Thanks, Jim
There is a particular type of "diversity" that I have found particularly
useful. It's called by some number of names, stereo, sound-stage, and the
like. Close your eyes and listen to a room with some sounds in it. For most
folks, our brain and the shape of your ears will allow you to literally
hear the direction of each sound, with some unconsciously learned clues to
distance. A blind person can describe these, and needs them to cope with
life.
To get it there are a few requirements:
1) *T**wo frequency and phase-locked identical receivers, listening to two
different antennas. *This is taken care of in K3, K3S with the second RX,
and K4D. I can't speak to the Japanese brands.
2) Both RX set at same tone, bandwidth, with same selectivity curvatures.
In the K3 and K3S this means listening on identical roofing filters in main
and sub RX.
3) Each RX has RF gain set so antenna background noise from
its connected RX antenna is at equal levels.
4) AGC in both RX is set basically to reduce only when personal ear
loudness tolerance is approached, otherwise for weak signals as much as
tolerable like no AGC. You can run regular AGC right down to RX noise, but
the perceived spatial separation is severely degraded.
5) Headphones are required, to get rid of room audio reflections, and to
place RX1 audio only in left ear, RX2 audio only in right ear.
What you will hear is a sound stage, spread around, according to your
brain, from 90 degrees left to
When this is working right, a CW signal down in the noise will be a point
source somewhere in the front 180 degrees. The noise will be spread all
around the 180 degrees. And, in the same way we do in a crowded, noisy
cafeteria, we can (most of us) hear the person across the table from us
clearly, our brains magically use the phase differences in the two ears to
pick out the desired sound.
Back to diversity radio... In my own testing of sound stage diversity
reception, I'd say that this is sometimes equivalent to the distant station
adding a 6 dB amp. This is a highly anecdotal, impression-based
specification for sure, and it *is *"sometimes".
By itself sound-stage diversity doesn't help with QRN. *B*ut make the two
RX antennas have divergent-aimed patterns and significant RDF, and even QRN
is minimized. In your brain usually the QRN is moved to one side or the
other of the sound stage. That's why (effectively) no AGC until approaching
comfortable sound level limit is important for best sound stage diversity.
I have this working grand in my K3. The audio improvements in the K4D only
make it better :>)). But I'm still diddle-twiddle in my new K4D, trying
to get all the new stuff into muscle memory for contest wee hours when my
brain has gone soggy.
This gets to K9AY's (correct) analysis of deep fades. Given the usual
separation of two distinct antennas used for RX, the point source CW note
just wanders back and forth on the sound stage without disappearing, unless
the nulls on the ham's property physically hit both antennas at the same
time. A deeply faded signal in a one radio setup just drops out.
In a sound stage diversity, the CW signal just wanders left and right on
the sound stage.
Another benefit, if the pile-up is azimuth diverse, then they will be
spread around the sound stage. I can hear that in the K4D because the K3
pile-up muddle is gone.
When with no RX antenna, the K3 subRX was on the 40 meter dipole. The main
RX was listening on the TX antenna, a 160 L over FCP. There were many times
when I could not decipher a signal on either the 40 or 160 antennas by
themselves, but could with the K3 diversity. That has improved to some
degree with the K4D.
Just my $3.47.
73, and a great holiday season,
Guy K2AV
On Fri, Dec 20, 2024 at 2:23 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 12/20/2024 10:53 AM, Mark Lunday wrote:
> > Sounds like a great justification for diversity reception, which I can
> do on my 7610.
>
> It's exactly why diversity reception was invented, probably more than
> 100 years ago! The fundamental concept is that there must be two
> receivers, one fed to only one ear, each radio fed by a different
> antenna as widely separated as practical, so that when the two signals
> are most out of phase at one antenna they will be more closely in phase
> at the other.
>
> It's most effective (that is, easier to copy) if the two receivers are
> phase-locked to the same frequency, as is done in Elecraft radios, so
> the frequency of the CW note is the same in both ears. It produces a
> strong characteristic "stereo effect."
>
> They can also be antennas with have different directivity, either
> vertically or horizontally. Whether on topband or at VHF/UHF, the
> different paths can be arriving from different directions, or from a
> lower or higher vertical angle.
>
> Note that two antennas into the SAME receiver is NOT diversity
> reception. Some mfrs of rigs, especially SDRs, are doing this, and
> calling it diversity. It's not.
>
> 73, Jim K9YC
>
>
>
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