Forums

50 ohms to 0.02 ohm transformer

Started by amdx November 3, 2016
On 4.11.16 20:24, Jeff Liebermann wrote:
> On Thu, 3 Nov 2016 07:55:14 -0500, amdx <nojunk@knology.net> wrote: > >> I want to build a 50 ohm to 0.02 ohm transformer. >> It needs a 50 to 1 turns ratio. >> It takes a low A sub L core to make such a thing. >> I have a toroid with an A sub L of 75. That only needs >> 29 turns for my frequency of interest 500KHz to 1700kHz. >> I also have some potcores that I could gap to lower the A sub L. >> What would make a better transformer a toroid or a gapped potcore? >> I plan 50 turns with a 1 turn secondary. >> What problems can I expect with a 1 turn secondary? >> Thanks, Mikek > > > Are you perhaps building an AM broadcast band to power line coupler? > If so, how much RF power? If not, just ignore the following. > > Way back on college daze, I helped build such a contrivance for the > campus AM radio station. The problem was how to keep 60Hz AC from > going back through the transformer and AM modulating the final stages. > The fix was to use a ferrite toroid, which coupled the RF quite > nicely, but none of the 60Hz. As I barely recall from 46 years ago, > it was an ordinary ferrite toroid core about 2" OD. However, I don't > recall the ferrite material used or number turns involved. No need > for a pot core since the transformer was inside an aluminum box. I'll > see if I can find some details (time permitting). Google for "carrier > current AM transmitter" > > Also, do you really need broadband for your unspecified application? > Going from 0.5MHz to 1.7MHz without tuning is nice, but if your > transmitter doesn't change frequency, an LC tuned arrangement (tapped > coil or two capacitors) might be easier than a toroid.
It seems that the OP is hacking an old Boonton Q meter, attempting to extend its measurement range, without the proper theoretical background to do it properly. Measuring higher Q's does not need (or tolerate) increased excitation to the DUT. -- -TV
On 11/4/2016 2:24 PM, Tauno Voipio wrote:
> On 4.11.16 20:24, Jeff Liebermann wrote: >> On Thu, 3 Nov 2016 07:55:14 -0500, amdx <nojunk@knology.net> wrote: >> >>> I want to build a 50 ohm to 0.02 ohm transformer. >>> It needs a 50 to 1 turns ratio. >>> It takes a low A sub L core to make such a thing. >>> I have a toroid with an A sub L of 75. That only needs >>> 29 turns for my frequency of interest 500KHz to 1700kHz. >>> I also have some potcores that I could gap to lower the A sub L. >>> What would make a better transformer a toroid or a gapped potcore? >>> I plan 50 turns with a 1 turn secondary. >>> What problems can I expect with a 1 turn secondary? >>> Thanks, Mikek >> >> >> Are you perhaps building an AM broadcast band to power line coupler? >> If so, how much RF power? If not, just ignore the following. >> >> Way back on college daze, I helped build such a contrivance for the >> campus AM radio station. The problem was how to keep 60Hz AC from >> going back through the transformer and AM modulating the final stages. >> The fix was to use a ferrite toroid, which coupled the RF quite >> nicely, but none of the 60Hz. As I barely recall from 46 years ago, >> it was an ordinary ferrite toroid core about 2" OD. However, I don't >> recall the ferrite material used or number turns involved. No need >> for a pot core since the transformer was inside an aluminum box. I'll >> see if I can find some details (time permitting). Google for "carrier >> current AM transmitter" >> >> Also, do you really need broadband for your unspecified application? >> Going from 0.5MHz to 1.7MHz without tuning is nice, but if your >> transmitter doesn't change frequency, an LC tuned arrangement (tapped >> coil or two capacitors) might be easier than a toroid. > > > It seems that the OP is hacking an old Boonton Q meter, attempting > to extend its measurement range, without the proper theoretical > background to do it properly.
Pretty true, I'm a fish monger by trade.. The transformer was an attempt to use a different more stable osc. Abandoning that for now, in favor of getting my Q measurements done.
> Measuring higher Q's does not need > (or tolerate) increased excitation to the DUT.
You're correct again, in "does not need increased excitation" but I'm not increasing excitation, I'm lowering it. I'm lowering the drive voltage from 20mv to 4 mv this changes the multiplier of the Q meter from 1 to 5. With that I can measure up to a Q of 1250. If you would like to be helpful, I'd like to measure the low mv RF signal. I could use a design for a diode detector to measure down to 3.33mv with the output driving a DMM. I would like a low capacitance input, probably a fet input MPF102/2N3819 which I have, and an amp using 2N2222, 2N2907, 2n3904, or 2n3906 which I have. I also have 2n4401/4403. 1n34A will be the diode I'd have. Frequency range 500kHz to 1700kHz. I want it to run from 9V. FWIW, the source impedance is 0.02 ohms. I understand it will be non linear, that is fine, I can build up a cheat sheet of the 4 voltage setting I have interest in, 3.33mv, 4mv, 5mv and 6.66mv. I can use my scope to get enough accuracy to make the cheat sheet. Thanks, Mikek
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message 
news:4aum1c1gog519isp42g1hhcac03beg96ki@4ax.com...
> Leakage inductance can matter. >
Out of 0.02 ohms, that's a guarantee! Out of 50 ohms, a pretty good match should be reasonable, up to whatever the electrical length of the primary winding is (at which point it looks like a transmission line over the secondary "ground plane").
> It would be interesting to make a toroidal transformer where the > 1-turn winding wraps around the entire core. Visualize that! It can be > approximated by paralleling multiple 1t windings.
Easy enough. This is a cross section. Imagine it's revolved around the axis on the right (so the gray core part is a torus, and everything else is a disk, cylinder or hole shape). http://seventransistorlabs.com/Images/OPT_XSection.png Oh, the copper colored vertical sides connect to a plate shorting across the top, of course. I'd show a picture of the finished thing, but it's pretty boring, like looking at a bank vault from the "concrete walls" side. :^) Or if you want an inline structure (like a coaxial current transformer), you start with a pipe, slit it, then put a larger pipe on over the slit (with discs to short it to the first pipe, on either side of the slit). The core and windings go inside the space thus created. In particle accelerators, the bunches are so small (sub-ns) that they can't afford any windings at all; transmission lines are simply connected in parallel across the gap! Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
On 11/3/2016 5:55 AM, amdx wrote:
> I want to build a 50 ohm to 0.02 ohm transformer. > It needs a 50 to 1 turns ratio. > It takes a low A sub L core to make such a thing. > I have a toroid with an A sub L of 75. That only needs > 29 turns for my frequency of interest 500KHz to 1700kHz. > I also have some potcores that I could gap to lower the A sub L. > > What would make a better transformer a toroid or a gapped potcore? > > I plan 50 turns with a 1 turn secondary. > > What problems can I expect with a 1 turn secondary? > > Thanks, Mikek
The guys who make CD Spot Welders should know about this stuff.
On 11/4/2016 4:46 PM, amdx wrote:
> On 11/4/2016 2:24 PM, Tauno Voipio wrote: >> On 4.11.16 20:24, Jeff Liebermann wrote: >>> On Thu, 3 Nov 2016 07:55:14 -0500, amdx <nojunk@knology.net> wrote: >>> >>>> I want to build a 50 ohm to 0.02 ohm transformer. >>>> It needs a 50 to 1 turns ratio. >>>> It takes a low A sub L core to make such a thing. >>>> I have a toroid with an A sub L of 75. That only needs >>>> 29 turns for my frequency of interest 500KHz to 1700kHz. >>>> I also have some potcores that I could gap to lower the A sub L. >>>> What would make a better transformer a toroid or a gapped potcore? >>>> I plan 50 turns with a 1 turn secondary. >>>> What problems can I expect with a 1 turn secondary? >>>> Thanks, Mikek >>> >>> >>> Are you perhaps building an AM broadcast band to power line coupler? >>> If so, how much RF power? If not, just ignore the following. >>> >>> Way back on college daze, I helped build such a contrivance for the >>> campus AM radio station. The problem was how to keep 60Hz AC from >>> going back through the transformer and AM modulating the final stages. >>> The fix was to use a ferrite toroid, which coupled the RF quite >>> nicely, but none of the 60Hz. As I barely recall from 46 years ago, >>> it was an ordinary ferrite toroid core about 2" OD. However, I don't >>> recall the ferrite material used or number turns involved. No need >>> for a pot core since the transformer was inside an aluminum box. I'll >>> see if I can find some details (time permitting). Google for "carrier >>> current AM transmitter" >>> >>> Also, do you really need broadband for your unspecified application? >>> Going from 0.5MHz to 1.7MHz without tuning is nice, but if your >>> transmitter doesn't change frequency, an LC tuned arrangement (tapped >>> coil or two capacitors) might be easier than a toroid. >> >> >> It seems that the OP is hacking an old Boonton Q meter, attempting >> to extend its measurement range, without the proper theoretical >> background to do it properly. > > Pretty true, I'm a fish monger by trade.. > The transformer was an attempt to use a different more stable osc. > Abandoning that for now, in favor of getting my Q measurements done. > >> Measuring higher Q's does not need >> (or tolerate) increased excitation to the DUT. > > You're correct again, in "does not need increased excitation" > > but I'm not increasing excitation, I'm lowering it. > > I'm lowering the drive voltage from 20mv to 4 mv this changes > the multiplier of the Q meter from 1 to 5. With that I can measure > up to a Q of 1250. > > If you would like to be helpful, I'd like to measure the low mv RF > signal. I could use a design for a diode detector to measure down to > 3.33mv with the output driving a DMM. I would like a low capacitance > input, probably a fet input MPF102/2N3819 which I have, and an amp using > 2N2222, 2N2907, 2n3904, or 2n3906 which I have. I also have 2n4401/4403. > 1n34A will be the diode I'd have. Frequency range 500kHz to 1700kHz. I > want it to run from 9V. FWIW, the source impedance is 0.02 ohms. > I understand it will be non linear, that is fine, I can build up a > cheat sheet of the 4 voltage setting I have interest in, 3.33mv, 4mv, > 5mv and 6.66mv. I can use my scope to get enough accuracy to make the > cheat sheet. > > Thanks, Mikek > > >
I have pretty well solved what was a ground loop problem putting the 60Hz signal on my osc. So the transformer is not so important now. Maybe later, because I would still like a more stable osc. Solving the ground loop allows me to use a scope or RF meter to monitor injection voltage, but the scope allows turning drive to zero, the RF meter still only goes to 2mv. Mikek
On 03/11/2016 21:56, amdx wrote:

<snip>

> > Hows this John, > >> https://www.dropbox.com/s/6klg2v2awamchb5/2001-12-31%2023.00.00-122.jpg?dl=0 >> > >> https://www.dropbox.com/s/3gmnukf4u7kawx3/2001-12-31%2023.00.00-120.jpg?dl=0 >> > > I haven't tested it yet. > > Mikek
I can't see the first one, but that second picture makes me want one. All I need now is a reason... Cheers -- Syd
Den torsdag den 3. november 2016 kl. 22.56.41 UTC+1 skrev amdx:
> On 11/3/2016 12:55 PM, John Larkin wrote: > > On Thu, 3 Nov 2016 15:12:53 +0200, Tauno Voipio > > <tauno.voipio@notused.fi.invalid> wrote: > > > >> On 3.11.16 14:55, amdx wrote: > >>> I want to build a 50 ohm to 0.02 ohm transformer. > >>> It needs a 50 to 1 turns ratio. > >>> It takes a low A sub L core to make such a thing. > >>> I have a toroid with an A sub L of 75. That only needs > >>> 29 turns for my frequency of interest 500KHz to 1700kHz. > >>> I also have some potcores that I could gap to lower the A sub L. > >>> > >>> What would make a better transformer a toroid or a gapped potcore? > >>> > >>> I plan 50 turns with a 1 turn secondary. > >>> > >>> What problems can I expect with a 1 turn secondary? > >>> > >>> Thanks, Mikek > >> > >> For a toroid, a turn is simple: A wire through the toroid > >> hole is a turn, a wire outside is nothing. > >> > >> IMHO, your real problem is on the 20 milliohm side to make > >> the circuit connections so that you're not going to lose all > >> of your signal in the connection resistances and inductances. > >> This is regardless which way you build your transformer. > > > > Leakage inductance can matter. > > > > It would be interesting to make a toroidal transformer where the > > 1-turn winding wraps around the entire core. Visualize that! It can be > > approximated by paralleling multiple 1t windings. > > > > http://www.spaceneedle.com/wp-content/uploads/2013/08/view-from-heli-250x211.jpg > > > > > > > Hows this John, > > > https://www.dropbox.com/s/6klg2v2awamchb5/2001-12-31%2023.00.00-122.jpg?dl=0 > > > https://www.dropbox.com/s/3gmnukf4u7kawx3/2001-12-31%2023.00.00-120.jpg?dl=0 > > I haven't tested it yet. > > Mikek
I wonder if it would be an advantage to split the ring opposite the wire connection so it isn't a closed closed loop
On 11/8/2016 5:51 PM, Lasse Langwadt Christensen wrote:
> Den torsdag den 3. november 2016 kl. 22.56.41 UTC+1 skrev amdx: >> On 11/3/2016 12:55 PM, John Larkin wrote: >>> On Thu, 3 Nov 2016 15:12:53 +0200, Tauno Voipio >>> <tauno.voipio@notused.fi.invalid> wrote: >>> >>>> On 3.11.16 14:55, amdx wrote: >>>>> I want to build a 50 ohm to 0.02 ohm transformer. >>>>> It needs a 50 to 1 turns ratio. >>>>> It takes a low A sub L core to make such a thing. >>>>> I have a toroid with an A sub L of 75. That only needs >>>>> 29 turns for my frequency of interest 500KHz to 1700kHz. >>>>> I also have some potcores that I could gap to lower the A sub L. >>>>> >>>>> What would make a better transformer a toroid or a gapped potcore? >>>>> >>>>> I plan 50 turns with a 1 turn secondary. >>>>> >>>>> What problems can I expect with a 1 turn secondary? >>>>> >>>>> Thanks, Mikek >>>> >>>> For a toroid, a turn is simple: A wire through the toroid >>>> hole is a turn, a wire outside is nothing. >>>> >>>> IMHO, your real problem is on the 20 milliohm side to make >>>> the circuit connections so that you're not going to lose all >>>> of your signal in the connection resistances and inductances. >>>> This is regardless which way you build your transformer. >>> >>> Leakage inductance can matter. >>> >>> It would be interesting to make a toroidal transformer where the >>> 1-turn winding wraps around the entire core. Visualize that! It can be >>> approximated by paralleling multiple 1t windings. >>> >>> http://www.spaceneedle.com/wp-content/uploads/2013/08/view-from-heli-250x211.jpg >>> >>> >> >> >> Hows this John, >> >>> https://www.dropbox.com/s/6klg2v2awamchb5/2001-12-31%2023.00.00-122.jpg?dl=0 >> >>> https://www.dropbox.com/s/3gmnukf4u7kawx3/2001-12-31%2023.00.00-120.jpg?dl=0 >> >> I haven't tested it yet. >> >> Mikek > > I wonder if it would be an advantage to split the ring opposite the > wire connection so it isn't a closed closed loop >
I wondered that also. btw, the wires you see are for the 50 turn primary connection. For the one turn secondary, the connections can be anywhere around the circumference to the two buss bars. (16gauge wire) Mikek