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Re: VLF: EbNaut transmissions on lower frequencies?, pre-tests: 6.47kHz

To: [email protected]
Subject: Re: VLF: EbNaut transmissions on lower frequencies?, pre-tests: 6.47kHz
From: DK7FC <[email protected]>
Date: Wed, 11 May 2016 10:58:42 +0200
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Hi Paul, VLF,

Is everything all right?
I'm asking myselfe if you are working on the decode all the time or if you are doing completely other stuff now ;-) Maybe we need more experiance with this 46km band. Maybe it is not so easy, not just 20lg(8.27/6.47) db harder.
This morning the QRN is very low, a pity that i have not been on the
air. I need to and will prmodify the system so i can transmit during
working days, i.e. all the time. Then it could be useful to start with
shorter messages during the morning hours. For example, 40s symbols and
3 characters. Or 3 characters with 200s symbols.
I was wrong when saying i am output transformer limited. Yesterday i
tested my VLF PA on a 1 kOhm (that's the loss resistance of the antenna,
about) / 400 W resistor and watched the voltage wave form at 280 mA
output current. Also watched the supply current and eventual ferrite
core warming. To my surprise it is no problem to go down to 2.97 kHz,
the target frequency :-) So it must have been a problem of the
non-resonance of the antenna.
I hope to make the system ready for 24/7 transmissions today and will
announce further experiments then.
73, Stefan

Am 08.05.2016 21:18, schrieb Paul Nicholson:
> There was another carrier from 09:45...19:45 UTC today [7th]
> on 6470 Hz.

Thanks, that was useful against the low daytime noise.

I'm having fun with the H field rx, it's not working so
well at 6.47 compared with 8.27.  E field is doing well.
At 8.27 usually H has the better S/N but not so at
6.47 I think because of the hum harmonics reducing
the blanker effectiveness.  The above carrier helps
with diagnostics.

> Start time: 07.05.2016   20:00:02 UTC
> Period: 100s
> Length: 19
> CRC 16
> Coding 8K19A

A problem with the E-field rx here may disrupt that.
Battery went flat today while I was out. Lost about
3 hours.   No a disaster, EbNaut can still recover
the message if the rest is received well enough.

It was a very noisy night last night and geomagnetic
disturbance this morning.  Maybe today and tonight will
make up for that.

Paul Nicholson

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