Topics

Standard Air Variable (not butterfly) for new 40m loop


Doug Wood
 

Hello all,
        my first loop is an  80 meter loop ,Vacuum Variable Cap using Lofture's MLC.
The one i just built is a 40m ML with an standard air variable cap , not a butterfly shape. (continuous rotation no end stops )

I have been setting up ( Loftur's  MLC) and noticed the tuning is not smooth tiny incremental changed in frequency 
It seems to jump 20-30 khz at a time. I'm using  a standard inexpensive stepper motor with aprox 200 steps / revolution.
I think the stepper may be incrementing more than one step .

 I have the stepper settings as follows.
Max rate as slow rpm as possible ( 30 Rpm)
Variable rate : No speed up.
Micro steps set to 0 (zero)

      It looks like the tuning isn't fine enough ?

Any help would be greatly appreciated.

           Doug      VE3GVW





Leonard A. Gucciardo KD2NEN
 

I had the same problem using an air variable capacitor. The only capacitor that I found that works is a dual gang capacitor putting the stators in series. The movable plates then pass between the stator plates and provide a consistent capacitance. Air variables have a wiper that changes resistance thru the rotation of the shaft. The resistance is never consistent. This changes the tuned frequency every rotation. No good for this setup. Bear in mind that the capacitance in series reduces the capacity of the variable cap to 1/2. So if you get a 2 stator cap with 2 sections each 500pf your total capacitance will be 250pf. Also the voltage handling will double so if the capacitor is rated at 1kv you can put 2kv into it. Also try using a 100 to 1 planetary gear ratio stepper with an air capacitor. It will give you a resolution of .018 degrees per step which is perfect for air variable capacitors. 

Leonard A. Gucciardo
KD2NEN

On Feb 10, 2021, at 10:09 AM, Doug Wood <whitbypilot@...> wrote:

Hello all,
        my first loop is an  80 meter loop ,Vacuum Variable Cap using Lofture's MLC.
The one i just built is a 40m ML with an standard air variable cap , not a butterfly shape. (continuous rotation no end stops )

I have been setting up ( Loftur's  MLC) and noticed the tuning is not smooth tiny incremental changed in frequency 
It seems to jump 20-30 khz at a time. I'm using  a standard inexpensive stepper motor with aprox 200 steps / revolution.
I think the stepper may be incrementing more than one step .

 I have the stepper settings as follows.
Max rate as slow rpm as possible ( 30 Rpm)
Variable rate : No speed up.
Micro steps set to 0 (zero)

      It looks like the tuning isn't fine enough ?

Any help would be greatly appreciated.

           Doug      VE3GVW





--
LennyG KD2NEN


Immo
 

hi Dough,
use a geared Stepper, 1:19. Than you would get sufficient resolution (abt 1.5kc)
73, Immo DL5KB


2E0IDE@...
 

Hi Doug

 

I have a loop with an air cap and it is driven by a  stepper with 100:1 reduction gearbox. It works very well. If your stepper does not have a reduction gearbox then this may be the issue.

 

Barry – 2E0IDE

 

From: loopController@groups.io <loopController@groups.io> On Behalf Of Doug Wood
Sent: 10 February 2021 15:10
To: loopController@groups.io
Subject: [loopController] Standard Air Variable (not butterfly) for new 40m loop

 

Hello all,
        my first loop is an  80 meter loop ,Vacuum Variable Cap using Lofture's MLC.
The one i just built is a 40m ML with an standard air variable cap , not a butterfly shape. (continuous rotation no end stops )

I have been setting up ( Loftur's  MLC) and noticed the tuning is not smooth tiny incremental changed in frequency 
It seems to jump 20-30 khz at a time. I'm using  a standard inexpensive stepper motor with aprox 200 steps / revolution.
I think the stepper may be incrementing more than one step .

 I have the stepper settings as follows.
Max rate as slow rpm as possible ( 30 Rpm)
Variable rate : No speed up.
Micro steps set to 0 (zero)

      It looks like the tuning isn't fine enough ?

Any help would be greatly appreciated.

           Doug      VE3GVW




Virus-free. www.avast.com


Rene Heon
 

Doug,

I Have a 300 X reduction stepping motor that is gathering dust in my shack.
It is the motor on the right hand illustration on the above page.
I bought it years ago for my loop but then I used a vacuum variable capacitor with another motor.

I will gladly mail you the motor. I found your city and postal code on a hamcall lookup site. I only need your street address.
I am confined to the house and will ask my children to handle the mailing when they stop by in the weekend.
You should receive the motor in a couple of weeks
Cordially,

René VE2MPA


On Feb 10, 2021, at 10:09 AM, Doug Wood <whitbypilot@...> wrote:

Hello all,
        my first loop is an  80 meter loop ,Vacuum Variable Cap using Lofture's MLC.
The one i just built is a 40m ML with an standard air variable cap , not a butterfly shape. (continuous rotation no end stops )

I have been setting up ( Loftur's  MLC) and noticed the tuning is not smooth tiny incremental changed in frequency 
It seems to jump 20-30 khz at a time. I'm using  a standard inexpensive stepper motor with aprox 200 steps / revolution.
I think the stepper may be incrementing more than one step .

 I have the stepper settings as follows.
Max rate as slow rpm as possible ( 30 Rpm)
Variable rate : No speed up.
Micro steps set to 0 (zero)

      It looks like the tuning isn't fine enough ?

Any help would be greatly appreciated.

           Doug      VE3GVW






Doug Wood
 

Rene,
     Thankyou for your generous offer.
 My address is good on QRZ . My call is VE3GVW 
    The Address is           402-1875 Glenanna Road
                                             Pickering, Ontario
                                                      L1V3V6


Doug Wood
 
Edited

Hi Rene,
          The package has arrived . 
               Thankyou very much. It will be put to good use.

                        Doug  VE3GVW