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From: "Talbot Andrew" <ACTALBOT@dera.gov.uk>
To: rsgb_lf_group@blacksheep.org
Subject: LF: Larry's tests
Date: Thu, 18 Jan 2001 10:13:47 -0000
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> -----Original Message-----
> From: Rik Strobbe [mailto:rik.strobbe@fys.kuleuven.ac.be]
> Had a look for Larry's dashes over the last nights, but no positive
> bandwidths (0.05Hz and less). I can see the dashed line on 
> 137792 (as seen
> by DF6NM) very strong at night and weak at daytime, I don't 
> think that it
> is Larry.

It certainly isn't !     There are several signals a few Hz away from
137790Hz.  In a 2.5Hz bandwidth I clearly saw the following during
Tuesday nights test :

1)	Clean carrier at 137789.10  about 15 dB above noise in 0.015Hz
bandwidth
2)	Larry's signal at 137789.89, sometimes smeared out to as wide as
0.05 Hz  during the period around 2300z to  0300z - Due to Doppler
shifts and multipath ? - Then cleaned up and got stronger at 0500z.
This frequency measurement agrees with VE2IQ measuring locally.
3)	0200z to 0600z  A signal showing the same or even more smearing
at 137790.09 - a long distance transmission ?
4)	Fading or pulsed carrier that appeared at 0500z on 137790.35
5)	A pulsed carrier (variable switching periods of several minutes)
at 137790.36 (not the same as above !)
6)	A pulsed carrier (variable switching periods of several minutes)
at 137790.7

2) to 6) were all about 2 - 6dB above noise

Outside this bandwidth, but visible from Wednesday's monitoring, a
strong carrier at 137791.5 approx (didn't bother measuring it ) about 40
- 50dB above noise in 0.04Hz bandwidth. This is presumably what others
are seeing and mistaking for Larry !!  He is at least 30dB weaker that
this.

For last night's transmission I recorded raw data for a 6.25Hz bandwidth
at a sampling rate of 7.8Hz, any interesting results from post analysis
will follow........
For anyone else wanting to perform similar scientific measurements -
Spectran should just about cope, but you will need to calibrate your
soundcard sampling rate to at least 1ppm accuracy and receiver to
0.05ppm by receiving a standard frequency transmission such as MSF.  And
allow several hours for warm up drift.

It's rather satisfying that I can see something that looks like
ionospheric distortion on the signal.    One aim now will be to
post-process the raw data and filter out all the other lines as listed
above.   It would be interesting to make an "Ultra Dopplergram" to a
resolution of  0.001Hz or lower  over many hours to separate out the
separate signals that would make up the multipath.  
For some background reading on Dopplergram analysis of HF propagation
(Spectran does this beautifully) see G3PLX's article a couple of years
ago in RadCom

Andy  G4JNT


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