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Modulation transformer question




 
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KB5MD
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« on: May 11, 2020, 01:57:05 AM »

What design characteristics determine the frequency response limitations of a modulation transformer?
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w4bfs
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« Reply #1 on: May 11, 2020, 10:58:00 AM »

there are 2 major influences on transformer frequency response:  winding inductance and leakage reactance

the best way to get full understanding is to look at modeling characteristics - first and second order at least for audio concerns

the winding inductance is the major factor in low frequency response.  the inductive reactance (Xl = 2pifL) sets the essential impedance of the winding at any specific frequency.  this is of course with any other windings disconnected.

ex:    a transformer has a winding inductance of 10 Henrys.   what is its impedance value at 20 Hz ?   Xl.= 2(3.14)(20){10) =1256 Ohms
 
this says this parallel impedance would be barely acceptable for use at 1200 ohms load at 20 Hz min.

if you study the transformer models and attendant equations you will see that thesis not a trivial matter  Wink

the leakage reactance is an unwanted (generally) facet of transformer construction and limits high frequency response.  careful attention to construction helps to limit this to what appears to be a small series choke inside the xfmr.  this is generally not specified but can be experimentally determined.
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« Reply #2 on: May 12, 2020, 09:19:48 AM »

What design characteristics determine the frequency response limitations of a modulation transformer?

Pages 4 and 7 of this document shows the low and high frequency models of a transformer:

https://www.jensen-transformers.com/wp-content/uploads/2014/08/Audio-Transformers-Chapter.pdf


Phil - AC0OB
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