John:
I don't think there is any problem with the PRO III's attenuation of
products outside the passband. The problem seems to be the DSP producing
products of it's own outside the audio passband. I am just using the PC
sound card to look at them. No expensive scopes here but it really
wouldn't matter in this case since you can plainly hear the noise
through the rig's speaker anyway.
N4LQ
-----Original Message-----
From: JS <john.seney@gmail.com>
To: tentec@contesting.com
Date: Mon, 27 Dec 2004 06:35:14 -0500
Subject: Re: [TenTec] Decision Made/PRO III
> >Don't do anything hasty about the ICOM PRO III until you hear from
> >my experience, which isn't quiet complete.
> >I bought one from AES and ran some Spectrogram patterns on the
> >receiver. Mine has serious problems at narrow BW settings, namely
> >huge noise spikes, far out of the passband.
> >I sent it back to AES along with a print of the problem. They will
> >either send me a replacement or a refund. I have a feeling it's a
> >design flaw but I must give them a chance to check it out.
> >Meanwhile, see this link where I compared the PRO III with an Omni
> >VI+. The picture was taken during last week during heavy QRN on 80m.
> >Both rigs set for 250hz with their noise reduction turned on. The
> >Omni was very quiet while the PRO III was making horrible clicking
> >sounds as if it were converting the static to wide band transients.
> >http://www.webham.com/Noise%20Pulses.jpg
> >Steve N4LQ
>
> Hi Steve:
>
> That is an interesting screen shot. I am curious which model scope
> you use and how
> you set it up.
>
> My first impression was that the Pro III was noisy and passing
> signals probably way out
> of its passband. Perhaps this is a DSP distortion due to radio
> settings such as too much RF gain,
> AGC, NR. It would be neat to see simultaneous scope screens with
> each radio receiving
> (or attempting) the same signal in the presence of the same noise.
>
> I own a 756 Pro 2 and have weekend access to a LeCroy scope. I tuned
> to 3512 kHz last night
> and did Power Spectrum FFTs (F1 top trace) and then did an additional
> math traces (F2 bottom) of
> the roof data (peak and hold) of the FFTs so I could see envelope of
> maximum FFT values.
>
>
> http://www.qsl.net/wd1v/LeCroy.jpg
>
> The Pro 2 is showing > 30 dB - typically 45 dB of attenuation outside
> of its 250 Hz wide passband. The full dynamic range is limited by the
> LeCroy's 8 bit front end. But since we are just looking at the
> maximum values, its illustrative for noise contours. I think the Pro
> 2 is somewhat noisy until
> I tweak settings and then it looks and sounds textbook perfect. F2
> was 40 acquisitions. Cursors
> were just to show the BW scale was the same for both traces.
>
> Maybe some of the PSK-31 waterfall display software developers will
> supply
> the ham community with tracks of signal energy vs. noise energy so we
> see the effect of
> the many adjustments we make. Most are subtle but collectively, the
> trend data could be
> very useful. The LeCroy scope can do this and its very revealing. As
> you know, the scope in the
> Icom is a fixed gain stage and you can't see your own specific
> passband. Nirvana might be automating settings to maximize S/N.
>
> 73 es Happy New Year
>
> John / WD1V
> Manchester, NH
> (Considering Orion and Pro 3, own Pro 2 and K2)
>
> --
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>
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