LF: Re: DBF39 in VK

Frank Gentges gentges@itd.nrl.navy.mil
Tue, 26 Jan 1999 03:47:39 +0000 (GMT)

The group,
This fellow is on the same line of reasoning I was on when I wrote the 
paper on signal strength estimation.  I want to refine my thoughts into 
an equation we can work with.  Anyone have any thoughts on how to plug in 
some of the other numbers we need?   If this fellow is anywhere near 
right then we need to narrow up our detection bandwidths a lot and 
integrate the signals for some time.  I have looked at the VK web page 
and he is doing some interesting work.  One thing that bothers me is the 
use of a one bit A/D converter.  While it may pull a single sine wave out 
of many db of noise, my experience is that if any other sine wave is 
within the band it will capture the system much like an FM detector and 
any weaker sine waves may be lost.  With 16 bit sound cards on our PCs 
this should not be necessary.  More stability in the A/D clocking may be 
needed and receiver stability may be a challenge.  For the short term 
this may be the best approach to getting the dbs needed to detect the 
Euro stations.


On Mon, 25 Jan 1999, Andre' Kesteloot wrote:

> AMRAD Gang,
> let us think about the VK calculatiosn re-our own operations
> Andre'
> Steve Olney wrote:
> > > Hello,
> > > Steve's graph of the station on 138.830 is very interesting. If a signal
> > > such as this 60 kW (some say 100 kW) can be pulled out of the noise by
> > > integrating the signal over 30 minutes, maybe we need to ask Europes
> > > strongest station (G3LDO?) to use vscw (=very slow cw) and use dot length
> > > of hours or even a dot length on one day .... just a thought ...
> >
> > I have been thinking about this for a while now.  Assuming 100kW and an
> > EIRP of say 80kW for DBF39 and best EIRPs of about 1W for an amateur setup,
> > we are almost 50dB down.  The display S/N of DBF39 is about +10 S/N for a
> > 30 minute record.  I need at least a +3dB display S/N to make a positive
> > identification.  That leaves us with a deficit of 43dB.  If you look at the
> > new images I have put up on my Web Page you can see that the DBF39 is
> > spread over about 80 FFT bins.  If you could contain the amateur signal in
> > one FFT bin (0.009ppm - need to be locked to one of the time and frequency
> > station signals at both ends) you would get a 19dB improvement.  That
> > leaves us with a 24dB deficit.  If we integrate over about 2 hours (the
> > current dark path window to VK from UK) we gain another 6dB.  Still 18dB
> > down. Doesn't look promising.
> >
> > On a more optimistic note the records I have taken are only a small sample
> > (2 runs) and it is possible that some form of enhancement may exist (SIDs)
> > which could get us over the line.  Also the records here are taken over the
> > western path from here which is mostly over land.  At other times of the
> > year a dark path may be possible to the east of the Pacific/Atlantic which
> > should be better.  ZL is better placed now as they have a dark path over
> > Pacific/Atlantic.
> >
> > The new images (DBF39? and DCF49?) are found by taking the "Other LF signal
> > sources" link from
> >
> > http://www.zeta.org.au/~ollaneg/lowfer.htm
> >
> > 73s Steve Olney (VK2ZTO)
> > ========================================
> > email:  ollaneg@zeta.org.au
> > Web Page:  http://www.zeta.org.au/~ollaneg
> > LowFer: http://www.zeta.org.au/~ollaneg/lowfer.htm
> > LF Receiving - FRG-100, 8-turn 10sqm Loop
> > or Ferrite Loop + K0LR Preamp
> > ========================================