Re: LF: Idiot's guide to receiving Ebnaut? - Tutorial part2

[Andy Talbot <andy.g4jnt@gmail.com>]

Has anyone tried locking an external USB soundcard to GPS?  Chips such as the PCM290x family use their own 12MHz crystal, and it's relatively straightforward to provide 12MHz locked to some master reference like GPS to drive this.

So, in theory, the 48000 and lower sampling rates will then be spot-on.  However, I fear there may be slippages in the USB interface as the 12MHz external clock, and the USB's 6MHz clock slip past each other, resulting is lost packets and corrupted data samples

I do use a homebrew PCM2900 soundcard for data comms work, but never tried locking it.  Instead, for LF work I instead use the external digitiser, sending data to the PC on a RS422 interface; as described in the link sent earlier. The PIC digitiser, working on a 1kHz tone, can be used with any suitable receiver

Andy  G4JNT

On 23 October 2016 at 18:09, Tony Baldwin <ei8jk@topmail.ie> wrote:

Hi Stefan
 
My receiver is an Elad FDM-DUO SDR with a 10 MHz GPS input.
Unfortunately SpecLab doesn't have that radio for an SDR input, so I have to use the sound input via USB.
I could send the 1 PPS to my computer via RS 232 as well if that helps.

73, Tony, EI8JK.

On 23/10/2016 17:51, DK7FC wrote:

Hi all,

I started to write the second part of this tutorial but when finished i was not happy with the result.

The first thing one can say is that you will need a very frequency stable receiver. There is no chance without an external reference signal. For generating wav files using SpecLab you will also have to use a ref signal to compensate the drift of your soundcard. Some people have already prepared things in the past. You can use a 1 PPS signal for soundcard drift compensation or a down divided 10 MHz GPS reference or a stereo soundcard receiving VLF MSK signals on the other channel to compensate the drift.
Also the SpecLab configuration depends on your receiver type.
Now i could simply make some assumptions what your equipment may be but this may be not a good way.
So now i think it's better that we start with one example, one (or more) of the stations who are interested in EbNaut decodes on LF should describe the available system components. Then we can work it out what must be done.
We will need to have a stable RX frequency and a drift compensated soundcard frequency in the end.

So who of those who are interested wants to start?

73, Stefan