Very nice to see this working at LF with short symbols. The phase was stable enough for the 20 or so minutes of each transmission on this path of circa 1000km. S/N of IZ7SLZ at DF6NM suggests that a
The soundcard becomes a liability for coherent signalling at LF. The fiddly software is all concerned with coping with the wandering soundcard conversion rate. Yes, a small amount of hardware replace
Found myself ordering a Trimble 10MHz GPSDO the other day. I have a Thunderbolt but don't want to dedicate it to a receiver because it's handy in the lab. You might consider the packet format used by
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 -
The signal is much too strong to be a good test, you should still decode quite easily at DF6NM if you drop to 5W. I got the system noise down to 1.5nV/m per root Hz which is far lower than it needs t
I have an E-field rx running on the 137 kHz band, GPS locked. Here is the 'first light' spectrogram http://abelian.org/tmp/lf151023a.png which covers 137 kHz to 138.5 kHz. It's a bit shaky, everythin
From about 18:08:20 to 18:41 there was an immensely strong signal on 137508.82 Hz which looks like carrier but was very rough. Spectrum in 5mHz bins http://abelian.org/tmp/lf151023b.gif Looks like I
Thanks for the info. If that's an Opera signal then maybe my timing system isn't working so bad after all. I see. Hmm, a lot of energy in the carrier! Hopefully there will be some snippets of pure ca
Thanks, I was wondering about those. The tx is 155km from here. Those sidebands might turn out to be useful markers. Decoded easily: Eb/N0=7.5 ber=0.19 decode time 22 seconds Quite a strong signal, t
Having decoded the 20:00 UT 22 character message, I re-encoded it and used the symbols to phase modulate the received signal. The result is an unmodulated carrier which I can take measurements from.
Today I ended my brief foray into 137 kHz. The battery was going flat on the rx so I took it down. Reception at LF seems quite easy compared to VLF: much lower noise levels and much less interference
ebnaut-rx: 1/ Uses the integer sample rate given in the WAVEfmt block of the header; 2/ Expects an 'inf1' chunk following the 'fact' chunk; 3/ If the inf1 chunk contains a text string beginning sr=,
Feasible yes, but I wouldn't recommend it. I advise recording the signal first, then present the recording to the decoder. This, so you can repeatedly run the decoder with different frequency and ti
Somewhere I have a paper describing something like that. I recall an antenna at ground level or actually a little buried, and its effective height was related to the depth of the water table below t
We're well into the VLF season now so definitely time for some tinkering. What's your ERP Joe? If you can send GPS locked carrier, we can have a good look for it. That would be a start. -- Paul Nicho
PPS essential if you're using Spectrum Lab or vlfrx-tools. The GPS that I use these days is this one http://uk.mouser.com/ProductDetail/mikroElektronika/MIKROE-362/?qs=sGAEpiMZZMuNcqZxhMNT368vTF1vBnG
I tried the Fusion 878 card today. Unfortunately it's not a simple case of the wrong sample format. It does actually digitise the line in and the gain control, mixer input selection, and mic boost wo
Sorry, the previous message went to the LF group by mistake, I replied to the wrong thread. Messing about with a selection of BT878 video cards some of which have an audio line input which can sample
Thanks, that's a bug - it shouldn't need -S or -r when sending or receiving unmodulated symbols as text. Fixed now in version 0.2 http://abelian.org/ebnaut/ebnaut.c Now you can do, for example echo '
Even though I vaguely understand how it works I always find it fascinating to see. By flipping bits in test.txt you are adding binary noise, and the input of 0's and 1's to the decoder effectively fo
