Products > Test Equipment
DIY Transformer for use with Bode Plots.
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joeqsmith:
I have no problem with the DIY toss something together.  I'm just trying to make sure I understand what you are presenting.  I am surprised how well things appear to work at lower frequencies and thought I could attempt to repeat your tests with some other configurations. 
mawyatt:
Surprised as well!! Did not expect the low frequency, or flatness performance, quite nice for a couple $ CM Filter reconfigured :-+

The low frequency impedance to the transformer is low, however the input sampling is across the transformer primary so this compensates some for the transformer low frequency characteristics.

Also quite pleased with how well the Siglent DSO behaves  :)

Best,
joeqsmith:
I tried wrapping 30 turns bifilar on two tape cores I had.   The performance was very poor.     

Primary inductance was 109.4mH
Leakage inductance was 4.1uH
Coupling capacitance was 119.8pF
Resistance 4-wire was 0.589 ohms
I didn't check the leakage as the freq response was so poor.
0.2dB 225Hz - 2.51MHz
Phase over this range is 21 degrees

To get below 100Hz, I would need to hunt down some better cores or start adding turns....   Interesting problem. 
T3sl4co1l:
Why -0.2dB?  The cutoff is arbitrary, and easily calibrated out.

Tim
joeqsmith:

--- Quote from: T3sl4co1l on May 24, 2022, 04:02:19 am ---Why -0.2dB?  The cutoff is arbitrary, and easily calibrated out.

--- End quote ---

I wanted to provide metrics with numbers.  Why specifically -0.2, I followed the link the OP provided which then took me to other links. I assumed that the OP read all of this as well which is why they had shown their first screen shot at 0.2dB/div.    In the one reference they mention the 0.1dB, for example:   


--- Quote ---This model boasts 10Hz to 45MHz bandwidth (watch out, this is not even -3dB bandwidth, “real” 0.1dB flatness is 100Hz to ca. 1MHz only). Capacitance is a quite large 150pF. Price is a few 100€.
--- End quote ---

They provide some constraints for their design:


--- Quote --- but lets try to formulate some specs:

    100Hz to several 100kHz with a phase shift below 5 degrees.
    amplitude flatness of less than 0.2dB over this range
    not more than ca. 20 Ohms resistance at the injected side
--- End quote ---

I had asked the OP about calibration and assumed it was somehow normalized but it made no sense to me that the phase would be zero as it would have to match the thru standard.  Maybe the Siglent has a way to compensate for the delay.   I would have started by showing an open and maybe a couple of attenuators to  give people some confidence in their data but as they said,


--- Quote ---This effort was just a quick DIYer to "see" if these cores would work and get familiar with the Closed Loop capability using the SDS2104X Plus and especially to "see" if this capability could be applied to high loop gain circuits such as Op Amp based circuits.

--- End quote ---


--- Quote ---For a more thorough test one would use full scope BW, controlled setup, quality short cables, connectors & such as you would expect for proper RF measurements...which this thread wasn't intended for!!

--- End quote ---

Similar to the last post about the UnUn, it's nothing I have any use for and just thought I would play along to add to the discussion.   My interest stems from the first data the OP presents where the show 0.2dB at 10Hz.  I have no idea if that's a problem with the setup or if its real.  Seemed very impressive.   As I posted, my first attempt was around 252Hz.  Hardly in the ball park.   
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