Herald: Where have you gone Air America

Eli Polonsky elipolo@earthlink.net
Thu Sep 21 02:45:39 EDT 2006

-----Original Message-----
>From: "A. Joseph Ross" <Joe@attorneyross.com>
>Sent: Sep 20, 2006 5:26 PM
>To: boston-radio-interest@rolinin.bostonradio.org, 
>Eli Polonsky <elipolo@earthlink.net>
>Subject: Re: Herald: Where have you gone Air America
>On 20 Sep 2006 Eli Polonsky wrote:
>> That's likely because you're going by the WTTT 1150 and WAZN 1470
>> transmitter site at the Lexington/Belmont/Waltham line. The proximity
>> to the 1150 signal is desensitizing your radio to 1200, and the 1470
>> signal is doing it to 1430 when you're that close to those towers.
>I'm familiar with those towers.  I first became aware of them when 
>they were still WCOP.  I suppose it's possible they could be causing 
>the problem I have, but I'm not sure I quite understand the mechanism 
>for how a signal on a nearby channel affects my reception.

In addition to the intermodulation factor with also nearby WWZN that Dan
mentioned, the other possible reason would be in your radio. If you have
a modern digital car tuner, many of them have an automatic attenuation 
circuit that reduces sensitivity when it receives extremely strong signals,
such as when driving nearby transmitters. 

It's purpose is to help reduce symptoms of RF overload such as splatter 
and the receiving of images, harmonics and intermodulation. The circuits 
are usually designed to reduce the sensitivity of a certain portion of the 
dial surrounding the very strong nearby signal, which can cause weak 
reception of other frequencies nearby the strong one on the dial.

The circuit replaces the old "Local/DX" switches, which used to have to 
be switched manually as needed when driving into strong signal areas. 
Though the old manual switches were much more common on FM than 
AM tuners, many digital car tuners employ the automatic attenuation 
circuit on both AM and FM.


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