Re: LF: EbNaut transmission test in LF

[DK7FC <selberdenken@posteo.de>]

Hi Luis,

Are you sure that the phase shift is 180 deg? At 180 deg there should be no peak in the red spectrum (Markus' tool show_rawsyms3b). Are you transmitting the carrier permanently and just do the keying for those 9.3 minutes? Then maybe there is just a timing problem.

Do you generate the RS232 keying with SpecLab? If so, do you consider SpecLab's internal time offset of 0.3 seconds + 4/samplerate? Here it is 0.812 seconds, which is a very significant part of the symbol length and thus most important to consider. However i'm not sure if this also applies when using the serial interface...

Can you tell me the message? It is easier to find the reason when already knowing the message.

73, Stefan

Am 07.09.2018 11:28, schrieb VIGILANT Luis Fernández:

Hi LF EbNauters

 

I have been building a disciplined Rx for LF, based in a GPS LO at 120KHz and a NE602 downconverter to 17KHz

Then feeding the signal to the soundcard, also disciplined with 1pps from the same GPS

 

At Tx side a GPS LO at 1374850 Hz divided by 10 provides 0.1Hz steps at LF. Then an XOR gate is used for

EbNaut modulation from the DTR of  a COM port under Windows. The PA is just a mosfet driver (mic4452 AT 12v)

Just about 100mW to antenna but good enough to get a 20dB S/N in my Rx 7Km away

 

Stability looks pretty good and also phase modulation as seen in SL spectrogram. Also monitoring phase changes

with the SL plot display window. So, yesterday I tried an EbNaut transmission with the following setup

 

Coding: 8K19A

CRC 16

Symbol period: 1s

Characters: 6          Transmission time: 9.3 minutes

Transmitting at minute 00 and 30 every hour

 

I got the FFT files from SL and converted them to WAV files. The configuration file (SR) included the corrected sample rate

of the soundcard as well as decimation , FFT length and center frequency

 

Attached is a WAV file starting at 16:22 which should contain the transmission started at 16:30 untill about 16:40

 

The rawsym graphic shows a clear peak centered in frequency, but I haven’t been able to get a decode other than “******”

At least the decoder is detecting the carrier but may be there is no proper phase modulation or probably other failures

What I’m doing wrong ? Can anybody decode the message from the file ?

BTW, I have used a list length of 47274 and also 141823, but nill L

 

73 de Luis

EA5DOM