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MeasurementBlues
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CB story
MeasurementBlues   8/6/2014 6:02:04 PM
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As promised, here's my CB radio story. CB radio broadcast on 27MHz. Commercial TV analog ch 2 was 54-60 MHz the second harmonic. The third harmonic, 81 MHz, was analog ch 5. CB interfered but it was far worse on ch 2. In NYC where I started, ch 2 is CBS. Here in Boston, ch 2 is PBS. So it was a bigger deal in NYC. After we moved, we discovered that if you keyed your mic in your car CB while driving past a local furniture store, the store's alarm would sound.

David Ashton
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Re: CB story
David Ashton   8/6/2014 6:22:02 PM
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Martin: I take it you meant to say: "The third harmonic, 81 MHz" ??

perl_geek
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Historical corrections
perl_geek   8/6/2014 6:39:11 PM
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HMS Sheffield was hit by an Exocet missile fired by an aircraft, https://www.youtube.com/watch?v=IUZu8bvxJs4  not a torpedo from a ship. The article is correct that it was the motor that set fire to the superstructure. (That wasn't the only time an Exocet failed to explode on impact. http://www.nytimes.com/1984/06/26/world/iraqi-exocet-hit-tanker-but-failed.html  )

The Forrestal incident  was caused by a power surge in the aircraft that wasn't related to the ship's radar. http://secondsfromdisaster.net/s03e08-aircraft-carrier-explosion-uss-forrestal-fire/ 

MeasurementBlues
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Re: CB story
MeasurementBlues   8/6/2014 11:38:07 PM
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Thanks for the correction of 81 MHz. I typed the post on my phone.

MeasurementBlues
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Re: Historical corrections
MeasurementBlues   8/6/2014 11:39:41 PM
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Thanks for the historical corrections. If you watch the video, you'll see that Ott mentioned the EMC Directive as being implemented in 1986. It was actually 1996. His slides were correct.

MeasurementBlues
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Re: Historical corrections
MeasurementBlues   8/6/2014 11:41:12 PM
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"The Forrestal incident  was caused by a power surge in the aircraft"

Ahh but what caused the power surge? Even so, it's still an EMC issue.

perl_geek
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Re: Historical corrections
perl_geek   8/7/2014 9:52:04 AM
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"Ahh but what caused the power surge?". The switch from external to internal power.  See http://www.warbirdsnews.com/warbird-articles/important-planes-navy-carriers-fly.html

Normally, the switch-over didn't cause a problem, because of an isolation switch on the rocket pod, secured by a pin. IIRC, the "Remove Before Flight" tag had  been fluttering in high winds, and pulled the pin loose. As often happens, one safety mechanism thwarted another.

I wouldn't classify it as an EMC incident; it was more an electrical power management issue. (And a reminder not to point loaded weapons at anything you don't want to destroy.)

 



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