Diversity Receive as Noise Cancelling

[K7TV]

AB7E wrote:

 

>a.  Elecraft to make the phase lock between the two receivers remain
constant as the frequency is changed.  >Ideally the phase differential of
the local oscillators would be zero ... either forced that way by the DSP or
>by using the same L.O. for both receivers.  If that wasn't possible, it
would still be usable if the >differential were known or could be
interrogated by a command.

>

>b.  Someone to write a simple bit of software for the computer that took
the sound card inputs, shifted and >processed them, and then feed them back
out through the sound card to headphones or speakers.

 

As far as I remember from the K3 block diagram, each receiver has its own
DSP that feeds one AF channel, and each DSP has no knowledge of what goes on
in the other DSP. If this is a correct understanding, then the K3 DSP would
need operator input to change amplitude and phase in order to cancel noise.
Doing the job in a computer sound card and CPU would have a distinct
advantage in that adjustment of phase and amplitude could be automatic.

 

73,

Erik K7TV

 

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[Guy, K2AV]

The problem with "automatic" is that it needs to know what out of the
composite signal you are getting do you want nullified.  You will
still need manual input for this.  Further, this is in effect only on
the frequency you are on.  Only RF cancellation has the broadband
nullification.

73, Guy.

On Tue, Nov 30, 2010 at 2:26 PM, Erik Basilier <[hidden email]> wrote:

> AB7E wrote:
>
>
>
>>a.  Elecraft to make the phase lock between the two receivers remain
> constant as the frequency is changed.  >Ideally the phase differential of
> the local oscillators would be zero ... either forced that way by the DSP or
>>by using the same L.O. for both receivers.  If that wasn't possible, it
> would still be usable if the >differential were known or could be
> interrogated by a command.
>
>>
>
>>b.  Someone to write a simple bit of software for the computer that took
> the sound card inputs, shifted and >processed them, and then feed them back
> out through the sound card to headphones or speakers.
>
>
>
> As far as I remember from the K3 block diagram, each receiver has its own
> DSP that feeds one AF channel, and each DSP has no knowledge of what goes on
> in the other DSP. If this is a correct understanding, then the K3 DSP would
> need operator input to change amplitude and phase in order to cancel noise.
> Doing the job in a computer sound card and CPU would have a distinct
> advantage in that adjustment of phase and amplitude could be automatic.
>
>
>
> 73,
>
> Erik K7TV
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[Bill W4ZV]

Guy, K2AV wrote

The problem with "automatic" is that it needs to know what out of the
composite signal you are getting do you want nullified.  You will
still need manual input for this.  Further, this is in effect only on
the frequency you are on.  Only RF cancellation has the broadband
nullification.

I agree.  Using a phasing unit you're combining the desired (i.e. from RX antenna) and undesired (i.e. from noise sense antenna) signals to minimize the combined antenna pattern's rejection of the undesired signal (azimuth and elevation).  This allows one to place a null on a localized area of thunderstorm activity (i.e. not just a single coherent signal) by manually adjusting for best overall noise rejection.  Of course it also works well to null someone, not in the desired direction, that may be causing QRM (i.e. to the sides or rear), assuming you have a good sense antenna in that direction.  It will NOT work well for either noise or QRM generally inline with the desired RX direction.

73,  Bill