[BC] Null Distortion (WAS: Westinghouse at NAB)

[miltron]

In some instances, can't there be overmodulation in or near the nulls due to having more power in the sidebands than carrier power?

-----Original Message-----
>From: Phil Alexander <dynotherm at earthlink.net>
>Sent: Jun 8, 2006 1:18 PM
>To: Broadcasters' Mailing List <broadcast at radiolists.net>
>Subject: Re: [BC] Null Distortion (WAS: Westinghouse at NAB)
>
>On 2 Jun 2006 at 19:29, WFIFeng at aol.com wrote:
>
>> If you drive along I-95 through Stratford, CT, right near Exit 31, you will 
>> hear WFIF's null. It's pretty deep, but fairly small. At 55Mph, you're in and 
>> out of it in about 2 seconds. It sounds more like the selective fading effect 
>> you get from a SW station than SSB.
>
>What happens with some DA's is a phase reversal zone and the reversal
>azimuth is slightly skewed in the sidebands. This will be in an area
>where one side of the null is + carrier and the other side is - carrier.
>The result is you hear HF audio 180 deg our of phase with LF audio
>in a very narrow azimuth range. It is also possible to get the same
>effect from reradiation off power lines, cell towers etc. There is a
>good side. This zone is easy to hear when searching for the center of
>a null while doing an array tune up.
>
>---------------------------------------------
>Phil Alexander, CSRE, AMD
>Broadcast Engineering Services and Technology 
>(a Div. of Advanced Parts Corporation) 
>Ph. (317) 335-2065   FAX (317) 335-9037
>
>
>
>