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Date: Thu, 01 Oct 2015 16:29:52 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: Coherent BPSK on LF using EbNaut
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Status: O

Hi Domenico,

Thanks for your report.
I see you on my OPDS32 grabber, as you say.

2015-09-28 21:00:47 IZ7SLZ  1159km 137502.120Hz   1mHz -46.7dBOp  93% 17.9dB
2015-09-28 20:00:47 IZ7SLZ  1159km 137502.120Hz   2mHz -41.1dBOp  90% 20.4dB
2015-09-28 19:00:45 IZ7SLZ  1159km 137502.120Hz   5mHz -44.1dBOp  93% 18.8dB
2015-09-28 18:24:51 IZ7SLZ  1159km 137502.121Hz   2mHz -45.0dBOp  75% 15.2dB

Is 137502.120 Hz the frequency of your choice? If your TX and my RX is 
GPS locked (or tracked) then where does the 1 mHz offset come from? 
Maybe a phase variation due to changing propagation?
Which offset is acceptable to avoid SNR losses in EbNaut (at a symbol 
rate that allows a QSO (in one evening! ;-) )) ?

73, Stefan

PS: Unfortunately not QRV on LF at the moment. I need to find a new 
loading coil body because my glass coil fully broke during maintenance 
attempts. Now i need something to come out with a stronger signal 
because each modification on the system has to be an improvement, by 
definition. So maybe i can come closer to 1W ERP then...

Am 01.10.2015 01:53, schrieb IZ7SLZ:
> Hello LF and all,
>
> here's my "2 cents" about coherent-bpsk transmit point of view. I will 
> briefly describe the setup used by me during the tests and QSO with 
> DF6NM.
>
> I have employed an old analog SSB Exciter that has a resolution of 100 
> Hz. So, in order to set more exactly the frequency, exciter has been 
> programmed on dial 136.0 kHz and then modulated with a 1502.120Hz tone 
> to obtain the TX QRG used during QSO with Markus.
>
> The tone is generated by Spectrum Lab having sample rate calibrated 
> with  1_pps signal coming from a GPS (Rockwell Jupiter).
> Exciter is referenced to an 10 MHz OCXO (MTI-Milliren 230 series) 
> having a thermal stability of 2.5E-8.
> https://www.dropbox.com/s/wg0h78x31vdqr2i/OCXO.pdf?dl=0
> There is a plan to replace the OCXO with a 10 MHz GPS disciplinated 
> oscillator. This latter has been already ordered and it is on the way.
>
> Before entering in the SSB exciter, audio tone is passed through a 
> simple ring-modulator built with four diodes and two audio transformers.
> https://www.dropbox.com/s/gsf74bz8e1cqnmt/ring%20modulator.jpg?dl=0
> Ring modulator is driven by EbNaut-TX via RTS-DTR signals of the PC 
> com port. There is an option in EbNaut-TX to use RTS and DTR in 
> differential mode.
> 137 kHz output of the exciter, drives the 100 W PA.
>
> The use of SSB analog exciter, of course,  is not a good solution due 
> to the possible soundcard glitches. Markus suggests to generate the 
> carrier directly at RF i.e. using  an AD9850 DDS, and apply the DBM 
> modulation there.
> This solution will be also tested by me as soon as the GPS Oscillator 
> becomes available.
>
> Clock of EbNaut-TX Pc is corrected every minutes by a simple VB 
> program that reads the gps nmea,  extracts the time from GGA 
> "sentence" and updates the PC clock at 1_pps rising edge. In fact 
> 1_pps is also connected at CTS of the RS232 com port dedicated for the 
> GPS.
>
> Prior of any EbNaut sessions,  i made a check of the frequency by 
> sending some OP-32 sequences and looking my signal on the very precise 
> DF6NM and DK7FC OPDS grabbers (Thanks also to Stefan!). Markus has 
> kindly open a right window in his OPDS Spectrogram centered on 
> 157502.120 Hz.
> Then i just modify, in SL,  some mHz in the frequency of the tone 
> generator,  to compensate the error.
>
> In these days, observing DF6NM and DK7FC OPDS grabbers, i have noted 
> some stations with a very steady-frequency signal, i.e. G6AVK and 
> PA0OCD. I noted their signal during the night also on my receiver 
> setted in OPDS session mode. Unfortunatly their level is not enought 
> for an OPDS detection by me but i'm sure that is ok for a small EbNaut 
> message !
>
> So i want to invite this OM to try to bpsk-modulate their carrier 
> using EbNaut-TX.
>
> I'm at disposal for any sked.
> Most probably i will carry-out some EbNaut TX sessions during next 
> week-end. In case i will inform via this mail reflector some enought 
> time before.
>
> It's a great fun to play with these stuffs!
>
> 73 and GL all,
>
> Domenico (iz7slz)
>
>