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Re: LF: NA VLF

To: [email protected]
Subject: Re: LF: NA VLF
From: DK7FC <[email protected]>
Date: Tue, 09 May 2017 15:09:39 +0200
In-reply-to: <[email protected]>
References: <[email protected]cal> <[email protected]> <[email protected]>
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Hi Joe,

Maybe you can provide some informations for us, to get a clear impression of what you're doing:
-A picture of the coil in its current location (when transmitting).
- A picture of the antenna, along with some data like, length, height above ground, sourrounding trees, antenna capacity.
- Measured coil DC resistance
- Which antenna current at which RF power?
- What is the antenna wire diameter?
- A picture of the isolators which hold the wire.

With SpecLab you can measure and monitor the antenna current, you can transmit carriers and e.g. EbNaut. You can program (or get mine) a safety function which stops the transmission in case that the current drops under a certain level. This can prevent from a fire when there should be a flash over across the coil or somewhere else. And another important function: The phase of the radiated signal is constant even when the antenna becomes detuned due to temperature changes or rain. This is realised by a capacitive feedback pickup probe applied to the soundcard input (a tool by DF6NM). The phase is compared with the phase of a SL internal signal generator and variations are corrected. So it is a PLL function. So all you need is a cheap GPS module, all other components are already in your shack...
73, Stefan



Am 09.05.2017 14:48, schrieb [email protected]:
Your efforts are greatly appreciated, Paul, along with the kind words
and motivation from Stefan DK7FC Markus DF6NM Marco IK1HSS and Luis EA5DOM.
The TX has been QRV since Sunday afternoon and is still going.
The drift is interesting -- but not desirable.  It is time to look
at Spectrum lab again and explore some ideas to increase the ERP.

Joe VO1NA

On Tue, 9 May 2017, Paul Nicholson wrote:

I can't detect any signal from Joe last night
8th/9th 22:00 to 04:00, not a trace - perhaps
the tx has gone off.

After sweeping for optimum settings, I couldn't get
much improvement.

Daytime reception, S/N = 13.5 dB in 23.148 uHz:

http://abelian.org/vlf/tmp/170509a.png

Some of the energy is in adjacent bins on this 12
hour integration, the frequency probably drifted
a little, losing a dB or so.

Nighttime, S/N = 14.3 dB in 46.296 uHz:

http://abelian.org/vlf/tmp/170509b.png

Tried an EbNaut 'decode' of the 6 hour nighttime
signal.  Unmodulated carrier is a valid message which
decodes to a string of '*' characters. Because of the
linearity of the coding, the performance is representative
of any other message with the same settings.

4 chars 16K25A CRC=12 Symbols = 22 seconds, duration 05:52:00
gives

rank 946 ber 42.2% '****'

carrier Eb/N0: -0.1 dB
carrier S/N: 13.53 dB in 47.3 uHz,
            -29.72 dB in 1Hz,
            -63.70 dB in 2.5kHz

The snag is, this 'decode' is only possible because I could
see the signal and measure its frequency.  A real EbNaut
message is invisible and if the frequency is out by more than
about 5uHz it will not decode.

5 chars should just be possible but I could not get it to
decode.
--
Paul Nicholson
--






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