[RTTY] RadioShack transformer IMD

[Don Hill AA5AU]

I bought a RadioShack "Ground Loop Isolator" today and decided to test the IMD of the transformers (there are two in the device).

I used Digipan in its IMD measurement mode and looped the output of my soundcard directly back into the input with a
straight-through cable. Playing with the output and input levels, the typical IMD measurement in Digipan was about -61 to -58. I
then inserted one of the transformers of the RadioShack device and the IMD did not change. I played with the levels and was able to
put the transformer into saturation and could see the signal in the display, but with every level tested, and regardless of
frequency (used 1kHz, 2kHz & 3kHz) when the level was below saturation there was no difference whether or not the transformer was in
line.

I was expecting a higher IMD reading with the transformer inserted between the input and output of the soundcard as compared to the
straight-through cable. What am I missing?

73, Don AA5AU
http://www.aa5au.com
http://www.rttycontesting.com