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DSP Noise Reduction on Receive



Hi gang,

I decided to try an experiment this afternoon and see how well my Timewave
DSP-599zx works for improving the audio SNR on AO-40 signals.  Here's what I
found out:

For the beacon, the Timewave is not very useful.  It appears that the
Timewave filter response has a suck-out right around 1000 Hz.  I'm not sure
why, but no matter how you tweak either the High Pass or Low Pass
adjustments, it doesn't take that out.  From what I can tell, it looks like
that part of the audio spectrum is needed to properly decode the beacon.

On voice Qs, the DSP works great.  The random noise reducer made the
difference between being able to hear people and not.  The squint during the
4 or 5 Qs I had was about 25 degrees.  If I took the random noise reducer
off, I would be able to tell there was someone talking to me, but it would
be pretty much unintelligible.  Even if I could copy the signal, adding the
NR would help tremendously in listening comfort.

While I have an FT-847, I am not using it in receive (using an FT-817
instead for RX) so I cannot really compare the two DSPs.  Although I believe
the Timewave is far superior.

I have ordered a ClearSpeech II base unit.  Hopefully it will be in this
week.  I plan on adding that in the audio chain and I will report on how it
helps too.  From what I remember from playing with it at Dayton last year,
it blows the Timewave's random noise reducer out of the water.

So for those of you who have external DSPs, try them out and see how much of
an improvement you get in received audio.

73,

Jon
NA9D

-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Citizen of the People's Democratic Republik of Illinois

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/na9d   <- Updated on 1/22/03!!!

"A life lived in fear is a life half lived."


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