[Elecraft] K3, diversity and noise reduction

[Harry Yingst via Elecraft]

It would be interesting to see if that feature could be added.



-------- Original message --------
From: Don Wilhelm <w3fpr at embarqmail.com> 
Date: 05/26/2015  8:26 PM  (GMT-05:00) 
To: Tony McRae <ajm at ttecs.com.au>, elecraft at mailman.qth.net 
Subject: Re: [Elecraft] K3, diversity and noise reduction 

Tony,

You are looking at information about how to compensate two unequal 
receivers for true diversity reception - two orthogonally opposed 
antennas receiving the same signal.
The K3 makes that easy with a sub-receiver that is identical with the 
main receiver and they are phase locked together in diversity. When 
placed in diversity mode (using two antennas hopefully having different 
polarity or directional characteristics), you will hear enhancement of 
the reception from whichever antenna is receiving the best signal - you 
have each receiver in each of your ears, and the human brain will 
respond to the best signal.  No phase adjustment is necessary.

OTOH, if you are looking to reduce the noise of your plasma TV and 
routers, that is another form of reception that could (but not 
necessarily) be related to diversity.  You would want to use a 
directional antenna aimed at the noise source to feed one receiver while 
being able to adjust the amplitude and phase of that noise signal to 
cancel out the noise source.
It is possible that you could use the K3 with subRX to do that, the AF 
and RF gain controls will do the amplitude part of the process and if 
you provide an external mechanism for changing the phase of the two 
antennas, you may be successful.  The easiest phase change is simply to 
flip the noise receive antenna terminals which should achieve a 180 
degree phase shift, but the actual phase shift will depend on several 
other factors such as the length of the antenna feedlines and the 
physical placement of the antennas (which control the arrival time of 
the noise signal at the antennas).

So, yes, it is possible that with suitable antennas placed properly, the 
K3 with subRX *could* serve as a noise cancelling system, but it was not 
designed for that purpose, it was designed to counter propagation 
effects such as fading due to polarization.

73,
Don W3FPR

On 5/25/2015 9:00 PM, Tony McRae wrote:
> I have been watching some youtube clips showing how by adjusting the phase and amplitude of two received signals on a diversity receiver local noise can be reduced by more than 20db.
> This would be particularly useful to me as I have the dirtiest plasma TV on one side of me and a gaggle of cheap ADSL routers on the other. When pointed at them with my yagi the noise floor on 20-15m is over S7.
>
> The equipment used in the clip was the ANAN 100D SDR.
> Is anyone aware if this technique is possible using the K3 dual receivers?
> I have not found any place in the manual where it is possible to alter the phase of the secondary or primary signals.
>
> Thanks for reading this
>
> Tony VK4CH
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