Hi LF & VLF,
Yes, Stefan. I'm using both the NEO-7M and the NEO-M8N. The accuracy is obviously guaranteed by the GPS signal. Programming the TP5 at low frequencies (< 1MHz), there are no problems, I only recommend to put an adequate low-pass filter on the TP out. With higher frequency (especially >5 MHz, max. 10 MHz), it gets severely affected by glitches making it compusory to use an external LO locked to TP output with a PLL circuitry. With U-center software in config view, NAV5 settings, I also recommend to set "Stationary" dynamic model and Min. SV elevation to 10 deg. to achieve better performance. Anyway, I think the better Ublox module for this LO utilization is the little more expensive NEO-M8T (already mentioned by Paul Nicholson) which has two indipendent programmable TP outputs, it is Galileo ready and its internal reference TCXO circuitry is much better than normal NEO-6/7 series. It permits to discipline a receiver and, at the same time, the PC audio with a 1PPS signal.
All the best
73 de Riccardo IW4DXW
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
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