Newsgroups: rec.aviation.student
Subject: Re: The level out and the flare
From: jbolinger@lintek.com (J L Bolinger)
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In article <19981002024831.08202.00001949@ngol06.aol.com>, rodfarlee@aol.com 
says...
>
>As you've pointed out, FM receivers have a 10.7 MHz intermediate
>frequency.  When tuned to the high end of the FM band, 97 to 108 MHz, 
>an FM receiver has potential to interfere with VOR and localizer reception.
>
>In the nav band, VORs are 108-118 MHz and localizers are 108-112 MHz.  
>The FM range that can interfere with them is 10.7 MHz lower,  97.3 to 
>107.3 MHz.  This is the upper half of the FM band only.
>
>Specifically, my home airport's ILS localizer is 110.3 MHz.  If I tune a 
>plastic Walkman-style FM to 110.3 - 10.7 = 99.6 MHz, my localizer 
>flags OFF.  If I turn up the NAV radio audio, I can hear all kinds of 
>interference when a "Walkman" is within 30 feet of the airplane.  
>Our VOR is 114.0 MHz.  Same thing happens if a "Walkman" is tuned 
>to 114.0 - 10.7 = 103.3 MHz. 
>

And what if the portable radio has a local oscillator on the high
side?  It (the oscillator) will then be between 98.7 and 118.7 MHz, 
right in the Nav range!

>This is NOT true of an automotive AM/FM/CD with a steel chassis to 
>shield it.  That's what I have in my airplane.  The FAA will routinely 
>approve 337 forms for permanent installations in any airplane.  They
>require that you test for interference, as above.  Our shop says they
>have installed and tested dozens, and never found any interference.
>

My point exactly.

>So if you have a portable FM in the plane, check it for interference.  
>If you find any:
>- don't tune the FM above 97 MHz if you're using navaids*,
>- turn off the FM in IMC, when you're really relying on navaids!
>

If there is _any_ interference I would say don't use it at all.

>Also check whether the FM interference disappears when the CD is 
>playing.  On Sony Walkman FM/CD, it does; on others, it might not.
>

Another point I was making.  Radios will probably be worse, but other
electronics could also be a problem.


>* We NPR fans never get far above the low end of the FM band 
>anyway!  <grin>
>- Rod Farlee


Jim

