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[TenTec] Re: RX-340 and Noise Reduction

To: <tentec@contesting.com>
Subject: [TenTec] Re: RX-340 and Noise Reduction
From: n4py@earthlink.net (Carl Moreschi)
Date: Thu, 14 Feb 2002 19:46:22 -0000

Fast AGC should not be used for SSB or CW.  These modes
work best on the RX340 with slow AGC.  The slow AGC setting
seems perfect for these modes.  The fast AGC setting is so fast,
it increases the gain noticeably between words or CW characters.

I rarely find the noise reduction setting on the 599zx helps.
When it does help, it's not for random noise, but more for
man made noises such as power pole buzzes.

Carl Moreschi N4PY
Franklinton, NC
----- Original Message ----- 
From: "Jim Reid" <jimr.reid@verizon.net>
To: <DennisKT5D@aol.com>; <aa5f@hiwaay.net>
Cc: <tentec@contesting.com>
Sent: Thursday, February 14, 2002 7:13 PM
Subject: [TenTec] Re: RX-340 and Noise Reduction

> 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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