Friday, January 5, 2018

Improving Signal:Noise of CW signals by 3dB

There is a very interesting article in this month's CQ Magazine by Pete N8PR.

He notes (pun intended) that he is able to discern an improvement in copying weak signals on CW by listening to a station with both of his receiver's VFOs tuned to receive the station but with a separation between them of 65-80 Hz.

The article goes into the details of how and why this is theoretically possible, touching on musical theory of the chordal scale, mathematics of accoustics/hearing and the biology of the human ear. If the math is correct, listening to a CW signal in this way should improve its perceived loudness by 6dB and that of the background noise by 3dB, resulting in a net 3dB improvement in the signal's SNR.

Many modern rigs provide the capability of listening to both VFO's simultaneously. Unfortunately, this will, on most rigs, prevent operating split since the second VFO is being used as an additional receive VFO. Flex owners can open another pan display and use it as their transmit VFO.


I am a recent subscriber to CQ Magazine's online version and am quite happy with it. I always enjoyed perusing the magazine and sometimes buying an issue when it was available at Barnes & Noble but I didn't subscribe due to the numerous negative reviews regarding timely (non)delivery of the physical magazine to subscribers.

With the 630/2200-meter bands now available for use by US hams, and a quarterly column on those bands by John KB5NJD, I thought it was time to take a chance and subscribe to the digital version. My emailed notification of each new issue's availability is received no later than the second day of the month.

Articles like the one mentioned above are the reason I'll most likely re-subscribe.


  1. Hi John,

    many thanks for that information about it. Is it possible to get somehow the CQ Magazine original article in .PDF please? Or somewhere to download please?

    mni tks,
    73 - Petr, OK1RP

  2. Thanks, John! I haven't perused my copy yet; but I'll have to try this on the KX3 using the "Dual Watch" feature.

    1. External speaker maybe would help ?
      73's Mats sm0fpr

    2. I don't subscribe to CQ so I haven't read the article but I suspect I know what he's driving at. Here's my suggestion for dealing with the problem John mentions (again all theory; I haven't tried it but it's got to work). Don't plug the phones into the KX3 directly. I'm sure the headphone outputs are both have a fairly low source impedance if they're going to feed say 32 ohm headphones successfully. At the cost of some signal loss, take each hot side and build it out with maybe 100 ohms. Join the far ends of the two 100 ohm resistors and tie BOTH headphone sides between that point and ground. You might have to play with the 100 ohm value; too low and the amplifiers driving the headphone outputs of the KX3 won't like it, and too high and volume will drop too much. To avoid the latter, you could build out with much higher values than 100 ohms (and then the amplifiers inside the KX3 certainly won't object) and then feed from the tie point to an external audio monaural audio amplifier

    3. David, I'll bet you could just use mono headphones and that would "fix" everything, putting both VFO's in both ears.

    4. Do you mean just paralleling the two outputs and feeding that to both ears? I don't think the two amplifiers would like that. The two signals are designed to be at different audio frequencies, so each audio amplifier would load the other one with its source impedance. That's why I suggested the build-out resistors.

      David, VE7EZM and AF7BZ