The usefulness of the square-wave response plots (as you and I have
conducted) relies primarily on the complexity of the received waveform and
system bandwidth. Even in the case of a CW square-wave-like signal, a
gently sloping rise/decay time (e.g., raised-cosine CW waveform), greatly
reduces occupied transmitted bandwidth and the square-wave impulse response
of the transformer becomes less meaningful.
OTOH, if there was to exist some form of data mode in which short rise/fall
times are required, then a wider, flatter, overall receive bandwidth is
required. Presently, I know of no such common data modes for amateur use,
but this may apply to some commercial and/or military data modulation
methods.
Regardless of whether this is an issue or non-issue for amateur use, I have
demonstrated (on the Elecraft mail list through Yahoo) that the problem is
cleanly solved in even the cheapest datacom transformers through a simple
termination of the secondary winding. The peace of mind of knowing that a
sound card will not be over-driven by a brief spike in transformer overshoot
is certainly worth cost of a single resistor between the transformer and
sound card input.
Paul, W9AC
----- Original Message -----
From: "Jack Smith" <[EMAIL PROTECTED]>
To: "Paul Christensen" <[EMAIL PROTECTED]>
Cc: "'Elecraft'" <[email protected]>
Sent: Saturday, September 20, 2008 6:42 PM
Subject: Re: [Elecraft] K3 related - non-linear audio transformer behavior
Paul:
I've revised my non-linear transformer page in two respects:
1. Added the plot you requested. (Almost at the bottom of the page)
2. Added square wave ringing data for four transformers, although I am not
at all convinced that square wave ringing is an appropriate figure of
merit for a transformer used in a narrowly bandwidth limited
communications receiver.
The page is:
http://www.cliftonlaboratories.com/non-linear_transformer_behavior.htm
Paul Christensen wrote:
Jack:
With regard to the plots under "Comparisons and Conclusions," and also
under "Frequency Response Compared," is it possible to change the source
Z from 600-ohms to 50-ohms and re-test?
It would be an interesting exercise to see if THD (at ~ 1V RMS) and the
high-end frequency response of the Bourns transformer changes
significantly. Tnx!
Paul, W9AC
----- Original Message ----- From: "Jack Smith"
<[EMAIL PROTECTED]>
To: "'Elecraft'" <[email protected]>
Sent: Saturday, September 20, 2008 8:02 AM
Subject: [Elecraft] K3 related - non-linear audio transformer behavior
I've spent the last two weeks measuring and analyzing non-linear
behavior of several audio transformers, focusing on the Tamura TTC-108
used as isolation transformers in the K3.
My data and analysis is now available at
http://www.cliftonlaboratories.com/non-linear_transformer_behavior.htm
Jack K8ZOA
www.cliftonlaboratories.com
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