[TenTec] Binaural CW experiment No. 2

[Jerry Volpe]

[Not intended for Orion or Orion II owners who have built in binaural CW
reception capabilities, but for the rest of us who slug it out with
pre-Orion gear]

The HF portion of my 'shack' has nine Ten-Tec transceivers ranging from
the Omni-VI+ to the most basic Century 21 (yes, my wife knows I am
crazy). Love the heck out of all of them and I love to dabble into new
ways to put them to work. And although I operate numerous modes, CW has
become a growing passion these past few years. Trouble is sharp crystal
filters (and I have all filter options installed in my Ten-Tec rigs)
tend to create audibly harsh sounds to me which quickly result in
listening fatigue and headaches.... so I am always looking for ways to
separate CW signals without having to use the sharpest filters. Some
months back I shared details on a small add on audio filter project for
'Binaural CW, or Stereo CW" reception (basically a few op amps,
resistors and capacitors) that basically split incoming audio into two
channels -- applied one channel to the left headphone or speaker, and
the other channel to the right headphone or speaker. One channel is a
low-pass filter allowing all below 750 Hz to pass the other a high-pass
allowing all above 750 Hz to pass. I thought it was a simple project
that many could have fun with and it used readily available parts, and
truthfully many did show interest.... but few were into building,
especially without purchasable kits, so that project ideal basically
ended there.... although I still use the filter I built (please check
reflector archive... do search on  "Binaural CW" for details). Now
please note that I am not taking credit for inventing binaural CW
reception... just dusting off a few great ideas that are not in the
mainstream....

Anyway, I enjoyed my binaural filter project because it was simple,
inexpensive, and ultimately very effective. It had two major
shortcomings though: I could have chosen better quality op amps for
better distortion specs and the cross-over frequency was fixed in
hardware. Hmmmmmmmmmmmm.

 If you haven't taken time to listen to binaural CW and CW is your mode
I highly recommend it. Just remember, when using this approach you don't
crank in your sharp IF filters, rather you leave them at 2.4 or 1.8
kHz.... maybe you could go as tight as 500 Hz but I wouldn't recommend
it. With binaural CW you are letting your head separate the signal you
want from what is nearby to it. You hear what you want in the 'middle'
of your head, signals higher in pitch more to one side, lower in pitch
more to the other side. That broad banded noise that accompanies the
signals is split into high and low components as well which tends to
make it appear far less in overall amplitude. Of course many of us
haven't learned to filter in our heads or if we had in the past we have
more or less lost much of that ability after years and years of sharp,
single signal crystal and DSP filtering.

_________________________________
Binaural CW Experiment No. 2
[you like to employ gadgets that already exist rather than build]

In my latest experiment in binaural CW reception I use a Crate brand 31
Band Pro Audio Equalizer (LS3-231) that I picked up used but in great
shape for about $60 plus shipping (really). It has 31 1/3 octave filter
bands for left channel equalization (plus or minus 12 dB each) and 31
1/3 octave filter bands for the right channel; channel independent
variable low-cut from 15 to 240 Hz and variable high-cut from 3 kHz to
40 kHz; separate output level controls; and front panel bypassing.  This
equalizer supports both balanced and unbalanced audio interconnects for
inputs and outputs as well as the facility to 'float' the internal
ground of the equalizer. Anyway, this is a $300-$400 equalizer and I was
thrilled to get it on my more restrictive 'ham' budget.

Adding the Crate dual channel equalizer into my transceiver's output
audio (to split and shape my CW audio for binaural reception) was a very
easy task for me as for the past few years I have used a Mackie Micro
Series 1202-VLZ, 12- channel mixer to process the audio output of all my
transceivers and receivers. These 'Pro' line mixers are plentiful in the
used market, reasonably priced and highly capable. There are less
expensive mixers available too. Many hams use Behringer brand items and
that company has  4, 6, 8, and 12 channel mixers that sell for $50 -
$100 new. Of course there are other brands as well. Anyway, without
getting technical, nearly all of these mixers have 'AUX SEND and AUX
RETURN' functions that basically let you reroute one or more of the
audio mixer channels to an external 'effects' device and then bring the
manipulated sound back into the mixer and then out to your speakers or
headphones. The cool thing here is that the AUX SEND is mono but the AUX
RETURN is mono or stereo! So I made up a balanced audio 'Y' cable that
took the AUX SEND to both the left and right channel inputs of the CRATE
equalizer and then made balanced audio cables  to return the separated
left and right equalized audio back into the left and right sides of the
AUX RETURN. It was as simple as that. Another nice thing about this
CRATE is that it has connectors for XLR, 1/4 3-conductor phone (both
balanced) and RCA connectors (for unbalanced). The Mackie, like most
Pro-line mixers, supports balanced or un-balanced audio connections. To
avoid any possibility of ground loops as well as to eliminate yet
another spot to introduce RF into the mix, I chose to use balanced audio
interconnects.

How does it work? Cool! I am still having a great deal of fun
experimenting with the equalizer settings but basically I crank the Low
Cut up to 250 Hz for both channels and the High Cut down to 3 kHz for
both channels as well. Then on one channel I cut out all bands (down to
-12 db) except for 315 Hz, 400 Hz, 500 Hz, 630 Hz, and 800 Hz. Basically
I slowly curve up the audio from 315 to 800 Hz which I set to +12 dB.
Then on the opposite channel I cut out all bands except for 800 Hz, 1
kHz, 1.25 kHz, 1.5 kHz, and 2 kHz. I set 800 Hz once again to maximum
gain of +12 dB and then slope the others down. As a result my desired CW
signal (the one I am zero beat to) is equal in both speakers or
headphones and the lower pitch signals are in one side and the higher
pitched signals in the other (noise is split too). When you add together
the 24 dB of band equalization range with the master Low Cut and High
Cut controls you can create a very selective set of independent audio
filters.

Other uses? Of course. This setup can be used to finely tailor audio for
any mode, including sideband! A certain well known manufacture of
inexpensive ham radio related gadgets offers an audio 'Sound Enhancer'
for around $179 that has but a few bands of equalization without the
ability to adjust independently for each ear! Imagine that. As we get
older our hearing perception changes but do our ears necessarily change
in exactly the same way? I don't think so... so it seems kind of silly
to make an audio enhancer that doesn't allow you to enhance the signal
for each ear independent of each other. My approach allows for that.

__________________________
Why Balanced Audio Interconnects?

[I am purposely not getting technical here]
1. Reduced opportunity to introduce additional ground loops, hence no
additional 'hum'.
2. Greatly reduced susceptibility to RF pickup and this is generally a
very good thing.

With balanced audio interconnects your audio signal is separate from a
common or chassis ground. There is a + or hot audio line and a - or cold
audio line. Typically they are twisted together and encased in a
separate shield. The shield does not contain any audio information or
act as a return path in any way. In fact, the shield is usually
single-ended meaning that it is connected to only one of the two
interconnected devices. This single-ended shield connection stops the
introduction of a new ground loop path but maintains a ground path for
any stray RF introduced on the surface of the shield conductor
(remember, externally picked up RF travels along the outer skin of the
shield and does not normally 'leak' into the inner wires if there is
good overall shield coverage). Now having the audio itself run along two
balanced and twisted conductors is a cool thing. Audio on the two wires
are naturally out-of-phase by design and travel along unimpeded. Local
noise coupled onto the wire pair, on the other hand, is in-phase and
will therefore cancel itself out in the receiving device's 'balanced'
input stage. So if AC hum or RF should get through the shield onto the
twisted wires what ever is picked up is cancelled and only the 180
degree out-of-phase desired audio signal remains.

You may notice that certain high end transceivers are appearing with
'XLR' type microphone connectors. Not to repeat myself too often but...
this is a good thing. Far too many of us fight the RF daemons
inadvertently introduced into our transceivers from the unbalanced
microphone (and direct audio inputs.... PSK-31, RTTY, etc.). And of
course the problem gets worse with increased length and when we
introduce devices between the microphone and the transceiver (microphone
noise gates, audio equalizers, voice keyers, etc. ). If our equipment
design allowed for balanced audio interconnects on all inputs and
outputs we could, with reasonable care, predictably greatly reduce if
not eliminate stray AC hum and RF pickup in our shacks. Nirvana!!

So, like I mentioned, when we see new rigs come out with XLR microphone
connectors this is potentially a good thing (Ten-Tec Sales and
Engineering please take note :)  )

Have fun &
73,
Jerry, KG6TT
Fairfield, CA