Wednesday, April 24, 2019

Some Further Thoughts regarding Stereo CW

           It has been quite some time since I originally shared my discovery of Stereo Cw. 
               ([CLICK HERE] to read the original article.

You don't need a dual-watch or dual-receive radio to transform your stereo headphones into an incredible operating experience.  With Stereo Cw you DO need to be ready for signals to be shifting around "inside your head" as you tune THROUGH a signal or use the R-I-T control to "position" the signal "in your head"; or, if you prefer, "between your ears".

Properly centered, tuning the R-I-T +/- 150 cycles can "position" a signal in the upper-left of my hearing or the upper-right.  With the R-I-T = 0, the signal "appears" to be "in front" of me.  At first
this takes some getting used to; then, later, you wonder how you ever ran a radio contest without it.

In the original article I detailed the Stereo Cw circuit and then suggested that we can simulate
that circuit by way of two outboard filters properly offset from each other.  For my portable setup at W7AYT's QTH I use a pair of Autek QF-1A audio filters; one for each ear. 

To enhance my operations from Alameda, I recently implemented a filter combination; an Autek
QF-1A for the left ear and an MFJ-751 for the right side.  Separate splitter cables separate the
input audio towards each outboard unit and recombine it back into a stereo cable plugged into
a wireless headset transmitter.

In the above picture, notice the QF-1A setting (for the left ear) is for HP (High Pass), while the MFJ-751 setting (for the right ear) is for LP (Low Pass).  Tuning a signal from high-pitch to low causes the signal to "move" from the left-side of my experience, to more towards the right-side.  Likewise, tuning a signal from low-pitch to high causes it to shift from my right-side, "thru my head" and eventually to the left; continue tuning to a higher pitch and the signal will seem to move to the "upper left" of my experience.

An additional advantage to using Autek QF-1A (or MFJ-752) outboard filters comes from the auxiliary notch filter those units have; the MFJ-751 possesses no such additional filter.  This secondary [notch] filter can notch-reduce a signal in the passband for that ear.  Use of these external filters takes the concept of an APF (Audio Peak Filter) circuit to the next level. 

Combine these filters with a transceiver's existing DSP configuration - either audio-based (as with the Yaesu FT-1000mp) or IF-based (as found with the Elecraft K3 and K3/0) - resulting in a double-whammy against all manner of complex
noise and QRM.

Combining analog and digital technologies allows co-leveraging BOTH methods to alleviate
a single/combined source of QRM & QRN.  Realize that every attempt at filtering audio may itself introduce its own "artifact" (QRM).  For example, "pushing" the QF-1A filter to its limit may introduce "ringing", requiring that the filter intensity be "backed off" a little.

With external audio filters adjusted similar to the above-mentioned setup, running pileups becomes considerably more DO-able; different signals with different offsets are experienced either in the left-side, right-side or "middle" of the listener's "Experience".

Stereo CW is an incredible augmentation to radiosport signal copying.  While it does nothing to boost the transmitted signal, it makes once-difficult copy copyable.  Regardless the quality of the transmitted signal, if "I can't hear 'em, I can't work 'em".

What about You?  What do YOU do to make signals more readable?

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