re: [TowerTalk] amplifiers for phased arrays
To: <towertalk@contesting.com>
Message-ID: <007d01c5211f$e8f99260$13286b18@merlebon>
Content-Type: text/plain; charset="iso-8859-1"
Jim,
Really interesting work. I was familiar with some "electronically steerable
array" stuff in the early 70's (Higher frequency). The concepts applied to
HF could have some very interesting amateur applications. Many hams don't
have a "farm" where they can put any kind of antenna they want and many
struggle with antenna restrictions. It will be very interesting to see what
capabilities might be developed from a phased array of radiators, even
within the limits of physics.
73,
Merle - W0EWM
------------------------------
Message: 6
Date: Fri, 04 Mar 2005 18:02:11 -0800
From: Jim Lux <jimlux@earthlink.net>
Subject: Re: [TowerTalk] amplifiers for phased arrays
To: "Tom Rauch" <w8ji@contesting.com>, "Dave Bowker"
<dbowker@mail.sjv.net>, <Towertalk@contesting.com>
Message-ID: <6.1.1.1.2.20050304171434.0279bab8@mail.earthlink.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 05:08 PM 3/4/2005, Tom Rauch wrote:
> > 4 SDR-1000 digital radios (w/100 Watt output) - 4@ $1300
> > 4 SGC500 500W amplifiers - 4@$1200
> > 4 high power computer controlled tuners 4 @ $500
> > 4 radiating elements (one nifty approach would be a pair
>of switch
> > selectable horizontal dipoles at the top of each of 4
>middling high posts)
> > PC with necessary multichannel sound card interfaces $1000
>
>Sounds like a great system if you want less significantly
>than 1500 watts output, pee-poor IMD, and have time and
>money to burn.
Why would you have less power with multiple amplifiers than with a single
amplifier (assuming comparable radiating elements, of whatever form)? The
"antenna loss" is mostly geometry determined, and in an apples to apples
comparison (i.e. no fair comparing a 10 foot whip on the ground against a
dipole at 100ft) the losses will be
comparable. I contend that if I were to put 3 aluminum tube dipoles at 100
ft, and drive them with 3 separate amplifiers of 500W each, the radiated
field would be comparable to that achievable with a single 1500W amplifier
driving the same 3 pieces of metal (whether coupled by a network, or by
mutual impedance).
IMD is mostly a function of what's available (off the shelf) for
amplifiers. Essentially all solid state amps run about $2/Watt, so I used
the SGC as a specific example. Most of the tube amps available in lower
powers have fairly low gain; the anti CB-linear legalities, drives design
decisions about what people sell. And, in fact, that's what prompted my
original post. I'd love to find a suitable modular amplifier for this
application that has better performance (and doesn't involve sending many
kilobucks to Amplifier Research (Model 500A100A for a mere $32K would do
nicely) http://www.amplifiers.com/post/500A100A.pdf although they don't
give any real performance specs for IMD, etc.)
> > Probably $15K by the time you get it all put together.
>Compare that to a
> > big tower and a SteppIR or two and a 2kW linear. It's in
>the same general
> > ballpark.
>
>Except the single amp and antenna would have much better
>IMD, the power would be much higher, and it would be a less
>complex and less expensive system. It also would not cost
>near 15K to do this with a conventional setup.
Less complex, yes.
Less expensive, probably.
But, the conventional set up isn't going to be, say, half as much.
> > 10-15 years down the road, the potential is for small
>modules, costing
> > perhaps $500-600 each incorporating the digital stuff and
>a suitable 100W
> > or so PA, integrated with some reasonably compact
>radiating element. Put
> > 10 or 15 of those modules on your roof, along a fenceline,
>on a pair or
> > three towers, etc.
>
>You'd still never have 1500W power. Not unless the only
>phasing you intended to use was a bi-directional pattern
>with high sidelobe levels and low gain. And any compact
>antennas would still be inefficient.
I don't think so.
In a compromise installation (the roof of a house), ANY antenna is going to
be inefficient, big, small, compact or otherwise. I contend that in such a
situation, the phased array has more potential to be useful than any single
antenna connected to a single amplifier. (you have the ability to reduce
the average reactive near field energy, so the loss due to surroundings is
less).
As far as efficiency goes, there's no requirement in amateur radio for high
"power added efficiency". Worrying about efficiency is only because you
have a "max power to the feedline" regulatory limitation, and you'd like to
radiate as much of that as possible.
All that matters is the power to the feedline(s), and in the case of an
amplifier where the radiating element is part of a resonant circuit in the
amplifier, one can make a case that IR losses in the antenna shouldn't be
counted against your 1500 PEP (any more than IR losses in the plate circuit
of a conventional amplifier should be counted). The regulatory precedent
is in things like cell phones, garage door transmiters, RFID systems, and
the like, many of which use components in the final amplifier as the
radiating element (to reduce cost)). Near field losses are a bit more
dicey in a regulatory sense.
I don't think I'd ever claim that an antenna (of whatever kind) 10 ft off
the ground is going to be competitive with an antenna 100 ft off the
ground. However, there are large areas of the country, with lots of hams
(and potential hams) who cannot put up a 100 ft high antenna, but CAN put
up a 10 or 20 ft high antenna, particularly if it's visually inconspicuous.
The phased array approach provides a way, when constrained by such
restrictions and circumstances, to get more performance. Sure, it's
expensive (today). Sure, it's complex (today). Both of those could change
in the future. Maybe not. Maybe the only future for hams is for those who
live on 10 acres with accomodating neighbors. One thing is certain,
though. There WILL be more installation restrictions on ham
antennas. There WILL be more environmental RF noise to deal with. If you
want to operate on HF, new approaches are needed. I won't say that phased
arrays (whether amplifier per element or not) using insitu calibration are
the panacea, however, it seems that working on this approach is as useful
for keeping HF operation alive as any other activity.
>A simple four square with near optimum phasing has a power
>division of 34%, 31%, 31%, and 4%. What does that do to the
>idea of using 4 375w modules? It kills it.
"near optimum" by what criterion? Forward gain? Radiated field strength in
the desired direction? Have you attempted to find a phasing which radiates
375W from each element? How much worse (if at all) is this than what you
give?
The "simple 4 square" also isn't a good model for the kinds of installation
I'm aiming at. Unevenly spaced elements. Interacting objectes in the near
field.
When you start to throw non-ideal locations and installations into the mix,
the "penalty" from constraining the optimization to "equal power per
element" isn't all that great.
>You'd need three 500 watt modules and one 50 watt module.
>They would also have to tolerate RF impedances varying at a
>cyclic rate on the output ports without undue distortion.
Why would the impedance be varying? The frequency is constant. The phasing
is constant. The mutual impedances are constant. No cyclical variation to
be seen (except when you scan the array, but that's another story).
>Also if this fantasy array were ever built, you could NEVER
>use an array with negative resistance element without
>intentionally dumping (wasting) power.
This is true. The real question is whether you can always find a phasing
that doesn't have negative power. This isn't something that can be easily
answered analytically (except in trivial cases..)
> You also face the
>severe technical problem of the amps being subjected to
>power returning on the feedline due to mutual coupling from
>other elements.
Clearly, one needs to supply reactive power to each element (i.e. you need
a tuning network of some sort).
>I can easily imagine the headaches that
>would cause, especially when SS PA's by themselves are awful
>IMD producers!
>
>I can't think of any advantage in using an overcomplicated
>system like this in an HF application. Not one.
Constrained environments are your advantage.
Jim, W6RMK
------------------------------
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End of TowerTalk Digest, Vol 27, Issue 16
*****************************************
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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