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Re: 50 ohms to 0.02 ohm transformer

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"amdx" <nojunk@knology.net> wrote in message 
news:nvfrar$295$1@dont-email.me...
> On 11/3/2016 11:56 AM, Tim Wescott wrote:
>> On Thu, 03 Nov 2016 09:57:09 -0500, amdx wrote:
>>
>>> On 11/3/2016 8:58 AM, Jeroen Belleman wrote:
>>>> On 2016-11-03 13:55, 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
>>>>
>>>> A bandwidth ratio of only three should be dead-easy,
>>>> but the 20 mOhm impedance may spell trouble.
>>>> The single-turn winding should be fat and compact.
>>>> A single nH of stray inductance (!) or ten mOhms of resistance would
>>>> ruin performance. I think I would implement it as several single-turn
>>>> windings in parallel, distributed around a toroid. What will you
>>>> connect to the 20mOhm side?
>>>
>>>   A 20mOhm resistor.
>>>    I'm replacing a tube osc, I'm not able to follow the coax back to the
>>> tube output on the schematic, so I don't even have a start to figure out
>>> the tube output impedance. I'm starting to think it is not low.
>>>   But it is able to drive 1 amp through the 0.02 ohm resistor to develop
>>> 20mv.
>>>
>>>
>>>
>>>> Why would you need low A_l? The usual rule of having the reactance of
>>>> one winding four times the terminal impedance is only a minimum. There
>>>> is no harm in going higher. There would be if you did it by using more
>>>> turns though.
>>>>
>>>>
>>> My calculations tell me that with an AsubL of 75 it take 29 turns.
>>> This still doesn't get my a 50 to 1 turn ratio.
>>> If I use a core with an AsubL of 2340, I only need 5 turns, with that I
>>> can't get a 50 to 1 turns ratio.
>>>
>>>> Use a toroid. Gapped cores are for energy storage,
>>>> not for transformers.
>>>>
>>>> Jeroen Belleman
>>>
>>>   I'll restate my problem,
>>> I want to substitute a more stable signal generator for the internal
>>> signal generator in my Boonton 260A Q meter. The osc. in the 260A drives
>>> a 0.02 ohm resistor. It actually does this through a piece of coax,
>>> so I doubt it really has a 0.02 ohm output impedance. Could be I'm
>>> chasing a spec. I don't need to.
>>>   One advantage I have is I only want 4mv of drive across the 0.02 ohm
>>> resistor, also I can adjust the signal generator output to set the
>>> voltage regardless of transformer/connection losses.
>>>    Thanks for the multiple single turn winding in parallel idea.
>>>                              Still open to suggestions,
>>>                                           Thanks, Mikek
>>>
>>> PS.
>>> Next project is an RF detector to measure the 4mv signal, I want a
>>> circuit to drive my multimeter. I suspect I'll need a preamp before the
>>> detector to get any linearity. I do have a scope I can use to get a
>>> useful calibration.
>>
>> Your calculations show you that you need a _minimum_ of 29 turns, not
>> _exactly_ 29 turns.  29 is less than 50, so if you feel bound and
>> determined to maintain that ratio, use 50 turns and be happy.
>
>  Yes, I stated that in my first post.
>
>>
>> What's probably a better way (and what's probably being done in the
>> meter) is to not bother matching to that resistor, but rather to build an
>> amplifier that can work into a low impedance (or whatever the impedance
>> is when transformed by that coax and whatever is ahead of it),
>
> I don't know, the schematic on the Last page of this pdf. It looks to me 
> like the osc tube drives the 0.02 ohms directly.
>  http://www.hparchive.com/Boonton/Boonton-Manual-260A.pdf
>
>>and just
> accept whatever inefficiencies result.
>
>> If all you want is for the thing to generally operate the way it does now
>> but with a more stable oscillator, you may be best served by either
>> turning the current oscillator into an amplifier stage to be driven by
>> your oscillator, or injection-locking it.
>>
>
>  That's beyond my capability, I have an HP 8640B that has a frequency 
> lock.
>  Boonton produced an accessory to sub in another signal generator, it was 
> designed so you could lower the frequency of operation. It was a 500 ohm 
> to 0.03 ohm coupling transformer.
>> http://www.angelfire.com/electronic/funwithtubes/images/100_2598-B.jpg
>
>> http://www.angelfire.com/electronic/funwithtubes/images/100_2597-B.jpg
>
>                     Thanks for your help, Mikek
>
>

The coax is driven from the winding connected to pins 1 &2 of the turret. 
That winding couples RF from the plate winding connected to pins 4 & 8. The 
coax feeds the series load of the thermocouple and the 0.02 ohm resistor.

Regards,
Tom 

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50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 07:55 -0500
  Re: 50 ohms to 0.02 ohm transformer Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-11-03 15:12 +0200
    Re: 50 ohms to 0.02 ohm transformer John Larkin <jjlarkin@highlandtechnology.com> - 2016-11-03 10:55 -0700
      Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 16:56 -0500
        Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 20:36 -0500
        Re: 50 ohms to 0.02 ohm transformer Syd Rumpo <usenet@nononono.co.uk> - 2016-11-08 23:35 +0000
        Re: 50 ohms to 0.02 ohm transformer Lasse Langwadt Christensen <langwadt@fonz.dk> - 2016-11-08 15:51 -0800
          Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-08 21:45 -0600
          Re: 50 ohms to 0.02 ohm transformer Jasen Betts <jasen@xnet.co.nz> - 2016-11-10 03:28 +0000
      Re: 50 ohms to 0.02 ohm transformer Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-11-04 10:41 +0200
        Re: 50 ohms to 0.02 ohm transformer Jeroen Belleman <jeroen@nospam.please> - 2016-11-04 10:54 +0100
      Re: 50 ohms to 0.02 ohm transformer bill.sloman@ieee.org - 2016-11-04 06:00 -0700
        Re: 50 ohms to 0.02 ohm transformer Jeroen Belleman <jeroen@nospam.please> - 2016-11-04 14:10 +0100
          Re: 50 ohms to 0.02 ohm transformer John Larkin <jjlarkin@highlandtechnology.com> - 2016-11-04 08:08 -0700
      Re: 50 ohms to 0.02 ohm transformer "Tim Williams" <tiwill@seventransistorlabs.com> - 2016-11-04 22:13 -0500
  Re: 50 ohms to 0.02 ohm transformer Jeroen Belleman <jeroen@nospam.please> - 2016-11-03 14:58 +0100
    Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 09:57 -0500
      Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 09:59 -0500
      Re: 50 ohms to 0.02 ohm transformer Tim Wescott <seemywebsite@myfooter.really> - 2016-11-03 11:56 -0500
        Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 12:15 -0500
          Re: 50 ohms to 0.02 ohm transformer Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-11-03 19:37 +0200
            Re: 50 ohms to 0.02 ohm transformer makolber@yahoo.com - 2016-11-03 10:49 -0700
            Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 13:19 -0500
            Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 13:31 -0500
              Re: 50 ohms to 0.02 ohm transformer Tim Wescott <seemywebsite@myfooter.really> - 2016-11-03 14:38 -0500
            Re: 50 ohms to 0.02 ohm transformer Tim Wescott <seemywebsite@myfooter.really> - 2016-11-03 14:39 -0500
              Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-03 16:52 -0500
                Re: 50 ohms to 0.02 ohm transformer whit3rd <whit3rd@gmail.com> - 2016-11-03 18:00 -0700
              Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-04 06:26 -0500
                Re: 50 ohms to 0.02 ohm transformer Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-11-04 15:20 +0200
                Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-04 09:33 -0500
                Re: 50 ohms to 0.02 ohm transformer Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-11-04 21:21 +0200
          Re: 50 ohms to 0.02 ohm transformer "tom" <tmiller11147@verizon.net> - 2016-11-03 14:02 -0400
  Re: 50 ohms to 0.02 ohm transformer Winfield Hill <hill@rowland.harvard.edu> - 2016-11-03 10:25 -0700
  Re: 50 ohms to 0.02 ohm transformer Jeff Liebermann <jeffl@cruzio.com> - 2016-11-04 11:24 -0700
    Re: 50 ohms to 0.02 ohm transformer Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-11-04 21:24 +0200
      Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-04 16:46 -0500
        Re: 50 ohms to 0.02 ohm transformer amdx <nojunk@knology.net> - 2016-11-05 12:37 -0500
  Re: 50 ohms to 0.02 ohm transformer mike <ham789@netzero.net> - 2016-11-05 02:29 -0700

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