Basic concentric design

[golfnut]

I know this topic is hung, drawn and quartered... But I have never made one and want to get a confirm or otherwise..

Is it like this pic..?

Its the direction of turns, and placement ie buck inside Rx etc??



S

[Aziz]

Hi golfnut,

the winding orientation is correct. To minimize the number of turns count for the bucking coil, RX and bucking coil should have same size (maximal inductive coil coupling).
If bucking coil is smaller than RX, you would need more turns for the bucking coil.

Aziz

[Tinkerer]

The way you have the leads, they pick up quite a bit of residual signal. This can be used to help fine-tune the balance.

Once you have the balance set, the remaining lead length should be twisted to reduce the residual.

To calculate the coupling between the TX and RX coils you take the surface area or flux area of the TX and divide by the flux area of the RX. The coupling gives you the relation between TX and BU coils.

[Carl-NC]

You can place the bucking coil just outside the RX, just inside, just above, or just below. It doesn't make a lot of difference.

[SWL]

RX direction has be SUCH....

[dfbowers]

RX direction has be SUCH....
[ATTACH]24032[/ATTACH]

One consideration is that the grounded end of the Tx coil should be the end off of the bucking coil. The grounded end of the Rx coil should be Rx finish, closest to the bucking coil. This may be required for best null but may be determined by the project in question.

Here is a quote from one of George Payne's articles:
"About the connection of the Receive in relation to the Feedback wind. It’s seems to be a very minor thing and not important. The only reason this is a problem is due to the closeness (touching) of the windings. If they were an inch or two apart it would not be a problem. There is one other little point that I forgot to mention. Again this is very important. The Feedback winding must be connected to the un-driven side of the Transmit tank circuit. For the same reasons I mentioned before this reduces the capacitive coupling between the Transmit and Receive which will allow the resultant Receive null to be small."

[golfnut]

Thx for the info all.

The minor confusion I still have is ..

winding direction.

Question is is Aziz and me correct or Don, George and SWL.

I know Don has made a few of these puppies and Ive seen them run on U tube - So Ill go with Don et al


For the avoidance of doubt - Tx and Rx are wound in the same direction - buck the other way. Location of buck no big deal..

Steve

[Davor]

If you really don't have to, don't commit the shield to any of the coil wires. You can always commit it to whatever you need in a connector.

[dfbowers]

If you really don't have to, don't commit the shield to any of the coil wires. You can always commit it to whatever you need in a connector.

Yes, thank you Davor.. I thought about that after I posted. The grounding would be project specific.

[golfnut]

If I bought this 9" spider coil cover - has anyone got a foolproff recipe for it?


Or an approx design this 10 by 8 XP cover. I use 0.2mm Rx and 0.3mm Tx usually.



I estimate some of the tesoro Rx coils on their 9x8 spider to have about 400t ??

S

[Carl-NC]

Thx for the info all.

The minor confusion I still have is ..

winding direction.

Question is is Aziz and me correct or Don, George and SWL.

I know Don has made a few of these puppies and Ive seen them run on U tube - So Ill go with Don et al


For the avoidance of doubt - Tx and Rx are wound in the same direction - buck the other way. Location of buck no big deal..

Steve

The bucking coil is always connected so that current flows in the opposite direction from the TX coil. Bucking coils are often wound as a separate coil, not a continuation of the TX winding, so that the winding direction doesn't matter but how you hook it up does. Remember, for any coil one lead is the beginning of the clockwise direction and the other lead is the beginning of the counter-clockwise direction.

RX coil direction really doesn't matter except that the RX signal may be inverted, which also may not matter. If it does, simply reverse the RX connections.

[kt315]

[golfnut]

Great I think thats all pretty clear now. Ill get a coil cover and have a play.


In a commercial coil, the shell is carbonised inside or a paint or somesuch, graphited paper insert etc etc.

One thing that remains a puzzle for me is this.. The coil is now e-field screened from above - when in use over the ground ?

Sorry to be the muppet that asks all of the questions

S

[joop]

The graphite stuff is present both at the top and bottom of the coil form. The screen at the top helps against electrical interference (high-voltage wires, cell phones, etc.).

[Pete B1]

Here's a photo of a tesoro coil i opened. Hope it helps.