[Elecraft] K3, diversity and noise reduction

[David Cole]

No kidding, I was thinking of suggesting this as well...  
-- 
Thanks and 73's,
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On Tue, 2015-05-26 at 21:01 -0700, David Gilbert wrote:
> I have on three different occasions requested of Elecraft that such a 
> feature be added to the K3.  Two of those requests never received a 
> response, while the third got a "we'll see if anyone in engineering is 
> interested" reply (apparently nobody was).
> 
> Personally, I think this is a significantly missed opportunity to expand 
> the usefulness of diversity reception in the K3, especially now that the 
> new synths retain phase lock when changing frequency. If even only one 
> receiver in the K3 had the ability to time shift the audio signal, it 
> would work.  The K3 already has separate volume controls and already has 
> the ability to mix the two channels.  With two antennas separated 
> horizontally (i.e., two verticals a suitable distance apart), the phase 
> could be adjusted to boost a desired signal by roughly 3db or null an 
> undesired signal (noise or QRM) by 20 to 30 db or more (depending upon 
> how stable the signals were). Directional antennas are not needed at all.
> 
> I also think it would be interesting, and maybe useful, to use two 
> antennas separated vertically, such as a couple of dipoles or yagis on a 
> tower.  Adjusting the phase could potentially drop a severe notch on an 
> interfering signal IN THE SAME DIRECTION as a desired signal.
> 
> Phase is preserved in the down conversion to audio so all this could be 
> accomplished at the audio level.  I'm not saying that's the best place 
> to do it, but worst case I'm going to learn enough software code to do 
> it myself using the sound card of my computer since nobody else seems 
> interested.
> 
> 73,
> Dave   AB7E
> 
> 
> On 5/26/2015 5:45 PM, Harry Yingst via Elecraft wrote:
> > 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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