Hi Paul, Markus and all,
in this weekend i have made a simple modification at my LF TX to improve
frequency stability.
I have phase-locked the 10 MHz OCXO of the exciter with the 10 kHz
signal coming from the GPS.
Thanks to Markus DF6NM, signal was analyzed yesterday and today during
some op-32 and Ebnaut transmissions. Modification seems working since
Markus was able to decode me without changing frequency offsets.
I'm making now some EbNaut transmissions on 137502.24 Hz every hour
(started at 10.00 UT). Message is composed by 25 characters at 1 s per
symbol. Coding selected is 8K19A. Carrier starts 5 minutes before EbNaut
sequence and ends at XX.30.
Power output is 100 W and antenna is inverted-L 8 meters high.
Signal should be visibile at DF6NM OPDS grabber
https://dl.dropboxusercontent.com/u/26404526/opds.htm in the middle of
the its right window.
I will stop the session tomorrow at 08.00 UT
So Paul, hoping that your receiver is completed and your antenna is
already plugged in, you can try to receive my signal. However let me know
if some EbNaut-tx parameters need to be changed and, of course, you
can ask for a transmission at any time.
Thanks for your EbNaut great work.
73, Domenico / iz7slz
On 10/18/2015 9:18 PM, Paul Nicholson wrote:
Spent some time today cobbling together a receiver for
137 kHz. System noise measures about 4nV/m equivalent
field strength in 1Hz with a BF245B front end but I've
not yet attached it to an antenna - that's usually when
the trouble starts.
The mono audio input of the BT878 video card timestamps
fairly well while sampling at 448k samples/second. It's
a bit noisy: 3.5 uV RMS in 1Hz at the line input, which
means I needed to build in quite a bit of rx gain to
overcome the card floor.
Because it's a mono audio input I have to mix the GPS PPS
and the LF, then separate them again in software.
Hopefully soon then, some phase measurements at LF.
--
Paul Nicholson
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