Hi Paul,

Am 12.12.2018 13:31, schrieb N1BUG:

They seem to mention some concerns about jitter and phase
noise which I didn't fully understand with regard to our purposes.
  

Me too. It never appeared to be relevant for me. It only seems to be a matter for the perfectionists. Also that discussion about short term stability and long term stability. I never cared about that and treated these NEO modules as the perfect signal source.
If i can transmit on VLF with a signal based on such a module, i can integrate 1 day into 1 pixel, i.e. 11.574 uHz FFT bin width. If the results are fine, why should i spend a thought about stability anyway? Even stacking of several days is no problem.

Once again that image:


...transmitted from my INV-L antenna, received on the tree, both systems using a NEO-6M as the reference and SpecLab to receive and transmit. 4.1 uHz FFT bin width. The peak is EXACT on the frequency and i find it quite sharp, considering that the tree is moving a bit in the wind and there are temperature changes and day/night differences...
So, why to spend more thoughts about accuracy??????

Can we have some more discussion around using the NEO-7M / NEO-M8N
devices in such applications please? Is there nothing to worry about?
  

Maybe IW4DXW can comment. Also some photos would be interesting.
In a few weeks i can contribute to this as well. And i'll try to build a transmitter in combination with a Raspi and vlfrx-tools.

73, Stefan

I had some ideas in mind if the unit is suitable:

LO for a 136 kHz > audio down-converter (Rx)
LO for a audio > 136 kHz up-converter (Tx)
Replacement for xtal LO in my LF SDR receiver (400 kHz)
Replacement for xtal LO in my MF SDR receiver (1.8 MHz)
Maybe a few others...

73,
Paul




On 12/11/18 4:15 AM, DK7FC wrote:
  

...indeed. And this GPS derived oscillator can be a NEO-7M, which costs 
about 10 EUR, or 10 $ as i can see at amazon.com.

73, Stefan

Am 11.12.2018 00:57, schrieb Markus Vester:
    

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 <[email protected]>
An: rsgb_lf_group <[email protected]>
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, <[email protected] 
<mailto:[email protected]>> <[email protected] 
<mailto:[email protected]>> 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" <[email protected] 
<mailto:[email protected]>>
To: <[email protected] <mailto:[email protected]>>
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