Monday, March 26, 2018

WQ6X SOUND PROCESSING: Stereo-CW - it's EASIER than You Think


WQ6X's loaded FT-1000mp + two QF-1A Filters
It was last summer when I came up with the idea to put together a bunch of the BEST external audio sound processing circuits in one box.  Altho the Yaesu FT-1000mp is loaded with knobs and goodies, there can never be enough for me. Since last summer, I have been combing back issues of QST & 73 magazine, picking out the ideas
I like; kind of like going to a fabric store and purchasing cloth and patterns allowing you to cobble-together your own unique
designs and expressions.

First and foremost in nearly every design I contemplate is the fact that it MUST give me more switches to throw and knobs to twiddle. It's no secret I love to knob-twiddle, Knob-twiddling during contest activities helps alleviate boredom and at least gives me the illusion that I can improve reception for each individual signal, by resolutely twiddling
the correct order of knobs,

When writing each installment in this audio-filter BLOG series, as
I introduce each circuit possibly I will include a reference to the
article(s) consulted to make that circuit happen, even if I significantly deviated from the original design; as will be the case in this article.


Stereo-CW Concept

 
Have you ever heard of Stereo CW? Neither had I until I accidently came upon an article in 73 Magazine (March 1976) by Robert Anderson (W8KZM) on this very subject. The idea is to provide an extra measure of QRM rejection by way of the space discernment "circuitry" resident in the parietal lobes of our brain.

As you can see from the original circuit, the idea is to run the audio through an LP (low-pass) filter centered on 800hz to 1000hz for the Left Ear and an HP (high-pass) filter centered on 1000hz to 1200hz

for the Right Ear. The actual audio frequency of each signal will determine which ear you hear it in.


Original Stereo-CW Circuit

Tones around 1000hz actually seem to "appear" in the "middle" of the listener's experience. As you tune through a signal (from high pitch to low pitch) the signal will start at the "far right" of one's experience, shifting "thru your head" over to the "left side" of your experience. Anderson ran the radio audio through his high powered stereo speakers for some dramatic effect(s); especially if you add in echo/reverb.

Anderson also made reference to a little known technique known as
a center channel (or 3rd channel); essentially a 3rd speaker slipped electrically "between" the left and right channel speakers. With a center channel you can TRULY experience wall-to-wall receive audio.

For my particular use in WQ6X portable operations it occurred to me that I already HAVE the LP and HP filters, in the form of a pair of outboard Autek QF-1A filters; an advantage being that they are tunable (variable), whereas the filters in the Stereo-CW circuit
are FIXED (in relation to Frequency and "Q").


WQ6X's QF-1A Selection schematic

So in fact, all I REALLY need is the stereo balance part of the original circuit; and while I'm at it, a pair of LEDs to indicate relative positioning (Left .vs. Right).

While waiting for components to arrive, I conducted a simple experiment. Using a sound generator on my laptop for a signal reference, I peaked the left-ear QF-1A at 800-hz and the right-ear
QF-1A at 1200-hz. Listening to CW signals using the LSB approach, tuning a signal from high pitch to low did indeed shift the signal from right ear to left ear until it "disappeared" on my "left side". Tuning from low pitch to high shifted the signal from the left ear, thru my head, to the right side and eventually, up-up-and-away.



The FT-1000mp has a front-panel AF-REV (reverse) button for swapping left/right channels.

Now, when listening to signals using the USB approach, tuning UP in frequency from high pitch
to low shifts the signal from left ear to right.

Of course without the AF-Rev it will shift from
right to left as it did originally.





FT-1000mp Dual Volume Controls

With the FT-1000mp, controlling receiver audio separately for VFO-A & VFO-B has been the way I've always done it.

Then, I noticed pictures of the ICOM 756 PRO III showing concentric volume/balance knobs for their approach to dual-receive.

Studying the 1000mp operators manual I discovered a firmware setting (Menu Item 4-9) wherein the Yaesu radio can be configured just like the ICOM.



AF-Gain Menu Settings

Now, without soldering
a single wire or using
a single IC-chip, I am able
to duplicate the Stereo-CW concept described in the original 73-magazine article.

The QRM fighting advantage afforded by stereo-CW is truly magnificent.



For fun and excitement, when the dual-ganged 2K pots arrive from RadioShaft.Com, I will devise the QF-1A selector circuit (diagrammed above), just to say I did, and to make the Stereo-CW available for any receiver I wish to route through the QF-1A filters.

As you can see, there are a lot of novel ideas that can be cobbled together giving us superior QRM-immunity, sometimes without spending any money beyond the equipment we already have.
This article is a representation of one of the many ideas I have
been playing around with.



MFJ 752-B (Above) + MFJ 752-C (Below)

In future articles on audio processing I will detail how I use outboard MFJ-752's and the JPS NIR-12 to process laptop audio when I run NX6T (in Fallbrook) remotely from the SF bay area.  I will also detail how I incorporated an MFJ CWF-2 filter INSIDE of the MFJ 752-B
for added CW selectivity.

Do YOU process receive audio in a unique way.
Write me and share your comments.

I would love to try out your ideas and write it up as another
installment in this BLOG series.

You can e-mail me at: Ron @ WQ6X.Info
 

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