The present invention provides an OFDM symbol generating apparatus. The developing device further includes electromagnets for forming a magnetic field inside the toner supply pipe to create a magnetic brush shutter by means of the electromagnets. The audio equipment may also include a handle attached to the first protective bar, a second protective bar flexibly connected to the housing, andor a connector assembly flexibly connecting the first protective bar to the housing. Thus, a smaller, less powerful and less costly coherent radiation source can be utilized. The oxidizer solution forms an oxidized layer on remaining contaminants. Another welding system is provided that includes an engine, a compressor coupled to the engine and a monitor circuit configured to monitor the duration of operation of the compressor by monitoring engagement of the clutch.