Hi Tony,
There is a box/field named "Max deviation from initial sample rate".
Currently there is a value of 20 ppm i guess. Just set it to 50, press
Enter or Apply, wait until the field becomes green ("PPS peaks OK"),
then press the ">>" button and Apply again. Wait until the field
becomes green again. The values should then be very small, 0.0xy ppm.
Reduce the value from 50 ppm to 10 ppm then and press apply.
Everything should be fine then.
Are you getting a spectrogram and text files to the stated folder? You
need to wait an hour or so for that!
73, Stefan
Am 30.10.2016 13:46, schrieb Tony Baldwin:
Hi Stefan
Thanks for part 2
Today I found the time to try to set SpecLab up and have immediately
run into a problem.
1 pps fed into right channel and level suitably reduced, and onboard
sound card set to 48000
I get an error in the component box saying "sample rate too far off".
It appears to be off by 32 - 38 ppm and the SR is 48001.5 to .7
Is that adjustable or does it mean the sound card useless? (the "sound
card" is on the mother board)
73, Tony, EI8JK
On 24/10/2016 14:54, DK7FC wrote:
Hi Tony,
OK so if your RX and PC time is stable, we can give it a try.
-You need a stereo input soundcard and feed the PPS signal to the right
channel. Just run it at 48 kS/s. The PPS signal must be DC decoupled
and the level must be limited to 80% of the ADC range, simply use 100nF
and a resistive divider. The values will depend on your GPS module and
its output level.
-Download the latest version of SpecLab and install it to the
recommended folder.
-Turn the RX to 136.00000 kHz USB and use a 2.5 kHz wide SSB filter.
Connect the RX to the left channel of the soundcard input.
-Download the usr file in this mail and open it into SpecLab (File
-> Load settings from...)
-Click on Components -> Show Components. A box opens. In the top
left corner, click on "SR cal". Another box opens. The Status must be
green, showing pps peaks OK. If the level is to high, click on "scope"
and see the peak form. Then you need to adjust the divider of your GPS
module to reduce or increase the PPS level. The box must be green for
most of the time in the end. Click to scope again, there is a pulse
counter PC and an error counter EC. The error should be lower than 2 %
or so, for example PC=1000 EC=16. Just let it run a few hours and see
if the tracking is stable.
If you have problems in this step, tell us what the problem is.
-Wait a few hours and check if text files appear at C:\Spectrum\data
After the first 40 minutes, a file should appear each 10 minutes.
-Ask someone to transmit a short EbNaut message at 1s symbols and make
sure to record on this time.
So far. Then we can continue with part 3 :-)
73, Stefan
Am 23.10.2016 19:09, schrieb Tony Baldwin:
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
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