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

[Phil Alexander]

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





-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.394 / Virus Database: 268.8.3/358 - Release Date: 6/7/06