Message-ID: <001601c4f903$09750aa0$c401a8c0@quaycustomer>
From: "Vernall" <vernall@xtra.co.nz>
To: rsgb_lf_group@blacksheep.org
References: <84LVRMIKJB6OJ4Y8295SN42APO3VKE.41e59320@Charlie_Drake> <009301c4f8f8$a2587320$122f8351@w4o8m9>
Date: Thu, 13 Jan 2005 13:01:29 +1300
MIME-Version: 1.0
Subject: Re: LF: Audio Filters
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hi all,

I'm parallel to Jim M0BMU for regarding that QRSS reception via a sound card
does not benefit from very narrow analogue filtering in the radio, or at
audio prior to application to a sound card.  A QRN spike causes ringing and
nonlinearity in a receiver, and effectively subtracts from the remaining
time when the noise to signal ratio is still satisfactory for Argo (or
whatever FFT software) to grind out a useable result.  QRN can also cause
AGC hang.  The least "outage" resulting from a QRN spike is with other than
very narrow (analogue) bandwidth ...

My QRSS DX receiving setting options are (I use a TS-850SAT):
- IF noise blanker active (clips the spike at a system bandwidth of 16 kHz
or so)
- AGC on fast setting (quickest recovery following a spike)
- IF bandwidth 270 or 500 Hz (and wider could be a tad better still?)
- no outboard audio filtering before the sound card (thus no added ringing).

73, Bob ZL2CA

----- Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, January 13, 2005 11:45 AM
Subject: Re: LF: Audio Filters


> Dear Gary, LF group,
>
> The FFT process of the spectrogram does a very good filtering job, and the
> sound card audio input has a surprisingly good dynamic range, being able
to
> cope with unwanted signals maybe 70dB or more stronger than the wanted
> signal (at least, on the sound cards I have tried, which are nothing
> special). The limiting factors usually seem to be distortion in the RX IF
> and audio, and audio frequency hash which gets into the sound card from
the
> rest of the computer; unfortunately an external audio filter is not much
> help with either of these. I find that using a very narrow IF or audio
> bandwidth usually worsens the effect of QRN, something in the range 200 -
> 1000Hz seems best. Where a very narrow bandwidth external audio filter IS
> useful is for aural CW reception in the presence of QRM such as carriers
or
> other CW signals.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>