Update HeterodyneFrequency for PyQLab compatibility.
Update HeterodyneFrequency for PyQLab compatibility.

--BRJ

Plourde-Research-Lab/Qlab,BBN-Q/Qlab,rmcgurrin/Qlab,rmcgurrin/Qlab,BBN-Q/Qlab,rmcgurrin/Qlab,Plourde-Research-Lab/Qlab,BBN-Q/Qlab,Plourde-Research-Lab/Qlab,rmcgurrin/Qlab,BBN-Q/Qlab