[TenTec] Adding Binaural CW to Ten-Tec transceivers

[Jerry Volpe <kg6tt@tomorrowsweb.com>]

OK, I know the Orion does this and in a more sophisticated way, but 
there are many of us who don't have Orions... this info is for them :)

If you like to operate CW then you might want to consider whipping 
together adding a Binaural CW audio filter between your rig and your 
headphones (speakers are possible, see comment later).  I built my 
filter in about 4 hours, finishing it earlier this evening. I am most 
seriously impressed.

Here is the website where I found the basic circuit I worked from:

http://web.telia.com/!u85920178/

The design is from Harry Lythall - SM0VPO

Anyway without going into dreary details I am going through this 
'headache' thing where lots of stuff trigger migraines (not pleasant) 
and even though I love the floating sound of shortwave sometimes 
punching down  a whole lot of filtering to isolate a CW signal distorts 
the tone enough to be a rather unpleasant experience. The whole 
filtering down thing got me to thinking about a series of articles on 
Binaural CW in HR magazine many years ago. So after a bit of a Google 
search I came up with the notion that this was something to try. I 
didn't find too many actual circuits and only one very expensive add-on 
DSP unit providing a commercial alternative (and perhaps too much delay 
to make it practical for QSK)... I settled on Harry Lythall's circuit. 
Last night and this evening I put it together using basically Radio 
Shack Parts (well I had to dig a bit for the 39K resistors). The 
finished filter works great and I'm having a lot of fun listening to 
'wide bandpass' cw.

Basic Concept: Two OP amp filters, one low pass, the other high pass, 
split the incoming audio out to the headphone jack where esentially 
everything below 700-800 hz is heard in one earphone and everything 
above in the other. In practice you will hear the low frequency 'noise' 
in one earphone and the high frequency noise clearly in the other and 
the cw stations you are listening to more or less spread out across the 
inside of your head. This separation gives our brain more to deal with 
in identifying a particular sound which in turn makes it easy to 'hear' 
it. You actually don't really need or want to use the narrowist receiver 
filter settings when usining this Binaural external filter. You can of 
course, but it sounds far better and less constrained when you don't.

Of course you can take the output of the Binaural filter into a small 
stereo amplifier and then into two speakers one on either side of you 
and experience the spacial placements this way, but headphones are 
easier. Now, of course you have to have stereo headphones. I use Kenwood 
HS-5 headphones which are normally Monaural, but I moved two wires and 
changed the plug and now they are stereo.

One last point. In Harry Lythall's article he mentions that with some 
OP-AMPS his basic circuit may suffer from 'Crossover distortion 
problems. He suggests if this happens to place certain value resistors 
between the OP-AMP stage outputs to the +12 volt supply rail. As it 
turned out mine was horribly distorted. With a few tests I fixed the 
problem entirely by placing a 10k resistor from pins 1 to +12 volts, 
another 10k resistor from pin 7 to +12 volts, a 560 ohm resistor from 
pin 8 to +12 volts and another 560 ohm resistor from pin 14 to +12 volts.

If you enjoy CW you should try this out. I am using mine with both my 
Paragon and my Omni=VI+. As a plus you don't hear any residual 
transceiver 'hum' and there are NO delays that would effect QSK.

73,
Jerald, KG6TT
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