Re: CW/Morse keying detection revisited

On Aug 29, 11:19 am, "John Barrett" <john.ae...@xxxxxxxxxxx> wrote:
"John Hadstate" <jh113...@xxxxxxxxxxx> wrote in message

news:469e82c7-4892-4e78-bc2b-f86828849ba7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Aug 27, 12:51 am, "John Barrett" <john.ae...@xxxxxxxxxxx> wrote:





I'm working on a CW/Morse demodulator/detector/decoder that takes 8khz
16bit
audio from any SSB reciever, and attempts to detect the state of the
signal
(key down, key up) at 700hz. The current "circuit" (all software DSP on a
PC
in C#) consists of a sin/cos converter to IQ running with 700hz sin/cos
signals, followed by a 300 tap 50hz LP FIR on I and Q, with integrated
decimation to a 500hz sample rate.

I tested this setup using a synthesized on-off keyed 880 Hz. Morse
signal at 15 WPM (dot length approximately 15.75 msec).  I tried
several variations including 64-tap FIR and 300-tap FIR low-pass
filters, corrupting the signal with white noise at -10 dB, and varying
the I/Q generator's NCO from 860 to 900 Hz.  In all variations, the
magnitude of the I/Q signal perfectly reflected the keying with almost
zero noise evident in the detected signal.  The 64-tap FIR produces a
cleaner signal than the 300-tap FIR due to less ringing.  No post-
detection filtering was indicated.

This series of tests vindicates the theory of what I understand you're
trying to do.  If it's not working, my guess is that you've got one or
more implementation errors.

Did your test include a decimate to 500hz sample rate after the filters ??

No, I was looking only at the pre-decimated output of the detector.

.

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