Click here to see the original article from HR dec.-79.
Dear HR:E.H. Conklin, K6KA, is not quite right in describing the Hellschreiber as a wideband system (Comment, March, 1980). Admittedly, the bandwidth of any keyed system is a function of the keyed element rise time, but with proper pulse shaping as practiced by the majority of the PA0 and German Amateurs the amount of spectrum space occupied by a Hell- schreiber signal is only marginally greater than that of 45.5-baud RTTY.
The bandwidth necessary for Hell-schreiber may be quite easily com- puted by reference to CCIR Recommendations, which in Appendix 5 of Radio Regulations state that this is the product of baud speed times K, K being a factor depending on the "goodness" of a circuit. The baud speed of Amateur Hellschreiber is 122.5 which multiplied by a K factor of 3 gives a bandwidth of 367.5 Hz. The K factor of 3 comes into the pic- ture because it has long been recognized that a square wave and its third harmonic is perfectly acceptable for normal communications. The band- width of a 45.5-baud, 470-Hz shift RTTY computed according to CCIR is 245Hz.
K6KA is correct in his criticism of the Chinese Hell-Fax signal, lately on 14140 and believed still to be working in the Region 2, 80-meter band. But this is a different system with a baud speed of somewhere in the region of 400, and observedly with little or no attempt at pulse shaping; some channels are even FSK with 800 Hz shift They are certainly wide band and not to be compared with the Amateur 'hell' in Europe.
Finally, I hold no brief for the Hellschreiber system as such but, as I worked with the system throughout most of its active life and am fully conversant with its advantages and shortcomings, I thought I'd like to put the matter straight.