OT: Noise Reduction?

[Martin-85]

Hello elecrafters,
i am looking for a device to reduce/eliminate the noise of a 2m ssb-receiver.

What the circuit should do: Reduce (or eliminate) the noise of the rx
when no signal is present, like a squelch, but much faster.

It should be an analog device, not a dsp-device.
It should be external ( e.g. input from the receiverŽs headphone
jack).

Background: A friend of mine runs a transponder 144Mhz ssb -> 432Mhz
fm.
The fun with ssb input and fm output is that 2 or more persons
can have a conference like on the telephone. There is no
interference (whistles when 2 signals present) like on fm , because there is no carrier in ssb.

We would like to eliminate or reduce the noise in the pauses.
I heard that musicians use a so called ŽnoisegateŽ, but could not find
any circuit on the web.

Any ideas anyone?
Lyle Johnson?


--
Best regards,
 Martin
K2 #2706                          mailto:[hidden email]


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[Robert-223]

It's doubtful you will be able to do this without some digital
processing involved.
You need to sample the signal and then apply adaptive digital filtering
with the ability to decern between noise and voice signals.  What you're
asking is a very complicated thing to do.  Analogue will give you
filtering but will not be able to get rid of all the noise since noise
itself is a complex waveform.

If you want to try a noise gate, you may get some success.  Several used
Behringer gear found on ebay have noise gates for not alot of money.

To some extent, DSP can do what you're asking as long as the noise is
not really strong.  Then again, DSP will reduce the noise by the amount
of Noise Reduction capable within the unit.

I think what you're trying to do is build an adaptive squelch.  There
are people working on this very concept right now.

Regards,
Robert VE3RPF



Martin wrote:

>Hello elecrafters,
>i am looking for a device to reduce/eliminate the noise of a 2m ssb-receiver.
>
>What the circuit should do: Reduce (or eliminate) the noise of the rx
>when no signal is present, like a squelch, but much faster.
>
>It should be an analog device, not a dsp-device.
>It should be external ( e.g. input from the receiverŽs headphone
>jack).
>
>Background: A friend of mine runs a transponder 144Mhz ssb -> 432Mhz
>fm.
>The fun with ssb input and fm output is that 2 or more persons
>can have a conference like on the telephone. There is no
>interference (whistles when 2 signals present) like on fm , because there is no carrier in ssb.
>
>We would like to eliminate or reduce the noise in the pauses.
>I heard that musicians use a so called ŽnoisegateŽ, but could not find
>any circuit on the web.
>
>Any ideas anyone?
>Lyle Johnson?
>
>
>--
>Best regards,
> Martin
>K2 #2706                          mailto:[hidden email]
>
>
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft   
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com
>
>
>  
>

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