1502 INTERNATIONAL AGREEMENTS OTHER THAN TREATIES [55 STAT. 9.- All diathermy machines designed for the same service can operate on the same frequency without impairing their usefulness, since their operation is not affected by radiation from other machines. Operation on a specific frequency with a very close frequency tolerance is practicable, with little added cost. It is understood that the present design of diathermy equipment has to a great extent gravitated to frequencies above approxi- mately 12 megacycles, hence it is recommended that the sub- scribing countries consider requiring all diathermy machines to use not more than two frequencies in harmonic relation above 12 megacycles which will not interfere with existing radio assignments. The harmonic relationship between the two frequencies provides a further guarantee against inter- ference to radio-communication. 10. - Standards of good engineering practice are believe to be prac- ticable at the present time and consideration of the adoption by the governments of such standards at the earliest practi- cable date is recommended. The standards should include the following subjects: a) Frequencies to be used. b) Automatic frequency control. c) Frequency stability. d) Type of emission. e) Maximum power output. f) Harmonic radiation to be effectively suppressed. g) Internal circuits to be effectively shielded. h) Radiation from power supply connection to be eliminated. 11. - Where diathermy apparatus does not comply with the stand- ards whichmay be adopted by the subscribing countries should consider the desirability of requiring such apparatus to be operated in a properly shielded room. 12.- Such apparatus as carrier call systems and certain types of induc- tion furnaces and similar apparatus using medium or low frequencies should be required to restrict the generation of harmonics and make the necessary test to determine that radiation of signal does not result beyond a prescribed level. 13.- The interested administrations will interchange all information concerning the solution of the problem created by the serious interference caused by diathermy apparatus to radio com- munications
�
