[Elecraft] Re: CW Listening Tones

[Wayne Burdick]

"James R. Duffey" wrote:

> There is some very nice data in a psychological (physiological?) study that
> shows the ear's ability to distinguish between tones is a function of the
> frequency of the tones.

Independent of the "aging operator" theory, there's an intuitive interpretation
of why a serious CW op might prefer a lower pitch on receive. Consider two
signal separated by only 10 Hz. If one is 1000 Hz and the other 1010, the
difference between the two is just 1 percent. But if one is 500 Hz and the other
510, the difference is 2 percent. I haven't tried this under controlled
conditions. But based on on-air experiments, it does appear that when two
signals are close-spaced and interfering with each other, tuning them to a lower
pitch improves copy. (The K2 facilitates experimenting with this since you can
set up two filters with the same bandwidth but widely spaced BFO frequencies.)


> Having said that, another consideration in receiver design is the steepness
> of the crystal filter slopes. As one reduces the center frequency of the
> bandpass, the requirements for opposite sideband rejection become more and
> more stringent. The use of a 700 Hz side tone in a rig with simple filtering
> improves the opposite sideband rejection immensely. It probably has less
> effect on a rig with a good filter like the K-2.

This is an excellent point that applies to some inexpensive QRP rigs *and*
certain large desk-top rigs from the past. If a manufacturer knew they had poor
opposite sideband rejection, it was to their advantage to move the sidetone
pitch up. This may have had something to do with 700 to 800 Hz becoming the
industry standard.

73,
Wayne
N6KR