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K3, diversity and noise reduction

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Tony McRae

K3, diversity and noise reduction

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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David Woolley (E.L)

Re: K3, diversity and noise reduction

This is normally done ahead of the aerial input and will work with any
receiver that supports such an input.

Effectively what you are doing is creating a null in the antenna pattern
in the direction of the source.

It needs an effective point source to work well. If the signal is
getting out through the mains lead, it may be more difficult.

http://www.g8jnj.net/rfnoisecancellation.htm
http://www.eham.net/reviews/detail/1138
http://www.eham.net/reviews/detail/1205

Incidentally, the first article claims a 30dB, rather than 20dB null.
--
David Woolley
Owner K2 06123

On 26/05/15 02:00, 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.

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Don Wilhelm-4

Re: K3, diversity and noise reduction

In reply to this post by Tony McRae

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:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Elecraft mailing list

Re: K3, diversity and noise reduction

In reply to this post by Tony McRae

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

-------- Original message --------
From: Don Wilhelm <[hidden email]>
Date: 05/26/2015 8:26 PM (GMT-05:00)
To: Tony McRae <[hidden email]>, [hidden email]
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:

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dmb@lightstream.net

Re: K3, diversity and noise reduction

In reply to this post by Tony McRae

Tony,

I strongly recommend the DX Engineering NCC-1 for noise cancellation:
< http://www.dxengineering.com/parts/dxe-ncc-1 >

It is very effective at nulling out offending noise sources -- BUT, it
will do so for only one source at a time. You may find that nulling out
one of your sources will frequently be enough, depending upon the
direction of your yagi at the time.

I've had one for about three years, and wouldn't want to be without it.

73, Dale
WA8SRA

>
> 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

David Gilbert

Re: K3, diversity and noise reduction

In reply to this post by Elecraft mailing list

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 <[hidden email]>
> Date: 05/26/2015 8:26 PM (GMT-05:00)
> To: Tony McRae <[hidden email]>, [hidden email]
> 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:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

vk2rq

Re: K3, diversity and noise reduction

That's a good idea, Dave. The best place to do it would probably be
inside the DSP on the K3 itself, but failing that, you could do it in
your PC, and the advantage is you could give a better visual
indication of what is going on that what could be achieved on the K3's
LCD display.

73, Matt VK2RQ

On Wed, May 27, 2015 at 2:01 PM, David Gilbert <[hidden email]> 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 <[hidden email]>
>> Date: 05/26/2015 8:26 PM (GMT-05:00)
>> To: Tony McRae <[hidden email]>, [hidden email]
>> 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:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]
>>>
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

NK7Z

Re: K3, diversity and noise reduction

In reply to this post by David Gilbert

No kidding, I was thinking of suggesting this as well...
--
Thanks and 73's,
For equipment, and software setups and reviews see:
www.nk7z.net

For MixW support see;
http://groups.yahoo.com/neo/groups/mixw/info
For Dopplergram information see:
http://groups.yahoo.com/neo/groups/dopplergram/info
For MM-SSTV see:
http://groups.yahoo.com/neo/groups/MM-SSTV/info

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 <[hidden email]>
> > Date: 05/26/2015 8:26 PM (GMT-05:00)
> > To: Tony McRae <[hidden email]>, [hidden email]
> > 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:[hidden email]
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >> Message delivered to [hidden email]
> >>
> > ______________________________________________________________
> > 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
> > Message delivered to [hidden email]
> > ______________________________________________________________
> > 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
> > Message delivered to [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
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Alan Bloom

Re: K3, diversity and noise reduction

In reply to this post by vk2rq

The suggestion is to use the two identical receivers in the K3 to null
noise and interference. The idea is to connect each receiver to a
different antenna so the signals arrive with different phases. The
phase difference will generally be different for the desired signal and
the interference or noise, so by combining the two signals with the
proper amplitude and phase you can null out the undesired signal.

There are units you can buy today that do that by combining the RF
signals from the two antennas before they are sent to the receiver. The
question is whether you can do it at audio frequencies rather than at
RF. Theoretically you can, since the demodulated SSB signal is just a
frequency translation of the RF. If that works, it would be simply a
question of new firmware in the K3, since the audio from the two
identical receivers is already available to the DSP.

The issue is that the amplitude and phase responses of the crystal
filters in the two receivers are not identical. To get a good null, the
difference in the phase shift through the two filters would have to
track within much less than 360 degrees across the passband. In other
words, the variation of the difference in group delay would have to be
much less than 1/8 usec with an 8.215 MHz IF.

A 2.5 kHz bandwidth filter probably has on the order of a msec group
delay. I doubt the two filters typically track each other to better
than a few usec across the passband, if that.

You probably could get a good null at a single CW frequency, but I don't
see how you could hope to get the null to hold across the passband.

Alan N1AL
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