Re: LF: LF and VLF EbNaut

[Markus Vester <markusvester@aol.com>]

Yes for LF I would also recommend the method with signal generator, relay and ebnaut-tx software, it's really not difficult to get started. Instead of the relay, a double balanced diode mixer also works well, with the DC-coupled IF port driven directly from RS232. If you happen to have a linear PA you could optionally insert a simple C-R lowpass for shaped keying. The realtime clock of the sending PC should be steered by NTP, or alternatively using NMEA from an external GPS. 

I think that frequency accuracy needs to be much better than 5e-8. To keep the phase drift within 30° over half an hour, the frequency should ideally be known to better than 46 uHz, or about 3e-10 (0.3 ppb). Most simple OCXOs cannot hold up to that. When the signal is strong, one can sometimes still obtain a decode by aligning the slope of the symbol phase graph. But this won't work for weak signals, and poking around blindly for a frequency offset that may or may not produce a decode can be a cumbersome and frustrating affair. The best choice is a GPS derived oscillator, or a well calibrated Rubidium source. 

When will we see you?

Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Rob Renoud <k3rwr@md.metrocast.net>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mo, 10. Dez 2018 23:33
Betreff: Re: LF: LF and VLF EbNaut

Paul, Chris and EbNaut LF,

Stefan makes a good argument for trying what you have for TX.   The HP-3325A specs show a frequency accuracy of +- 5 EE-8 and stability (option 001) of +- 5 EE-6.  The HP-3325A should work ok on 2200m with a message duration of 28 minutes or less.

The 180 phase reversal is easily implemented using a DPDT relay with a 1:1 transformer connected between the 3325 generator and the amp input.  Drive the relay with the RS-232 RTS or CTS signal from the computer running ebnaut-tx.exe found on http://abelian.org/ebnaut/ such that the relay shifts the phasing of the input to the transformer.

Time and frequency are important on the decoding end.  Try to get them as accurate as possible on the TX end.

For 2200m a good starting message format is:

Code:  8K19A

Symbol Period:  3

CRC: 16

Characters: 5

Duration:  25:36.00

Repeat on the hour and half-hour

Announce your beacon and give it a try.  Lot’s of LF EbNaut listeners to let you know if it’s working out...

Comments and other suggestions are welcome.

73,

Rob - K3RWR

On Dec 10, 2018, at 15:58, <jrusgrove@comcast.net> <jrusgrove@comcast.net> wrote:

BPSK transitions cause key clicks with non linear transmitters / amplifiers. As a practical matter ... with the high Q transmitting antennas in use ... and that it's unlikely you'll have next door neighbor interested in LF reception ... it hasn't been a much of a problem.

Jay W1VD




----- Original Message ----- From: "DK7FC" <selberdenken@posteo.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, December 10, 2018 11:08 AM
Subject: Re: LF: LF and VLF EbNaut

Hi Paul,

Am 09.12.2018 20:02, schrieb N1BUG:

The first thing people want

to know is what equipment is required for LF EbNaut and how much is

this going to cost? But answers are hard to come by. I could never

get an answer as to whether my HP 3325B with high stability option

was good enough.

The problem is also on the other side. I don't know what a HP3325B is, or, at least, i don't know the technical details since i don't own one. So i can give no advice how to use it for EbNaut transmitting

Also there are different methods and each radio amateur is convinced about his own design.

Some methods may be easier to realise but less precise and less flexible. So based on the skills and needs and parts available one will decide for a certain design.

Thus it is not so easy to write up 'the' way to go, there are many ways. For example, there could be a 'how to EbNaut' including Linux components like ebkey, which will be useless for someone who insists to avoid using Linux...

So if you're asking the group, then you will get different advice, from different designs. And this will be confusing! So concentrate on the basics and then choose your own design.

I suggest to start in steps, don't plan to build the perfect system until the season is over.

Basically all you need is an absolutely stable signal generator and a tool for inverting the phase and managing the timing. This can be done with Windows and Linux.

I think you are one of those who avoid using Linux. So then, you need SpecLab to generate the PSK.

But step 1 is the stable signal.

One method is to use an up-converter and SpecLab to generate EbNaut. SpecLab can generate a tone on e.g. 12500 Hz which is then mixed with 125 kHz, so there is an output at 137.5 kHz. This is how i do it here.

I can tell you about other methods but this may lead to confusion already.

Maybe there is one step before step 1, call it step 0: You need to decide, "YES i will now start to transmit EbNaut and i will buy to necessary components, learn what is necessary to understand, knowing it means effort!"

What kind of signal generator do you use now?

When I asked about amplifiers for EbNaut I was told

linear is a must

Do you remember who said that?

but now I find people are doing it with nonlinear

amplifiers

Yes, a linear amplifier is not needed. It is BPSK, the output power is always at 100%, which is good :-)

73, Stefan