Here is another version and setup of using an EMF COIL underneath an iphone's MIC...
to send CW to the iphone mumble input using the iphone mic's EMF PICKup from a ferrite bobbin core inductor...
the frequency of the VLF CW keyer sender to the coil is @8Khz... and on the laptop's mumble receiver,
a VLF CW bandpass filter is used to only allow the 8Khz CW to get through and that removes all of the
audio over air pickup by the IPHONE mic , a tv, people in the other room, fan noise clocks, birds outside .. etc...
only the 8Khz VLF CW gets through(instead of listening to cw at 8Khz, it is regenerated to 777hz by two simple apps
ZAMGATE and a sine wave generator...)