Creating a high ratio transformer...

[Lamont Cranston]

Newsreader problem since updating Thunderbird, so GG until I get thay solved.

In a thread about a low impedance transformer for a Q meter, it was suggested two cascaded two 10 to 1 transformers be
used to get 100 to 1 ratio. 3C90 material was used.
I have 3F3 that is similar but a little lower ui. I\'m hoping flat 100kHz to 100MHz, but really only need 30MHz.

I have pot cores, are there any, tricks to winding that will make for better coupling or less strays?


Is there any advantage to a wide band for the one turn secondary vs a single 22 gauge wire? I have copper strap
or brass shim stock.

Put the one turn on outside, on inside?

I have room for 12 turns, put the one turn right in the middle, 5 turns on each side?

I\'ve built one, but I need a better jig to measure with the NanoVna. Parts on the way.

Thanks, For you input, Mikek

 

[Anthony William Sloman]

On Monday, October 17, 2022 at 12:08:36 AM UTC+11, Lamont Cranston wrote:

Newsreader problem since updating Thunderbird, so GG until I get that solved.

In a thread about a low impedance transformer for a Q meter, it was suggested two cascaded two 10 to 1 transformers be
used to get 100 to 1 ratio. 3C90 material was used.

https://elnamagnetics.com/wp-content/uploads/library/Ferroxcube-Materials/3C90_Material_Specification.pdf

It\'s a manganese -zinc ferrite so not good at anything over a1 MHz.

> I have 3F3 that is similar but a little lower ui. I\'m hoping flat 100kHz to 100MHz, but really only need 30MHz.

http://www.stades.co.uk/Ferrites/3f3.pdf

Still a manganese-zinc ferrite, and not much better.

Nickel-zinc ferrites go higher, and might get you to 30MHz.

> I have pot cores, are there any, tricks to winding that will make for better coupling or less strays?

Toroids or c-cores might be better for high frequency work. The parallel capacitance along each winding can be a problem at high frequencies, and inter-winding capacitance can be worse.

<snip>

--
Bill Sloman, Sydney

 

[whit3rd]

On Sunday, October 16, 2022 at 6:08:36 AM UTC-7, Lamont Cranston wrote:

Newsreader problem since updating Thunderbird, so GG until I get thay solved.

In a thread about a low impedance transformer for a Q meter, it was suggested two cascaded two 10 to 1 transformers be
used to get 100 to 1 ratio. 3C90 material was used.
I have 3F3 that is similar but a little lower ui. I\'m hoping flat 100kHz to 100MHz, but really only need 30MHz.

I have pot cores, are there any, tricks to winding that will make for better coupling or less strays?

Pot cores are excellent for coupling, but for strays you need to apply some tape. Mylar
tape between layers lowers capacitance (but adjacent winding-to-winding has such low relative voltage
that capacitive energy there is minor). Cloth tape and varnish was the old-school approach.
For the wire coming out of the center you want to preapply spaghetti tubing (to space it off from
the outer layers).

I\'d consider using foil for the one-turn, and put it in the center of the pot core (I assume you\'re using
a one-section spool?) so that it is an easy-to-wind core for the many-turns layers. If you
want to put a static shield over it, you want (of course) to make a second foil for that.

Is there any advantage to a wide band for the one turn secondary vs a single 22 gauge wire? I have copper strap
or brass shim stock.

Current in a sheet is a better match to most transformer flux coupling models than that from a single round ring.

Put the one turn on outside, on inside?

The one-fat-turn on inside minimizes resistance of t he low-Z winding by limiting length. The
higher-Z outer winding is less power loss because less current there.
Going with foil the inner winding takes very little of the throat.

 

[Lamont Cranston]

On Monday, October 17, 2022 at 3:45:08 AM UTC-5, whit3rd wrote:

On Sunday, October 16, 2022 at 6:08:36 AM UTC-7, Lamont Cranston wrote:
Newsreader problem since updating Thunderbird, so GG until I get thay solved.

In a thread about a low impedance transformer for a Q meter, it was suggested two cascaded two 10 to 1 transformers be
used to get 100 to 1 ratio. 3C90 material was used.
I have 3F3 that is similar but a little lower ui. I\'m hoping flat 100kHz to 100MHz, but really only need 30MHz.

I have pot cores, are there any, tricks to winding that will make for better coupling or less strays?
Pot cores are excellent for coupling, but for strays you need to apply some tape. Mylar
tape between layers lowers capacitance (but adjacent winding-to-winding has such low relative voltage
that capacitive energy there is minor). Cloth tape and varnish was the old-school approach.

In a previous job, we used 3M foam tape to add spacing between windings. Also used mylar tape.

For the wire coming out of the center you want to preapply spaghetti tubing (to space it off from
the outer layers).

I generally just cover possible shorting areas with the mylar tape, but I do have shrink tube that would work.

I\'d consider using foil for the one-turn, and put it in the center of the pot core (I assume you\'re using
a one-section spool?) so that it is an easy-to-wind core for the many-turns layers.

Yes, one section bobbin. Maybe I don\'t understand, it is easiest to wind the 10 turns first, add a spacing layer, then put the 1 turn
sheet winding on, other wise it is difficult the get the leads out for a sheet winding on the inside. Or so it seems.


> If you want to put a static shield over it, you want (of course) to make a second foil for that.

I have done that shield on a Flag Antenna (directional MF antenna) to prevent unwanted signal ingress, but, I put the shield between the to layers,
What is the advantage of a shield in this situation?
Also with battery operation, do I connect it to an external ground or low side of the LC connection? (Q meter, series tuned)
One time build, so I\'ll put in the effort to add shields if effective.

Is there any advantage to a wide band for the one turn secondary vs a single 22 gauge wire? I have copper strap
or brass shim stock.

Current in a sheet is a better match to most transformer flux coupling models than that from a single round ring.

Put the one turn on outside, on inside?
The one-fat-turn on inside minimizes resistance of t he low-Z winding by limiting length. The
higher-Z outer winding is less power loss because less current there.
Going with foil the inner winding takes very little of the throat.

I\'ll see if I can work out the lead exiting problem with the sheet winding going on first to reduce losses.
Thanks for the input, Mikek

 

[Lamont Cranston]

I\'ll see if I can work out the lead exiting problem with the sheet winding going on first to reduce losses.
Thanks for the input,
Mikek

OK, I have the inner foil turn figured our drawn glued to 0.004\" brass shim stock, cut out and wrapped on the bobbin.
Now, I need to know about the shield, Is it needed? Outside? Between layers?
And if needed what is is it\'s purpose?
Thanks, Mikek
https://www.dropbox.com/s/lxqe64u3wjbg2px/Q%20meter%203F3%20ONE%20TURN%20OUTLINE.jpg?dl=0

 

[Anthony William Sloman]

On Tuesday, October 18, 2022 at 6:09:56 AM UTC+11, Lamont Cranston wrote:

I\'ll see if I can work out the lead exiting problem with the sheet winding going on first to reduce losses.
Thanks for the input,
Mikek
OK, I have the inner foil turn figured our drawn glued to 0.004\" brass shim stock, cut out and wrapped on the bobbin.
Now, I need to know about the shield, Is it needed? Outside? Between layers?
And if needed what is is it\'s purpose?

https://www.dropbox.com/s/lxqe64u3wjbg2px/Q%20meter%203F3%20ONE%20TURN%20OUTLINE.jpg?dl=0

https://www.amazon.com/Grounding-Shielding-Techniques-Instrumentation-3rd/dp/0471838055

Ralph Morrison is very informative about coping with capacitance in transformers. His book was the first place I ran into the idea of double screening, where the first screen caught the incoming electric charge and had a voltage drop across it as the current was bled away to ground, and the second screen shielded the sensitive bits from the voltage excursions across the first screen.

--
Bill Sloman, Sydney

 

[Lamont Cranston]

On Monday, October 17, 2022 at 7:16:12 PM UTC-5, bill....@ieee.org wrote:

On Tuesday, October 18, 2022 at 6:09:56 AM UTC+11, Lamont Cranston wrote:
I\'ll see if I can work out the lead exiting problem with the sheet winding going on first to reduce losses.
Thanks for the input,
Mikek
OK, I have the inner foil turn figured our drawn glued to 0.004\" brass shim stock, cut out and wrapped on the bobbin.
Now, I need to know about the shield, Is it needed? Outside? Between layers?
And if needed what is is it\'s purpose?

https://www.dropbox.com/s/lxqe64u3wjbg2px/Q%20meter%203F3%20ONE%20TURN%20OUTLINE.jpg?dl=0

https://www.amazon.com/Grounding-Shielding-Techniques-Instrumentation-3rd/dp/0471838055

Ralph Morrison is very informative about coping with capacitance in transformers. His book was the first place I ran into the idea of double screening, where the first screen caught the incoming electric charge and had a voltage drop across it as the current was bled away to ground, and the second screen shielded the sensitive bits from the voltage excursions across the first screen.

--
Bill Sloman, Sydney

I ordered it. I tried to get an inter-library loan, but the library is understaffed and they aren\'t doing inter-library loans at this time. Grumble!
Mikek