...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
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]>
To: <[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
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