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[TenTec] Re: RX-340 and Noise Reduction

To: <tentec@contesting.com>
Subject: [TenTec] Re: RX-340 and Noise Reduction
From: jimr.reid@verizon.net (Jim Reid)
Date: Thu, 14 Feb 2002 09:13:33 -1000
Hi again,

Well,  later today should know what the Timewave
599zx does for the 340.  UPS site advises it is already
on a delivery truck here on Kauai,  from HRO in two days.

Anyway,  have learned  a bit more about the audio noise
level from the 340 -- the amplitude is AGC dependent!
With the 599zx I think I will be able to measure the actual
audio amplitudes,  I hope also of the noise.  In FAST agc,
the noise output is "considerably" louder than in SLOW,
and a bit louder in MEDIUM agc.  Carl,  N4PY has an 
explanation as follows:

" At slow agc, the gain will set itself to the peaks of the random 
noise.  At fast agc, the gain is constantly varying at a very fast 
rate giving a higher average gain value and hence more noise."

Well,  I never noticed this with my FT-1000D which had fast,
med,  and slow agc.  But the 340 AGC is DSP generated,  not
just feedback from the product detector to the IF stages.

The companion Pegasus in this system does have DSP noise
reduction,  which is spec'd to be about 15 dB;  it works,  but
causes distortion to SSB signals.  The FAST agc setting of the
340 makes SSB copy very unpleasant;  huge noise between
every word spoken on low level signals.  I have checked this
on both SSB and CW modes and across the  IF bandwidth
selection options available in the 340.  Once the BW is below
about 300Hz or so,  the impact of the FAST agc to noticeably
increase the noise amplitude is down.

What I hope to yield from the zx with the 340 is:

1.  Lower noise,
2.  Auto notch to eliminate heterodynes in crowded SSB bands,
3. More constant audio levels via the rumored super agc of the zx.

Am told the NR function in both Omni VI+ and the Pegasus
follows the product detector,  so is totally an audio "base" band
function;  in the 340 I wonder if NR can be included in an IF
DSP firmware revision -- don't know,  but ought to be able
to subtract non-coherent from coherent content even at
the relatively low final 340 IF of  16 2/3rds kHz at which 
A/D function into the DSP occurs and returns via D/A.

Be nice if possible to add to the 340.  

Have also been told about a product: the "Clear Speech"
loudspeaker.  Anyone know how this works,  believe it
is not a DSP device,  but some other technique to reduce
noise levels.

Will advise results later about my 340/zx experiments.

73,  Jim  KH7M

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