Coupling Shaft.


James Holohan
 

Just wondering if it is absolutely necessary to insulate the VVC shaft from the stepper motor shaft?


Patrick
 

It's to avoid charging the stepper motor with RF and potentially creating RF inductance between the motor and the motor's circuits and any other circuits in the electrical path such as the controller.
If the motor was connected to the antenna it becomes part of the antenna, isolating it disconnects it electrically from the antenna.
At least that's my limited understanding.


Immo, DL5KB
 
Edited

Hi James,
if you do use your loop only for receiving, you might couple it direct to the stepper (result is a little degrading of possible receiving quality).

If you like to transmit with your loop, you should regard, that you drive a high Q LC-resonator. The voltage across the capacitor can reach some 1.000 V (i.E. abt. 3.000 V while driving with 100W). The axle of the capacitor is electrical connected to one plate of the capacitor, so you have high voltage of high frequency on this axle, while transmitting. (see my posts )  If your stepper's housing is not connected to neutral/ earth, he will also get high tension RF. From housing to the windings of stepper there is no great insulation for RF (capacitive connection). So you will get not predictable effects to your controller.

If you connect your stepper's housing to earth, your loop will be not tunable.

So, please, for best results ever use an isolating piece (resisting the expected voltages) of axle between capacitor and stepper! 

73, Immo, DL5KB


James Holohan
 

Many thanks Immo for the sound explanation. I will implement the required isolation.

Best 73’s.

Jim EI4HH.

 

Sent from Mail for Windows

 

From: Immo, DL5KB
Sent: Thursday 1 September 2022 14:48
To: loopController@groups.io
Subject: Re: [loopController] Coupling Shaft.

 

[Edited Message Follows]
[Reason: isolating piece (not peace!) surely peace to all friends :-)]

Hi James,
if you do use your loop only for receiving, you might couple it direct to the stepper (result is a little degrading of possible receiving quality).

If you like to transmit with your loop, you should regard, that you drive a high Q LC-resonator. The voltage across the capacitor can reach some 1.000 V (i.E. abt. 3.000 V while driving with 100W). The axle of the capacitor is electrical connected to one plate of the capacitor, so you have high voltage of high frequency on this axle, while transmitting. (see my posts )  If your stepper's housing is not connected to neutral/ earth, he will also get high tension RF. From housing to the windings of stepper there is no great insulation for RF (capacitive connection). So you will get not predictable effects to your controller.

If you connect your stepper's housing to earth, your loop will be not tunable.

So, please, for best results ever use an isolating piece (resisting the expected voltages) of axle between capacitor and stepper! 

73, Immo, DL5KB

 


Gill
 

I don’t think so.  MFJ may sell more mag loops than anybody, and they don’t use an insulated shaft.


Immo, DL5KB
 

hi Gill,

I know why! They don‘t use VVC‘s

73, DL5KB 


Patrick
 

Interesting, which antenna is this?


Immo, DL5KB
 
Edited

hi Patrick,

look at webpage of mfj… But they don‘t have such a comfortable way of tuning…  abt 450$ a piece.

73


Patrick
 

Found it... https://www.youtube.com/watch?v=xHVkqz3T_l8

The capacitor could be being used to filter the RF and keep it out of the wire but I'm not an engineer, this is only a thought.



Patrick
 

Noticed that and definitely not cheap and affordable.

I'd say that while this group has the best tuners out there they are not the simplest tuners and require some work to get going.


Allen Hill
 

If it is a Transmitting Loop the voltages on the capacitor plates can be in the hundreds to thousands of volts depending in TX power. This requires isolation somewhere in the system least a shock (or worse) will occur. Of course this only occurs during TX.

This isolation can be done in a number of ways. The capacitor shaft may be a non conductive material. If it is a manual tune loop the knob connected to the shaft may be non-conductive. If it is a motor tuned system typically a non-conductive coupler ties the capacitor shaft to the drive. But somewhere the isolation exists in a Transmitting Loop.

73
Allen Hill
KI4QCK



On September 8, 2022, at 8:13 AM, Gill <w4bxa@...> wrote:


I don’t think so.  MFJ may sell more mag loops than anybody, and they don’t use an insulated shaft.


Immo, DL5KB
 

Hi all,
 
Why does the axle of a VVC needs to be isolated and that of a Butterfly-C not?
 
I think it would be going too far to describe the electrical states during operation using mathematical formulas at this point. I'll try to do that with a few drawings and a more simple explanation.
 
If tuned, a mag-loop is a parallel resonant circuit. Let's start with the capacitor. The states on the capacitor change from charged positive to zero and then to charged negative. These states alternate in the form of a sine wave in time with the resonant frequency.
 
The charge on the capacitor generates a current in the parallel inductance (loop) until the capacitor is completely discharged. When the capacitor is discharged, all of the energy is stored in the inductor's magnetic field.
 
The magnetic field now generates a current in the opposite direction and thus charges the capacitor again, but with reversed polarity. Losses that occur are compensated by supplying energy. In this way, the oscillation is maintained. A part of the magnetic field is also radiated. The loop "sends".
 
Now to the starting question:
The difference is caused by the design of the capacitors.
 
The VVC is a two-electrode unit. The resonant voltage of the oscillating circuit is always present at the electrodes, alternating between positive and negative. The drive axle is electrically connected to one of the capacitor plates. So there is the full high voltage during operation. The electrical zero point of the loop is the mechanical middle of the loop.

 
The Butterfly-C consists of two capacitors connected in series. The inner plates are like a third electrode in the middle of the capacitor. The drive axle is connected to this. The voltage at this point is almost zero, as result of the addition of the outer voltages. The outer electrodes oscillate in terms of voltage around this midpoint. This is why you can attach the axle here without insulation. However, some differences in the two capacitors (synchronism) can also cause small voltages (a few volts) to occur. An isolation of the axle is recommanded but not essential.
 
 
73, Immo


Allen Hill
 

Hi Immo, I think you have explained the issues perfectly.

I think it's important that users are aware of the mechanical makeup of capacitors used in Transmitting Loops. I've seen a number of loops built with plate capacitors that are not of the butterfly style. Depending on the mechanical methods used in the capacitor a large potential can be present on the shaft (during TX).

Thanks for helping to add clarity to this issue!

73
Allen Hill
KI4QCK



On September 9, 2022, at 12:52 PM, "Immo, DL5KB" <dl5kb@...> wrote:


Hi all,
 
Why does the axle of a VVC needs to be isolated and that of a Butterfly-C not?
 
I think it would be going too far to describe the electrical states during operation using mathematical formulas at this point. I'll try to do that with a few drawings and a more simple explanation.
 
If tuned, a mag-loop is a parallel resonant circuit. Let's start with the capacitor. The states on the capacitor change from charged positive to zero and then to charged negative. These states alternate in the form of a sine wave in time with the resonant frequency.
 
The charge on the capacitor generates a current in the parallel inductance (loop) until the capacitor is completely discharged. When the capacitor is discharged, all of the energy is stored in the inductor's magnetic field.
 
The magnetic field now generates a current in the opposite direction and thus charges the capacitor again, but with reversed polarity. Losses that occur are compensated by supplying energy. In this way, the oscillation is maintained. A part of the magnetic field is also radiated. The loop "sends".
 
Now to the starting question:
The difference is caused by the design of the capacitors.
 
The VVC is a two-electrode unit. The resonant voltage of the oscillating circuit is always present at the electrodes, alternating between positive and negative. The drive axle is electrically connected to one of the capacitor plates. So there is the full high voltage during operation. The electrical zero point of the loop is the mechanical middle of the loop.

 
The Butterfly-C consists of two capacitors connected in series. The inner plates are like a third electrode in the middle of the capacitor. The drive axle is connected to this. The voltage at this point is almost zero, as result of the addition of the outer voltages. The outer electrodes oscillate in terms of voltage around this midpoint. This is why you can attach the axle here without insulation. However, some differences in the two capacitors (synchronism) can also cause small voltages (a few volts) to occur. An isolation of the axle is recommanded but not essential.
 
 
73, Immo


ED MONTAIGNE
 

I am sure that your comments on mag loop capacitors are accurate, however when running 100 watts into the loop with approximately 5000 volts (very big gap between rotor and stator) across the butterfly. After about 2 minutes of transmitting, my directly connected 2 rpm 12vdc tuner drive motor quit(read smoked). Since I had several motors for other projects,  I  promptly changed them out and added an insulated  connector between the butterfly  variable capacitor shaft and the drive motor. That motor is still tuning the variable capacitor to this day.
Just thought I would share my experience with those who might be interested.

Thanks for all comments on the subject.


On Fri, Sep 9, 2022, 4:59 PM Allen Hill via groups.io <Allenanalog1=yahoo.com@groups.io> wrote:

Hi Immo, I think you have explained the issues perfectly.

I think it's important that users are aware of the mechanical makeup of capacitors used in Transmitting Loops. I've seen a number of loops built with plate capacitors that are not of the butterfly style. Depending on the mechanical methods used in the capacitor a large potential can be present on the shaft (during TX).

Thanks for helping to add clarity to this issue!

73
Allen Hill
KI4QCK



On September 9, 2022, at 12:52 PM, "Immo, DL5KB" <dl5kb@...> wrote:


Hi all,
 
Why does the axle of a VVC needs to be isolated and that of a Butterfly-C not?
 
I think it would be going too far to describe the electrical states during operation using mathematical formulas at this point. I'll try to do that with a few drawings and a more simple explanation.
 
If tuned, a mag-loop is a parallel resonant circuit. Let's start with the capacitor. The states on the capacitor change from charged positive to zero and then to charged negative. These states alternate in the form of a sine wave in time with the resonant frequency.
 
The charge on the capacitor generates a current in the parallel inductance (loop) until the capacitor is completely discharged. When the capacitor is discharged, all of the energy is stored in the inductor's magnetic field.
 
The magnetic field now generates a current in the opposite direction and thus charges the capacitor again, but with reversed polarity. Losses that occur are compensated by supplying energy. In this way, the oscillation is maintained. A part of the magnetic field is also radiated. The loop "sends".
 
Now to the starting question:
The difference is caused by the design of the capacitors.
 
The VVC is a two-electrode unit. The resonant voltage of the oscillating circuit is always present at the electrodes, alternating between positive and negative. The drive axle is electrically connected to one of the capacitor plates. So there is the full high voltage during operation. The electrical zero point of the loop is the mechanical middle of the loop.

 
The Butterfly-C consists of two capacitors connected in series. The inner plates are like a third electrode in the middle of the capacitor. The drive axle is connected to this. The voltage at this point is almost zero, as result of the addition of the outer voltages. The outer electrodes oscillate in terms of voltage around this midpoint. This is why you can attach the axle here without insulation. However, some differences in the two capacitors (synchronism) can also cause small voltages (a few volts) to occur. An isolation of the axle is recommanded but not essential.
 
 
73, Immo


Immo, DL5KB
 

hi Ed,

thanks for sharing your experience, and, fine that you were able to solve the issue. 

Perhaps another thought about possible issues touching butterfly-C. Therein are found the differences between theory and practice :-)
Some (more) voltage at the driving shaft (middle of the C) may occur, if
- the loop is grounded, but not right to the electrical middle of the loop...
   (The parts of bonding the cap to the loop prolongs the loop physically. If these connections are of different length at both sides,
    this will shift the electrical ground-(neutral)point of the loop respective. Think about: Grounding ever happens if using a gamma match to drive the loop!)
- the two halves of the butterfly are not of equal capitance.
  (If plates are of different aligned distances at both sides or plates are not of equal size. Just if homebrew, this may occur often.)

73, Immo


Robbert J. van Herksen
 

Here is a interesting video from Jerri Elsworth / AI6TK
Where she is visualising high voltage-distribution on magloops using neon tubes.

IMHO a great way to see where the voltages are where we don’t want them.

73 de Robbert TA2/PA3BKL
The dutch guy living (it up) in Istanbul


 XS Max (512Gb)

On 10 Sep 2022, at 10:21, Immo, DL5KB <dl5kb@...> wrote:

hi Ed,

thanks for sharing your experience, and, fine that you were able to solve the issue. 

Perhaps another thought about possible issues touching butterfly-C. Therein are found the differences between theory and practice :-)
Some (more) voltage at the driving shaft (middle of the C) may occur, if
- the loop is grounded, but not right to the electrical middle of the loop...
   (The parts of bonding the cap to the loop prolongs the loop physically. If these connections are of different length at both sides,
    this will shift the electrical ground-(neutral)point of the loop respective. Think about: Grounding ever happens if using a gamma match to drive the loop!)
- the two halves of the butterfly are not of equal capitance.
  (If plates are of different aligned distances at both sides or plates are not of equal size. Just if homebrew, this may occur often.)

73, Immo

--
73 de Robbert / TA2IX (aka PA3BKL)
The dutch guy living in Istanbul


Robbert J. van Herksen
 

Oops, silly me.

I forget the link:


Sorry guys! 

73 de Robbert / PA3BKL

 XS Max (512Gb)

On 10 Sep 2022, at 18:34, Robbert J. van Herksen via groups.io <rescueteam@...> wrote:

Here is a interesting video from Jerri Elsworth / AI6TK
Where she is visualising high voltage-distribution on magloops using neon tubes.

IMHO a great way to see where the voltages are where we don’t want them.

73 de Robbert TA2/PA3BKL
The dutch guy living (it up) in Istanbul


 XS Max (512Gb)

On 10 Sep 2022, at 10:21, Immo, DL5KB <dl5kb@...> wrote:

hi Ed,

thanks for sharing your experience, and, fine that you were able to solve the issue. 

Perhaps another thought about possible issues touching butterfly-C. Therein are found the differences between theory and practice :-)
Some (more) voltage at the driving shaft (middle of the C) may occur, if
- the loop is grounded, but not right to the electrical middle of the loop...
   (The parts of bonding the cap to the loop prolongs the loop physically. If these connections are of different length at both sides,
    this will shift the electrical ground-(neutral)point of the loop respective. Think about: Grounding ever happens if using a gamma match to drive the loop!)
- the two halves of the butterfly are not of equal capitance.
  (If plates are of different aligned distances at both sides or plates are not of equal size. Just if homebrew, this may occur often.)

73, Immo

--
73 de Robbert / TA2IX (aka PA3BKL)
The dutch guy living in Istanbul

--
73 de Robbert / TA2IX (aka PA3BKL)
The dutch guy living in Istanbul