[Elecraft] K3, diversity and noise reduction

Wed May 27 00:01:30 EDT 2015

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
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to w3fpr at embarqmail.com
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to hlyingst at yahoo.com
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to xdavid at cis-broadband.com