Diversity Receive as Noise Canceling? (was K3 Plasma TV and other non OT junque)

[Dick Dickinson]

Hi Ed,

That's a good question.  I've wondered that myself.  Perhaps some more
knowledgeable will chime in.


73,
Dick - KA5KKT

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Along this line of discussion, I wonder if those who have the KRX3
could use it as a noise cancelling receiver (similar to the
anc-4)?  If the aux receiver output in diversity mode could be
reverse phased to cancel noise using a "noise sniffer" antenna. I
realise that would eliminate use of the aux Rx for other uses but in
the face of extreme noise interference would that matter?


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[Don Wilhelm-4]

  Dick,

Most of the noise cancelling systems reverse the phase of one of the
antennas and feed the combined result to the receiver,  If the noise
antenna receives only noise, the noise will disappear and only the
signal will be present, but in practice, the noise antenna picks up some
signal too, and will attenuate the signal to the extent of the signal
pickup on the noise antenna.

In theory, it should work equally well at the output of two receivers
each being fed from separate antennas.
Of course, with two full receivers involved, the complexity of
adjustments to achieve the same amplitude on each receiver becomes more
of a challenge, and the phasing adjustment requirements for the noise
antenna are still present.

For those interested in trying it, I would suggest that you "use the
brain" to do the final filtering and simply swap the speaker or
headphone connections of one channel to observe the results.  If you
remember phasing of stereo speakers, then you will understand how just
reversing the speaker (or headphone) leads will result in cancellation
or re-enforcement of sound.

So what I am saying is that it should be relatively easy to try - let us
know the results.

73,
Don W3FPR

On 11/27/2010 6:00 PM, Edward Dickinson, III wrote:
> Hi Ed,
>
> That's a good question.  I've wondered that myself.  Perhaps some more
> knowledgeable will chime in.
>
>
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[K7TV]

I am not familiar with the ANC-4, but I assume it is similar to the MFJ
noise cancellers. Those units are not "receivers" but work with the weak
antenna signals at the originally transmitted frequencies. Aside from some
signal buffering, such a unit essentially provides the capability to
continuously adjust the phase difference and relative gain between the two
inputs, and to do this at a wide variety of ham band frequencies. If you
instead feed the two antennas into twin receivers, you would have to adjust
amplitude and phase at the output. At audio frequency it is hard enough to
build a phase shifting network that maintains constant phase shift over a
reasonable audio frequency range, but if you want to make that phase shift
continuously knob adjustable it becomes really hard. The DSP in the K3 has
potential as a precision phase shifter, but consider that the
frequency-dependent phase shifts that may be caused by the different xtal
filter specimens and analog components in each receiver may have already
messed up the phase relationships by the time the signal gets to DSP or
receiver output.

 

73,

Erik K7TV

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