Among some suggestions and questions I sent Tony in an e-mail, I
promised Tony I'd do a two tone test on some of the small 73 mix
cores he used.
I measured RF current through a string of four beads (one turn)
shunting a 50 ohm system, and watched IMD as power was increased.
There was absolutely no change in IMD until I applied almost ten
watts across the 50 ohm load. That's over 22 volts RMS!
The RF current flowing through the bead-path had to exceed 100 mA
RMS before any measurable increase in IMD appeared. (Noise and IMD
floor is over 85 dB below one tone of a two tone test in the set up I
By the way, the RF current level that produced an increase in IMD
also caused the beads to become very warm!
I would conclude from this data it is very unlikely the IMD is from
core saturation. Most receiver front ends would almost certainly be a
problem (or actually suffer component damage) long before the
transformer generated IMD.
It's a sure bet the problem is elsewhere.....like at the receiver
front end, a preamplifier, or other that contain semi-conductors.
Perhaps the IMD is external to the antenna, and the antenna is just
picking the IMD up from an external mixer that is re-radiating the
73, Tom W8JI
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