Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

I need an auto-tuner that I can control from a laptop, and set frequencies
as needed (mostly for ALE). I can do the digital design and the software
in my sleep, for an embedded microprocessor that can control all of that,
but the heavy-lifting part of the antenna tuner (all the toroids and caps
and relays) is a bit beyond my capabilities.

If there are any construction articles that I can adapt to my needs that
would be a very big help.

Thanks...

Rick (W-A-one-R-K-T) wrote:
Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

I need an auto-tuner that I can control from a laptop, and set frequencies
as needed (mostly for ALE). I can do the digital design and the software
in my sleep, for an embedded microprocessor that can control all of that,
but the heavy-lifting part of the antenna tuner (all the toroids and caps
and relays) is a bit beyond my capabilities.

If there are any construction articles that I can adapt to my needs that
would be a very big help.

Thanks...


The original LDG tuner was described in a construction article in QST,
including a schematic. The SGC manuals have the schematic in them.

Practically speaking, it's just a bunch of relays. The hard part is
finding suitable relays. The LDG uses a L network with the capacitor
switched either to the input or output and inductors wound on toroid
cores. The SGC uses a pi network, and closewound air core inductors.

The values are in an approximate powers of two sequence (allowing for
standard values and the fact that you only get integer numbers of turns)
Capacitors in the AT11: 5,10,20,39,82,160,320,640 pF
Inductors in the AT11: 0.11, 0.22, 0.39, 0.59, 1.25, 2.5, 5, 10 uH


how much power are you going to run and what's the maximum mismatch?
that determines the size of the wire in the inductors and the
current/voltage ratings of the capacitors.
You also want to decide if you want latching or non-latching relays.
Most modern tuners use latching relays because after tuning, you want
power to be reduced to a minimum. For ALE, this might not be as big a deal.

Most modern tuners also implement some sort of frequency counter, which
is then used for a lookup table to find a previously set configuration.

Another key design aspect is that you probably want to shut down the
microprocessor after tuning, so that you don't have spurious signals
from the microprocessor clock. Either that, or choose a clock frequency
where the harmonics don't fall in *bad* places.

I've gone through the design and build exercise several times. Unless
you're doing it for the experience of designing an autotuner, I suspect
that buying a ready made tuner like the LDG AT200PC, which has a RS232
interface, is probably the cheapest and easiest solution. It has a
published control protocol which is easy to work with (except that you
need to be able to generate a pulse on RTS to wake it up...).


Jim, W6RMK

In article ,
Rick (W-A-one-R-K-T) wrote:

Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

I need an auto-tuner that I can control from a laptop, and set frequencies
as needed (mostly for ALE). I can do the digital design and the software
in my sleep, for an embedded microprocessor that can control all of that,
but the heavy-lifting part of the antenna tuner (all the toroids and caps
and relays) is a bit beyond my capabilities.

If there are any construction articles that I can adapt to my needs that
would be a very big help.

There was a two-part (I think) article in QST a couple of years ago
which showed a high-power external ATU with onboard microprocessor
control.

Its design was rather different from the LDG/SGC/Sunair/what-have-you
microprocessor-controlled switched-cap/inductor pi/L tuner. It
uses air-variable capacitors and a roller inductor (in a fairly
typical T-network). It doesn't implement automatic search-and-match.
Instead, it tunes from memory. You tune your radio to a specific
frequency, adjust the caps and inductor for the desired match using
up/down toggle switches, and then hit a "memorize" button, and the
controller remembers the frequency and the correct reactance settings.
On subsequent frequency changes, you just select the desired frequency
and the correct reactances are "dialed in".

Eliminating the "try lots of combinations to achieve the lowest SWR"
part of the system will greatly simplify the RF part of the
implementation... you won't need to implement the voltage and current
detectors, phase comparators, etc. needed to permit the digital logic
to measure SWR, etc. The on-board digital logic might be something as
simple as a micro which can [1] run a set of three stepper or gearhead
motors to rotate the cap and inductor shafts, and [2] read out DC
voltages from a set of potentiometers connected to the shafts.

A simple serial-port or USB protocol would then allow the PC to
determine the current settings of the reactances, and control the
motors to adjust them as needed for a new frequency. A second serial
or USB port would be used to communicate with whatever your rig is, to
either read out the frequencies being tuned, or to switch the rig to a
different frequency.

A similar system could be done with switched banks of inductors and
caps, in the usual power-of-two size hierarchy. In this case, the
micro would be just ordered to turn on or off the various relays used
to switch toroids and caps in and out of the series and shunt circuits.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
In article ,
Rick (W-A-one-R-K-T) wrote:


Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

I need an auto-tuner that I can control from a laptop, and set frequencies
as needed (mostly for ALE). I can do the digital design and the software
in my sleep, for an embedded microprocessor that can control all of that,
but the heavy-lifting part of the antenna tuner (all the toroids and caps
and relays) is a bit beyond my capabilities.

If there are any construction articles that I can adapt to my needs that
would be a very big help.


There was a two-part (I think) article in QST a couple of years ago
which showed a high-power external ATU with onboard microprocessor
control.

Its design was rather different from the LDG/SGC/Sunair/what-have-you
microprocessor-controlled switched-cap/inductor pi/L tuner. It
uses air-variable capacitors and a roller inductor (in a fairly
typical T-network).

This was an interesting approach (and I believe parts of it are sold as
a kit or assembled device, too). It would be a good approach for a
one-off, but if are going to do more than one of them, implying that you
need to get all the parts new (as opposed to scrounging surplus), it
gets pretty expensive pretty quick. (fiddling around to work out
mechanical details to use what's in your junk box and at the surplus
store is fine, when you build one.. gets pretty tedious if you want to
build 8)

It also might not tune fast enough for some ALE type applications or
have sufficient resolution.

Consider a switched relay scheme with 8 relays for L and 8 for C..
you've got 256 possible values. With a standard air variable C driven
by a motor, you'd need some sort of reduction gearing to get the ability
to set the plates to better than 1 degree accuracy. You could use a
stepper or a dc motor with an encoder, but you're still limited in the
speed at which you can go from one setting to another (I'd guess a
couple seconds... fast compared to cranking knobs yourself, slow
compared to 10-20 milliseconds for a relay). The roller inductor has
reduction gearing essentially built in, but, again, you're not going to
be spinning it at 3600 RPM.. Probably more like 60 or 120 RPM (2 knob
turns per second is pretty quick). Vacuum variables are more like the
roller inductor (many turns to span the capacitance range). Jennings
does life testing with 50-75% stroke at 200-300 rpm... at that speed, a
cap that takes 10 turns from end to end could do 20-30 strokes per
minute, or a complete stroke in 3 seconds or so.


Eliminating the "try lots of combinations to achieve the lowest SWR"
part of the system will greatly simplify the RF part of the
implementation... you won't need to implement the voltage and current
detectors, phase comparators, etc. needed to permit the digital logic
to measure SWR, etc. The on-board digital logic might be something as
simple as a micro which can [1] run a set of three stepper or gearhead
motors to rotate the cap and inductor shafts, and [2] read out DC
voltages from a set of potentiometers connected to the shafts.


An ordinary pot hooked to the shaft probably won't do as a feedback
device. a) resolution issues, b) life... Typical panel pots have lives
in the million moves range, which seems like a lot, until you do
scanning 24/7 with a move every couple seconds.. say 20,000 moves/day
will burn through a million moves in less than 2 months. Their
resistance vs position will also change over life (you don't notice this
on a volume control). There are feedback pots designed for this kind of
duty that have much longer lives and have high quality resistive
elements and wipers, but they aren't cheap. You'd probably want to use
a shaft encoder (and incremental shaft encoders with 1000 pulses/rev are
easy to come by).


Any way you look at it, there's a fair amount of electromechanical
engineering that goes into making a reliable system like this (which is
why the commercial units are fairly expensive..It's not just because
they're connected to multi $100K plasma etchers.). In the classic
antenna tuner case, it's a bit easier, because you don't need high
quality initial position, just get close enough, and home in on the
optimum setting for the match.


A simple serial-port or USB protocol would then allow the PC to
determine the current settings of the reactances, and control the
motors to adjust them as needed for a new frequency. A second serial
or USB port would be used to communicate with whatever your rig is, to
either read out the frequencies being tuned, or to switch the rig to a
different frequency.

A similar system could be done with switched banks of inductors and
caps, in the usual power-of-two size hierarchy. In this case, the
micro would be just ordered to turn on or off the various relays used
to switch toroids and caps in and out of the series and shunt circuits.


Which is essentially what something like the LDG AT200PC is..

Rick (W-A-one-R-K-T) wrote:
Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

http://www.miami.muohio.edu/presiden.../ezhistory.htm
http://www.somis.org/bbat.html

--
HZ

Hank Zoeller wrote:
Rick (W-A-one-R-K-T) wrote:

Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?


http://www.miami.muohio.edu/presiden.../ezhistory.htm

That's the stepper motor controlled one.. Note that he used a switch to
switch between fixed inductors rather than a roller inductor. Also note
the comment about 3 months of evenings and weekends to build it.


http://www.somis.org/bbat.html

On 6 Aug, 16:09, Jim Lux wrote:
Hank Zoeller wrote:
Rick (W-A-one-R-K-T) wrote:

Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

http://www.miami.muohio.edu/presiden...uner/ezhistory...

That's the stepper motor controlled one.. Note that he used a switch to
switch between fixed inductors rather than a roller inductor. Also note
the comment about 3 months of evenings and weekends to build it.



http://www.somis.org/bbat.html- Hide quoted text -

- Show quoted text -

Why not make a duplicate tuner of that which is in your radio now
except use
higher power units. You should be able to control this unit using the
existing
circuitry in the radio. Actually a purchased toroid transformer with
several taps would
probably the quickest way to go using a multipole switch.
Art

In article ,
Jim Lux wrote:

An ordinary pot hooked to the shaft probably won't do as a feedback
device. a) resolution issues, b) life... Typical panel pots have lives
in the million moves range, which seems like a lot, until you do
scanning 24/7 with a move every couple seconds.. say 20,000 moves/day
will burn through a million moves in less than 2 months. Their
resistance vs position will also change over life (you don't notice this
on a volume control). There are feedback pots designed for this kind of
duty that have much longer lives and have high quality resistive
elements and wipers, but they aren't cheap. You'd probably want to use
a shaft encoder (and incremental shaft encoders with 1000 pulses/rev are
easy to come by).

Any way you look at it, there's a fair amount of electromechanical
engineering that goes into making a reliable system like this (which is
why the commercial units are fairly expensive..It's not just because
they're connected to multi $100K plasma etchers.). In the classic
antenna tuner case, it's a bit easier, because you don't need high
quality initial position, just get close enough, and home in on the
optimum setting for the match.

Good points!

A couple of years ago, I was at a local hamfest/fleamarket, digging
through a big pile of relatively-new-looking industrial surplus. I
came across a nice air-variable capacitor, and asked the seller for a
price... got it for around $5, I think. He then said "Oh, if you like
those, I think there's one of them inside one of these things... that
one there." Metal case, N connector on one side, high-voltage
connector on the other, and a DB-25 for some sort of control connection.

I offered him $15 and he accepted.

After looking at it for a while, and doing some research, I've
concluded that it's just what you indicate - a matching unit for a
single-frequency RF plasma-etching system. It has what appears to be
a fairly spiffy SWR detector, and then an L-match network designed to
match a 50-ohm (I assume) RF feed to a lower-impedance load having
some amount of reactance. The shunt element is an air-variable cap.
The series element is another air-variable cap, in series with a hefty
silver-plated coil which feeds the high-voltage connector. These are
big cheese-cutter caps with widely-spaced plates. I get the feeling
that this matcher was handling quite a lot of power.

Both air-variable caps are turned via geared-down DC motors, and have
position-sensing pots. The motors, pots, and SWR detector are all
hooked to the DB-25, and I assume that in normal operation there was a
control console of some sort at the other end of the cable which had
the necessary control logic.

I haven't been able out a way to make real use of it yet, but it's a
glorious beast to look at, and I don't think I want to know what it
probably cost when it was new.

As to the original query - I suspect that an important part of the
practical engineering of an ATU of this sort, is enabling the digital
logic to co-exist well with the RF. Not only do you need to keep
birdies from the micro out of the RF path (by e.g. idling the
processor when not tuning), you also have to keep induced RF on the
control and sensing lines from sneaking into the digital logic and
causing it to either malfunction, crash entirely, or spew Magic Blue
Smoke out of its poor little fried-CMOS brains :-)

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Rick (W-A-one-R-K-T)" wrote in message
news

Are there any construction articles around anywhere that describe an
auto-tuner similar to the LDG and SGC offerings?

I need an auto-tuner that I can control from a laptop, and set frequencies
as needed (mostly for ALE). I can do the digital design and the software
in my sleep, for an embedded microprocessor that can control all of that,
but the heavy-lifting part of the antenna tuner (all the toroids and caps
and relays) is a bit beyond my capabilities.

If there are any construction articles that I can adapt to my needs that
would be a very big help.

Thanks...


ive seen more than a few auto tuners that had lightnig damage to just the
processor that can be had at hamfest. This should supply the caps inductors
and relays you need.