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Old October 8th 05, 07:26 AM
Lee
 
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Default Re Magnetic Loop !!!

To continue the saga......

I fitted a variable capacitor to my 10 foot circumference 1mtr loop and am
able to tune 80 to almost 15 meters...works well..but.........

How to fit a motor drive !!!.....there seems to be nowhere to acquire cogs,
pulleys or gear sets....no model shops around that carries components, that
i`ve googled for anyway..(now when i were a lad! ).... ;-)

Can you imagine how fast that electric motor turns the capacitor, even with
reduced voltage???..you have to be quick i can tell you or you miss the
sweet spot heh,heh....

Seriously, any ideas to slow the tuning rate will be most welcome .

Thanks.

Lee......G6ZSG.....



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Old October 8th 05, 08:30 AM
Richard Clark
 
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On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:
Seriously, any ideas to slow the tuning rate will be most welcome .


Hi Lee,

Use the old stand-by of the screwdriver antennas, a screwdriver motor.

However, I expect you want two speed - then try a variable speed
battery powered drill.

For fine resolution and high speed both, look into the world of
Stepper motors. You can even design for calibrated settings instead
of hunting - or rough position indicators.

73's
Richard Clark, KB7QHC
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Old October 8th 05, 09:05 AM
Lee
 
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Default


"Richard Clark" wrote in message
...
On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:
Seriously, any ideas to slow the tuning rate will be most welcome .


Hi Lee,

Use the old stand-by of the screwdriver antennas, a screwdriver motor.


Tried that, it has far to much torque even on low volts .... damaged the
gearing on my spare cap :-/

However, I expect you want two speed - then try a variable speed
battery powered drill.


Good idea, worth looking into!!

For fine resolution and high speed both, look into the world of
Stepper motors. You can even design for calibrated settings instead
of hunting - or rough position indicators.


I`ll do a google for steppermotors .... thanks.

Lee.....G6ZSG....


73's
Richard Clark, KB7QHC



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Old October 8th 05, 09:14 AM
Ian White G/GM3SEK
 
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Default

Lee wrote:
To continue the saga......

I fitted a variable capacitor to my 10 foot circumference 1mtr loop and am
able to tune 80 to almost 15 meters...works well..but.........

How to fit a motor drive !!!.....there seems to be nowhere to acquire cogs,
pulleys or gear sets....no model shops around that carries components, that
i`ve googled for anyway..(now when i were a lad! ).... ;-)

Can you imagine how fast that electric motor turns the capacitor, even with
reduced voltage???..you have to be quick i can tell you or you miss the
sweet spot heh,heh....

Seriously, any ideas to slow the tuning rate will be most welcome .


Lots of model-making and robotics suppliers in the UK have small
plastic gearboxes, plastic shafts, couplers etc. Try some of the links
from my "Components and Suppliers" page.

As a short-cut, try to find a small battery-powered barbecue spit motor
at one of the home and leisure stores (probably in the end-of-season
bargain bin). They are still a bit fast, but will run at reduced voltage
or with pulse-width control to slow them down.


--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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Old October 8th 05, 09:16 AM
Richard Clark
 
Posts: n/a
Default

On Sat, 08 Oct 2005 08:05:35 GMT, "Lee"
wrote:

Use the old stand-by of the screwdriver antennas, a screwdriver motor.


Tried that, it has far to much torque even on low volts .... damaged the
gearing on my spare cap :-/


Hi Lee,

One way to control that, at least speed-wise, is to turn the DC
voltage into pulse-width modulated voltage. You are always applying
the same voltage, but you turn it on for a short-to-long time, and off
for a long-to-short time over any interval. You change the speed by
changing these times. This is more properly called Dwell Time.

This offers the prospects of maintaining a constant torque over a
considerable range of speed. I'm not certain by what you mean about
"too much torque," unless you have too much resistance for the gears
to drive.... Stepper motors are also noted for high torque - it goes
with the turf.

73's
Richard Clark, KB7QHC


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Old October 8th 05, 10:00 AM
Owen Duffy
 
Posts: n/a
Default

On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:

To continue the saga......

I fitted a variable capacitor to my 10 foot circumference 1mtr loop and am
able to tune 80 to almost 15 meters...works well..but.........

How to fit a motor drive !!!.....there seems to be nowhere to acquire cogs,
pulleys or gear sets....no model shops around that carries components, that
i`ve googled for anyway..(now when i were a lad! ).... ;-)

Can you imagine how fast that electric motor turns the capacitor, even with
reduced voltage???..you have to be quick i can tell you or you miss the
sweet spot heh,heh....

Seriously, any ideas to slow the tuning rate will be most welcome .


Assuming it is a permag motor, reduce the motor voltage... add a
current limited driver to limit the torque, an electronic shear pin if
you like... except it doesn't shear.

I am assuming that you are trying to tune the reactance out, to
achieve an acceptable VSWR on the line to the ATU/transceiver. Have
you considered automating the capacitor drive. You could build a phase
detector (between V and I at the antenna input) as a sensor to control
the motor drive.

Owen
--
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Old October 8th 05, 12:30 PM
Adelphia
 
Posts: n/a
Default

Here in the USA ALL Electronics had 12volt 6RPM DC motors. I drive my large
4600v variable with it using a DC pulse width motor speed control. The motor
control was around $22 as a kit in the USA. I would actually like about 3RPM
since the motor control slow speed needed for fine tuning is in a small
range. I could gear it but a mechanical mess. A simple DPDT switch is used
to reverse direction.

Check your electronic parts dealers to see if they have motor with built-in
gear boxes. Best way to do it.

Dick N3HKN
PS: My loop is 1 meter on a side square and is used on 20 meters in the
attic. I have set it outside where the noise level is less but on really
cold days the motor will not turn. Used a simple plastic container from a
local discount store. I'll stick to the attic since I have a GAP vertical as
well. Yes, they are comparable given the dipole like pattern of the loop.


"Owen Duffy" wrote in message
...
On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:

To continue the saga......

I fitted a variable capacitor to my 10 foot circumference 1mtr loop and am
able to tune 80 to almost 15 meters...works well..but.........

How to fit a motor drive !!!.....there seems to be nowhere to acquire
cogs,
pulleys or gear sets....no model shops around that carries components,
that
i`ve googled for anyway..(now when i were a lad! ).... ;-)

Can you imagine how fast that electric motor turns the capacitor, even
with
reduced voltage???..you have to be quick i can tell you or you miss the
sweet spot heh,heh....

Seriously, any ideas to slow the tuning rate will be most welcome .


Assuming it is a permag motor, reduce the motor voltage... add a
current limited driver to limit the torque, an electronic shear pin if
you like... except it doesn't shear.

I am assuming that you are trying to tune the reactance out, to
achieve an acceptable VSWR on the line to the ATU/transceiver. Have
you considered automating the capacitor drive. You could build a phase
detector (between V and I at the antenna input) as a sensor to control
the motor drive.

Owen
--



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Old October 8th 05, 01:50 PM
Lee
 
Posts: n/a
Default


"Richard Clark" wrote in message
...
On Sat, 08 Oct 2005 08:05:35 GMT, "Lee"
wrote:

Use the old stand-by of the screwdriver antennas, a screwdriver motor.


Tried that, it has far to much torque even on low volts .... damaged the
gearing on my spare cap :-/


Hi Lee,

One way to control that, at least speed-wise, is to turn the DC
voltage into pulse-width modulated voltage. You are always applying
the same voltage, but you turn it on for a short-to-long time, and off
for a long-to-short time over any interval. You change the speed by
changing these times. This is more properly called Dwell Time.


Yes, i`ve been looking into that and it seems the best way to go, a local
supplier has a panel mount version in stock 15.00 ($16.00??)......so!!.

This offers the prospects of maintaining a constant torque over a
considerable range of speed. I'm not certain by what you mean about
"too much torque," unless you have too much resistance for the gears
to drive....


Not enough resistance, the capacitor comes to the end of its travel but the
torque wants to continue..... hence the damage to my spare capacitor!!!.

Regards.

Lee...G6ZSG......

73's
Richard Clark, KB7QHC



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Old October 8th 05, 01:53 PM
Lee
 
Posts: n/a
Default


"Owen Duffy" wrote in message
...
On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:

To continue the saga......

I fitted a variable capacitor to my 10 foot circumference 1mtr loop and

am
able to tune 80 to almost 15 meters...works well..but.........

How to fit a motor drive !!!.....there seems to be nowhere to acquire

cogs,
pulleys or gear sets....no model shops around that carries components,

that
i`ve googled for anyway..(now when i were a lad! ).... ;-)

Can you imagine how fast that electric motor turns the capacitor, even

with
reduced voltage???..you have to be quick i can tell you or you miss the
sweet spot heh,heh....

Seriously, any ideas to slow the tuning rate will be most welcome .


Assuming it is a permag motor, reduce the motor voltage... add a
current limited driver to limit the torque, an electronic shear pin if
you like... except it doesn't shear.

I am assuming that you are trying to tune the reactance out, to
achieve an acceptable VSWR on the line to the ATU/transceiver. Have
you considered automating the capacitor drive. You could build a phase
detector (between V and I at the antenna input) as a sensor to control
the motor drive.


Doesn`t work with a magloop!!!.....thanks anyway.

Lee.....G6ZSG.....


Owen
--



  #10   Report Post  
Old October 8th 05, 01:58 PM
Lee
 
Posts: n/a
Default


"Adelphia" wrote in message
...
Here in the USA ALL Electronics had 12volt 6RPM DC motors. I drive my

large
4600v variable with it using a DC pulse width motor speed control. The

motor
control was around $22 as a kit in the USA. I would actually like about

3RPM
since the motor control slow speed needed for fine tuning is in a small
range. I could gear it but a mechanical mess. A simple DPDT switch is used
to reverse direction.

Check your electronic parts dealers to see if they have motor with

built-in
gear boxes. Best way to do it.


Yes, thanks Lee....G6ZSG......


Dick N3HKN
PS: My loop is 1 meter on a side square and is used on 20 meters in the
attic. I have set it outside where the noise level is less but on really
cold days the motor will not turn. Used a simple plastic container from a
local discount store. I'll stick to the attic since I have a GAP vertical

as
well. Yes, they are comparable given the dipole like pattern of the loop.





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