Topband: DX Conditions

[Jim Brown]

Thanks Guy. You're describing in greater detail what I did somewhat more 
succinctly in my two posts, and what I've been doing since the first K3 
with two receivers in 2008.

73, Jim K9YC

On 12/20/2024 1:05 PM, Guy Olinger wrote:
> Thnks, 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.