To: | [email protected] |
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Subject: | VLF: 8270 Hz BPSK |
From: | [email protected] |
Date: | Mon, 29 Dec 2014 12:10:05 +0100 |
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Reply-to: | [email protected] |
Sender: | [email protected] |
Paul, Von: [email protected]
Gesendet: 24.12.2014 16:08 An: [email protected] Betreff: Re: Re: VLF: 8270 Hz BPSK Paul, Markus, OK:, new constellation: Code:Rate 1/18 K = 25 TX time: 11:00 to 16:00, day: when the WX will be fine. Uwe/dj8wx Von: [email protected]
Gesendet: 22.12.2014 21:59 An: [email protected] Betreff: Re: VLF: 8270 Hz BPSK Uwe wrote: > I would prefer Rate 1/8K = 25 out of your convolution code > message generator, i.e. 560bits in 4h40min. Your last transmission I think was on 2014-11-07 and I just examined the recording: You were S/N 14.7dB in 278uHz between 12:00 and 14:00. Signal is strong enough to send data quite fast. You could use 14 second symbols to send 10 characters (800 signal bits in 03:06:40) for a virtually certain decode. A more challenging test with 11 second symbols would still have 95% chance of correct decode. So far the best radio amateur message transmission at VLF was by Markus DF6NM on 2014-05-18 when he sent 14 characters across 1028km. If we use product of distance and characters as a metric then that's a score of 14392 kmchars. At 762km you would have to send 19 or more characters to beat that. Daytime should allow a 4 hour message without trouble. Rate 1/8, 11 second symbols, 21 characters (1328 bits in 04:03:28). Avoid the terminators. Send around midday +/- 2 hours. On 2014-12-14 I wrote: > http://abelian.org/vlf/tmp/141219c.png > From 00:00 to 08:00 it averaged 12.6dB S/N in 278uHz, 0.14fT. > That's enough signal to send 27 characters at a rate of 22 > information bits per hour. I gave this a test using a recording of W4DEX carrier from that night. Modulating the recording with a BPSK message 27 characters long, rate 1/16 K=25 with a symbol period of only 7.5 seconds and it decoded correctly with a small margin to spare. 9 second symbols decoded with plenty of margin. -- Paul Nicholson http://abelian.org/ -- |
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