The most unusual 'anchor that's ever followed me home

Jeffrey Herman jeffreyh at HAWAII.EDU
Wed May 27 11:43:39 EDT 1998

This should be an interesting thread - I encourage everyone to

Yesterday, a Federal Signal Corp. "air-raid" siren somehow ended
up in my garage - all 400 pounds of it. Model SD-10, 10 hp 240
VAC single phase motor driving an aluminum rotor. The rotor has two rows
of opennings - 12 opennings in one row, 9 in the other, which produce
2 tones, in a freq'y ratio of 4-to-3 (for example, 400 and 300 Hz
tones). The stationary portion (the "stator") also has the same number
of opennings which align exactly with those of the rotor. The rapid
openning and closing of these matching ports is how the tones are

The spec plate says the motor shaft spins at 3300 rpm, or 55 rps.
Hence, at top speed, one hears 660 and 495 Hz tones (plus all
the harmonics generated - this is what gives these sirens their
distinctive sound).

The plate also says "F.L. Amps 54." (What is "F.L."?)

One question - how do I apply 3-phase 240vac to a single-phase

73 from Nevada,
Jeff KH2PZ/7

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