[Lf] Best tone for aural copy]

[Andre' Kesteloot]

Dick Rollema wrote:

> To All from PA0SE
>
>  In an e-mail to Bob, ZL2CA. discussing the PA0LQ audio filters, I mentioned
> a thesis
> on the reading of morse code signals in noise.
> As a result Bob asked:
>
> > Do you know a way of accessing the university and thesis details?  >
>
>  I gave the following reply which I also sent to the reflector because
> others
> may be interested in it.
>
>  Bob,
>
>  The thesis has the title "Signal detection in noise, with special reference
>  to telegraphy".
>
>  The author is Peter Montnémery, SM7CMY, who is employed at the Department
>  of Otorhinolaryngology [say that fast ten times :-)],  Head and Neck
>  Surgery, University Hospital, Lund, Sweden. Code number is
>  ISRN LUMEDW/MERL -- 1038--SE.
>
>  Some of the subjects treated are:
>
>  1. Recognition of telegraphy disturbed by noise at different S/N-ratios and
>  different telegraphy speeds.
>
>  2. Recognition of telegraphy signs at different listening levels and
>  frequencies.
>
>  3. Effect of dichotic presentation on the recognition of telegraphy
> signals.
>
>  4. Recognition of telegraphy in hearing-impaired telegraph operators.
>
>  5. Performance of electronic morse decoders in decoding telegraphy masked
> by
>  noise.
>
>  6. Detection of trains of tone pulses masked by noise.
>
>  I learned about the thesis by a message from Peter Schnoor, DF2FL, via the
> LF-Group reflector, considerable time ago.
>
>  Via a friend at the Leyden University I managed to obtain a copy which took
>  many months to arrive.
>  After writing an article about it for our VERON magazine "Electron"  (still
>  waiting to appear) I have passed it on to my good friend PA0CX/F2ZI who
> will
>  or already has sent it to Pat Hawker, G3VA.
>
>  > As a further aside, do you know why Harry picked 1000 Hz for his filter?
>
>  I don't know.
>
>  For my filter I had to use 1000Hz because my German LF-receiver of the
> sixties has a fixed BFO that produces an audio note of 1000Hz when the
> signal is centred in the IF filters.
>
>  But when I am busy in my shack doing other jobs I often leave the receiver
> on with a wide IF-filter selected, no audiofilter and such high volume
> that the headphones function as speaker.
> I  have noted several times that I could detect a weak signal this way.
> After putting on the headphones and switching on the 30Hz audio filter it
> was often very difficult to read the signal!   It again goes to show that
> the ear-brain combination acts as tracking bandpass filter that should not
> be "assisted" by too much pre-filtering.
>
>  73, Dick, PA0SE