Markus,
Thanks for the tip about using a double balanced mixer (DBM) for generating
the 180 degree phase shift. It works perfectly and simplified my hardware
arrangement with the HP3325A! I did insert a 330 ohm resistor in series
with the RS-232 RTS line to limit current through the DBM. FYI, I do use a
10 MHz GPS-based input to my HP-3325A so frequency accuracy and stability
concerns are minimum.
Tips always welcome & 73,
Rob - K3RWR
Sent: Monday, December 10, 2018 11:57 PM
Subject: Re: LF: LF and VLF EbNaut
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
AMSubject: 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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