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Re: LF: DK7FC VLF carrier

To: [email protected]
Subject: Re: LF: DK7FC VLF carrier
From: "Mike Dennison" <[email protected]>
Date: Fri, 29 Sep 2017 13:58:43 +0100
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In-reply-to: <[email protected]>
References: <[email protected]>, <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Stefan, thanks for the comments. My locator is IO92VT, Welwyn Garden 
City, just north of London.

I was using an "equivalent noise bandwidth" of 44uHz which meant 
around 9 hours per pixel. If you look at the right hand side of the 
picture the difference between the long term average on your 
frequency (red line) and the average noise seems to be about 5dB 
(10dB per div). 

I have added quite a bit of hard limiting in SpecLab's Blackbox 1 and 
this tends to smooth out the nighttime noise peak.  

Also, I have increased the "internal average" in the FFT menu to '2', 
which reduces the displayed noise but makes the start/stop edges 
rather fuzzy.

I will try two spectrograms later as you advise.

A question about SpecLab: When setting the bandwidth in the FFT menu, 
what is the difference between the "Decimate.." and the "FFT input 
size" settings. They both seem to produce the same result, eg 
Decimate at 2048 and FFT at 262144 gives a bin width of 44uHz, and 
Decimate 4096 and FFT 131072 gives the same. Why should I set one 
high and the other low?

Thanks again for the carrier.
Mike, G3XDV

> Hello Mike,
> This is a very good result!
> But it is a bit difficult to read the SNR. The relatively high SNR
> would allow you to run a faster spectrogram. What is the current one,
> maybe 30 uHz (value of "width of one FFT bin")?. If so, you could try
> about 60 uHz and a 2 times faster scroll rate. This will lower the SNR
> by 3 dB but you can see more pixels and see how the signal level fades
> during the night time. You can also run 2 SpecLab instances
> simultaneously and can decide later which of the two spectrograms are
> more informative... It appears to me that the QRN is lower during the
> last few days, which also helps us of course.
> What was your locator? Something in IO92, right?
> There have been a few more requests for another carrier this night, so
> i will just continue to transmit that night. Just follow the
> grabber... Due to the lower QRN, Paul may decode the 100 character
> message after 3 (or even 2) days already, so i would consider to run a
> 24 hours or 36 hours carrier before i actually move to 6.47 kHz with
> the new coil...
> 73, Stefan
> Am 29.09.2017 13:53, schrieb Mike Dennison:
> > Thanks to Stefan for transmitting a carrier overnight. This is very
> > useful for those of us who are not quite ready to decode EbNaut
> > transmissions but want to optimise our VLF reception.
> >
> > My screenshot is attached.
> >
> > Mike, G3XDV
> > ==========
> >    
> >
> >
> > The following section of this message contains a file attachment
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> >
> >     ---- File information -----------
> >       File:  DK7FC_VLF_28-29Sep2017.jpg
> >       Date:  29 Sep 2017, 12:44
> >       Size:  36265 bytes.
> >       Type:  JPEG-image
> >    
> ---
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