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Re: VLF: 8270 Hz BPSK

To: [email protected]
Subject: Re: VLF: 8270 Hz BPSK
From: Paul Nicholson <[email protected]>
Date: Mon, 22 Dec 2014 21:59:03 +0000
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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:


> 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

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