Message-ID: <001b01c33e84$1ea48710$0700000a@parissn2>
From: "Stewart Nelson" <sn@scgroup.com>
To: rsgb_lf_group@blacksheep.org
References: <000c01c33e2c$626e8840$12d1fc3e@l8p8y6> <001801c33e37$4de0b000$0500a8c0@charter.net>
Date: Sun, 29 Jun 2003 23:19:25 +0200
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Subject: LF: Re: SAQ
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Hi all,

Last year, couldn't hear SAQ, because mains frequency QRN here
(Paris 6ème) is awful.  So today, decided to try a portable radio.

Took about 36m of cat-5 cable and made a 9-turn loop about a meter square,
held in place with two mop handles and duct tape.  Wired the 8 leads in
series to make 72 turns.  Connected directly to mic input of laptop; no
attempt at tuning, balance, shielding, etc.

Took it on the Métro to Bois de Vincennes (got a few weird looks),
walked about half a km into the park.  Leaned the loop against a tree
and started recording.

It turns out that even this modest antenna was gross overkill.  The SAQ
carrier was more than 60 counts on the 16 bit A/D.  More importantly,
the received noise was more than 30 dB above the on-board sound
device's noise.

All processing was done with Cool Edit, so I could see or hear the
results after each step:

1. Prefilter to remove < 300 Hz (power QRN) and > 18 kHz (internal spurs).
2. Amplify to clip big noise impulses
3. Bandpass filter 17.0 - 17.4 kHz.
4. Mix with tone at 16.5 kHz.
5. Convert to low sample rate (this also removes mixing USB).
6. Final filter, 80 Hz wide.
7. Save as MP3.

The final result, though not as good as Christer's recording, would be
easy armchair copy, if not for the keying anomalies.  You can hear it
at http://www.scgroup.com/ham/saq-030629-0830-paris.mp3 .

Unless I missed it last year, this is probably the first time that
a Web address was broadcast world wide, using an electromechanical device!

73,

Stewart KK7KA