This is a very interesting discussion!
This is the kind of basic information I wanted: what performance
specification should we meet for good results. When I know that, I
can begin to look at options and make sensible choices. When one
does not not know what performance standard he is trying to meet, it
is difficult...
Until now as far as I knew any useful GPSDO cost at least 150 USD.
I thought the NEO-7M / NEO-M8N devices were useful mostly as a 1 PPS
source but not good enough as an oscillator / RF frequency source. I
was looking at some data sheets, app notes and forum on the Ublox
web site. They seem to mention some concerns about jitter and phase
noise which I didn't fully understand with regard to our purposes.
Can we have some more discussion around using the NEO-7M / NEO-M8N
devices in such applications please? Is there nothing to worry about?
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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