It is unlawful for any person, firm, co partnership, association or corporation to operate or cause to be operated, any machine, device, apparatus or instrument of any kind whatsoever within the corporate limits of the city between the hours of five p.m. and twelve midnight, the operation of which causes electrical interference with radio reception – provided, however, that in case of imperative emergency X ray pictures or examinations may be made if the machine or apparatus used therefor is properly equipped to avoid all unnecessary or reasonably preventable electrical interference with radio reception.