I should get the web page detailing the cardioid loop finished tomorrow evening UK time.
I'll confirm if a short counterpoise works tomorrow.
The improvement in signal to noise ratio over a conventional loop is very noticeable. Instead of having the two sharp nulls of a conventional loop there is a wide angle to the rear of the antenna pattern where noise or interfering signals are attenuated.
There is no noticeable pick up from nearby electrical equipment that I can measure.