Date: Wed, 07 Sep 2011 11:26:30 -0400
To: rsgb_lf_group@blacksheep.org
From: Bill de Carle <ve2iq@magma.ca>
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Subject: Re: LF: beaconing to the west II ...and to the east, north and
    south...
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Hi Stefan:

I think I know how to configure clipping in SL (done it before) but 
by all means send me your usr - can only be helpful.  I've had good 
results with software clipping when I recorded the raw digitized data 
first then decided where/how clipping should occur after looking at 
it.  Too hard to predict optimum clipping settings for a long 
overnight run.  I didn't try recording last night: SL probably 
records incoming soundcard data before its internal sample rate 
correction is applied, so that would raise another issue.  I suppose 
I could add a sample rate correction step to the software I use for 
off-line processing, then we wouldn't need SL at all, hi!  Even 
uncorrected SC sample rate is likely stable enough for QRSS-60 stuff 
anyway, especially after a short warmup.  With the kind of band noise 
we had last night I don't think clipping would have been 
beneficial.  The Rx here is a TS-850 (master clock derived from GPS 
std), using CW mode 500-Hz IF filter with audio out at nominally 
800-Hz (actually, when the TS-850 is set to receive 136.172 Khz using 
1-Hz tuning steps an incoming carrier at that frequency will produce 
an audio output tone at 799.944 Hz).  The external GPS-monitored freq 
std runs 24/7.  Main advantage is a Rx that's instantly on-frequency 
and doesn't drift even right after turn-on.  Last night I had the Rx 
AGC enabled so lots of compression due to almost continuous static 
crashes.  I leave the RF gain at max when I go to bed because band 
noise often dies down at some point.  I was using a complex FFT with 
center frequency set to 800 Hz.  For some reason SL didn't like it 
when I tried to enter the more precise frequency and rounded it to 
nearest Hz.  I also have an SDR-IQ here which might be useful at 136 
Khz but didn't see your announcement in time.  The SDR-IQ isn't 
locked to an external reference so for long term carrier detection 
the TS-850 is preferable.  I'll run the grabber again tonite.  What 
time will you start Tx?
73,
Bill VE2IQ

At 09:51 AM 9/7/2011, you wrote:
>Hi Bill, again,
>
>Fine! So you will run the grabber tonite again? Looking forward to that!
>
>If the noise was "awful" (one can even see a broad band noise during 
>that time which must be local) and you use no noise reduction so 
>far, we will surely gain some dB soon :-)
>
>Yes, the trace was pretty exactly on the QRG and there were no other 
>traces like that on the whole spectrogram :-)
>
>About noise reduction: If you want, i can send you a usr file where 
>you can see how to arrange that if you don't know how. Where does 
>the AF comes out on your RX (e.g. 137 kHz = 1 kHz) ? What is the RX? 
>A HF TRX with a SSB filter?