[CQ-Contest] End to background noise

[Morel Grunberg]

Few months ago I heard that "Analog Devices" has a new 
integrated circuit ( SSM-2166 ) who is able to cancel the
background noise present in an audio signal coming from
a microphone. 

After I received the 15-pages data specs & application note
I discovered that this tiny 14-pin IC can solve my background
problems coming from the amplifier blower, computer fan, TV
and radio sound, children cries and a busy street down under 
my window shack.

After I've built the circuit and  began the tests, I was astonished
by the effectiveness of the IC: simply all the background noise
was attenuated with an average of 35dB down of my voice. The 
air reports were excellent and all my partners asked me what
I'm using to cancel the noises, after a short demonstration with
the unit bypass switch on/off. Now, I can use my processor at
compression levels much bigger than the previous 3-4 dB I used
before due to the high background noise with extremely low 
distortions ( typical 0.1-0.2% ). Absolute no voice alterations or
any kind of time delays, echo or signal rise/fall timing related
problems
(as in other products) were found.   

The unit is quite simple: an IC, 5-6 capacitors, 3-4 resistors and
5 small variable resistors. The supply is 5Vdc at 15mA or 12-25V
if a simple 7805 regulator is used. The board can be as small as
3x4cm and should be placed in a small shielded box.

Some modifications should be made on the original schematic diagram
and setting procedure given in the "Analog Devices" application note.

The unit was tested with Yaesu/Kenwood/Icom transceivers and 
performed very well with no RF feedbacks. The only difference is
of course, the microphone connector wiring.

Few of my local friends built also this small unit with very good
results 
too. As I've heard, a complete kit and and an assembled kit will be
available very soon in U.S. Also, an article on this issue will appear
in "QST" very soon, as I've heard from some U.S. friends. 

The unit is very useful for SSB contest teams when few operators
are crying in their microphones at same time creating a stressing
noisy environment.
 
The "Analog Devices" complete documentation can be found on their
home page ( www.analog.com ) and can be read with Acrobat Reader
software. If you don't have this program on your computer, you can
download for free immediately via a link to "Adobat".
 
The 15-pages can be received also from Customer Support Hot Line
automatic fax : 1-800-262-5643.
 
73 de Morel, 4X1AD
 



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