For those who might be interested: Kanga US sells a kit for a stand alone binaural receiver:
http://www.bright.net/~kanga/kanga/KK7B/biqr.htm This is not an endorsement of any kind, and I am not affiliated with Kanga US. The page is interesting though, because it contains a link to the original QST article describing the receiver. 73, Mike ----- Original Message ----- From: Jerry Volpe <[EMAIL PROTECTED]> Date: Thursday, May 25, 2006 2:35 pm Subject: [Elecraft] Re: Binaural CW Reception > I have done a couple of Binaural CW reception projects and found the > results very appealing. Let me begin by sharing a few thoughts: > > 1. With binaural reception you normally would NOT use tight CW > bandwidths as the object is to allow more audible information to > be processed by our brain. I think that you would want at least > 600Hz or > greater. I typically use a 1000Hz type filter or wider but generally > nothing tighter. A stereo 'soundscape' is created within your head > withthe primary signal (the one centered in the Binaural filter) > appearingin the center of your head, and the ones higher in pitch > progressivelyoff to one side and the ones lower in pitch off to the > other side. > 2. Due to the sound dividing by frequency you notice only the lower > frequency background 'noise' component in one ear and the higher > frequency component in the other. It is surprising how much LESS in > intensity the noise is overall than what it was with combined > energy to > both ears. This alone is worth the price of admission. > 3. Many of today's CW operators have not trained themselves to use > theirown brain as a CW filter and instead rely on very sharp band-pass > filters for single-signal reception. Binaural CW reception provides > multiple signals which many find too confusing. > 4. Binaural CW reception should be great for NET, roundtable, and even > contesting where you often need to hear many stations on slightly > different frequencies. > > My first project was a stand-alone Binaural CW filter using a pair > of OP > Amp ICs. Basically, the audio input passed into both a low pass filter > and a high pass filter with the low and high frequency cutoffs at the > desired center frequency.... 700 Hz for example. The output of the > eachfilter was further amplified (as needed) and then applied to > eitherstereo speakers or to stereo headphones. > PRO: Small package. Simple approach. Low cost. Easy to build. Works > wellenough for a single design cross-over frequency. > CON: I could have used better quality OP Amps for lower distortion. > Theones I got were from Radio Shack (sigh). Still not bad. Can't > changecross-over frequency. This is OK if your receiver has a fixed > CW offset. > Myself, I like to change my offset to minimize long term listening > fatigue. But then again only a couple of my transceivers allow for > that.... most don't. Another CON was the fact that I had to build this > filter. It was amazing to me how many hams were interested in the > project (I posted the info on the Ten-Tec reflector last year) but > wereunwilling or unable to assemble a project without a kit. > > I think it would be wise to use two pass-band filters rather than a > low-pass and a high-pass configuration. That way you can also take > awaythe unnecessary lows... say below 300 Hz and the unnecessary highs > perhaps over 1500 Hz. These filters should not have sharp slopes as > thatwill add ringing. > > My second project began with the following in mind: > 1. Using band-pass filters rather than low-pass and high-pass. > 2. Include the ability to move the combined filter cross-over for > different CW offsets. > 3. Get the lowest distortion possible in the filtering. > 4. Use something commercially available rather than 'build your own'. > > My first thought was to obtain two SCAF audio filters (highly > programmable as far as band-pass characteristics, no ringing, low > distortion). SCAF filters are not too expensive (you need two) when > found used. I have seen them sell for around $40 to $60 each. However, > before I found the two filters I decided t use another approach > using a > 62-band, two channel, Pro Audio equalizer. The one I obtained (for $65 > used!!!) was a practically new Crate LS3-231. With this approach I can > move my cross-over frequency as desired and have good control of the > high and low frequency roll-offs. Distortion is negligible. I would > notrecommend this approach with a typical home stereo equalizer as the > filter quality is not good..... the band separation is poor.... and > youdon't typically have near enough bands (the Crate has 1/3 octave > bands)to allow selection of the appropriate cross-over > frequency.... and I > doubt they hold up well in a high RF environment. Anyway, I am > currentlyusing the Crate solution and it does a great job. Trouble > is I want to > use this equalizer for other types of reception so I am continually > reprogramming it. For that reason, and for a bit better cross-over > programmability, I am still planning the simpler approach using two > SCAFfilters (as soon as I find what I am looking for at a price I > want to pay). > > About DSP filters in this application: > > I know of one commercial manufacture, TimeWave, that includes Binaural > CW reception in their high end DSP filter. I had my suspicions > regardingDSP signal path delays and QSK CW operations. I obtained a > TimeWaveDSP599zx and found that the resultant binaural audio was > very good but > that the delay was as bad as I had anticipated and unacceptable for > QSKover about 15 wpm. Your mileage may vary. :) Anyway, if you > don't use > QSK or you are very casual at speed and you don't mind spending a > sizable sum for one of these filters go for it. Please note that the > actual firmware version in the DSP-599zx is important and that only > themost recent firmware's have the Binaural CW function (or so I > was told). > > Lastly, I do know that there are at least one current amateur radio > transceiver with binaural CW reception built in.... perhaps more than > one. I am talking a fairly expensive transceiver (not named) so for me > it wasn't a reasonable path to just for this extra capability when I > would make or configure binaural reception for a lot, lot less. Try > before you buy! > > 73, > Jerry, KG6TT > Fairfield, CA > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
