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 <[email protected]>
Date: 05/26/2015 8:26 PM (GMT-05:00)
To: Tony McRae <[email protected]>, [email protected]
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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