Indeed, similar harmonic and IMD distortion are created inside the LINE
IN transformer. The question is their level and importance.
The LINE IN transformer, however, is fed by a 10:1 voltage divider, 604R
in series with 62R shunted across the transformer primary. This
arrangement provides a lower drive impedance to the transformer, around
56 ohms as a matter of fact. (Assumes the LINE IN port is driven by a
low impedance source, which I believe is the case for the typical sound
card output.) 56 Ohms is low enough to see significant THD improvement
over a straight 604 ohm series resistor according to my measurements.
It should be possible to measure harmonics generated by the input
transformer, perhaps using the monitor function. I'm too far behind on
other projects to work on it at the moment, however.
Jack
Paul Fletcher wrote:
Jack,
Thanks for the research - very interesting and it looks like a simple fix to
improve the performance of the K3 significantly. You've got me wondering now
though about DATA-A modes. As the K3 uses the same transformer for line in
your work suggests that the transmit performance will be affected by the
sound card output impedance - worth considering at least.
Cheers,
Paul M1PAF
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
