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LF: Signals measured

To: "LF-Group" <[email protected]>
Subject: LF: Signals measured
From: "Dick Rollema" <[email protected]>
Date: Mon, 26 Jul 1999 16:50:11 +0200
Cc: "Ger van Went, PA0GER" <[email protected]>, "Hans Peltzer, PA0HRP" <[email protected]>, "Klaas Spaargaren, PA0KSB" <[email protected]>, "Jan Hekkert, PA3HCD" <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
To All from PA0SE
 
For the second time I have been measuring signals received here.
 
The substitution method was used again: the output from the receiver is fed to a 35 Hz wide audio bandpass filter and then to headphones and an oscilloscope. The gain of the receiver is adjusted for a suitable deflection on the scope. Next a signal generator is substituted for the aerial and its output adjusted for the same deflection on the scope. The strength of the signal is then read from the attenuator and level meter of the sig gen. (HP 606B).
 
Date   Time   Call            Input receiver   Field strength    S-report
            UTC                            dBm             dB(uV)/m
 
23/7     1725    DCF39               -33                    65                 S 9+40 dB
 
23/7     1846    G4GVC              -84                    13.9              S 7
 
 
24/7      0225    DCF39               -37                    61                 S 9+36 dB (weaker than at daytime!)
 
24/7      0700    DCF39               -32                    66                 S 9 + 41 dB
 
24/7      0710    G4GVC              -83                    16                 S 7/8
 
24/7      0729    GM/G3YXM/P     -91                      6.8              S 6
 
24/7      1029     PA0VBR            -92                      5.9              S 6  (new station, his first QSO)
 
 
25/7       0703    DCF39               -32                     66                S 9 + 40 dB
 
25/7       0715    GM/G3YXM/P     -93                       4.9             S 5/6
 
25/7       0723    DL3FDO             -96                       1.2             S 5
 
25/7       0800    G4GVC               -84                     14                S 7
 
25/7       0845    G3KEV               -80                      18                S 8 
 
25/7       0903    OZ1KMR             -80                      18                S 8
 
25/7       0907    OZ5N                  -88                      10                S 6/7
 
25/7       0915    ON7YD                -83                      15                S 7/8
 
A pity I heard no more stations.
 
For the S-point calculation I used the IARU recommendation: S 9 = -73 dBm; 1 S-point = 6 dB
 
For the field strength I used the earlier found relation e/E = 2.83 in which e = voltage at the aerial terminal of the receiver in microvolt; E = field strength in V/m.
 
The accuracy gets worse as the signal received is nearer to the noise level. The noise also corrupts the picture on the scope screen and it becomes increasingly difficult to read the amplitude of the signal in a mixture of signal and noise.
 
The minimum discernible signal by ear and scope at my location is about -97 dBm (S 5 in 35 Hz bandwidth).
It means that if I hear a signal it must be at least S 5. It confirms my earlier finding that an S-report by ear on a weak signal tends to be pessimistic. For relatively strong signals reports by ear agree pretty well with measured ones.
 
In a QSO with Dave, GM/G3YXM/P, I gave him S5 by ear and measured S 6.
Andries, PA0VBR got S 4 by ear and I measured S 6.  
I must try to remember that for future QSO's.
 
Now on a entirely different subject.
 
Alan Melia in his e-mail of 18 July, 23.12 hrs, mentioned F5MLP as a station having difficulty in getting started on LF.
I think beginners like F5MLP would be well advised to buy the LF Experimenter's Source Book by Peter Dodd, G3LDO at the RSGB Shop (hope he can read English). It gives precisely the sort of information a beginner requires.
 
In my opinion a real amateur who likes to experiment should invest in Test Gear, Literature and a Personal Computer with suitable software.
 
By chance I came across a very good article: "PROPAGATION OF LONG RADIO WAVES" by J.A. Adcock, VK3ACA. It appeared in the Australian magazine Amateur Radio in 4 parts, June to September 1991.
The article provides a thorough treatment of the subject, starting off  with basic concepts like refraction, reflection and diffraction.
It answered many questions I had about propagation at LF.
 
I found the article at and downloaded it from our VERON website: http://www.veron.nl.
Next click on HAMRADIO and LF-BAND; you find the article under the heading ''Engelstalig". 
 
73, Dick, PA0SE
 
JO22GD
D.W. Rollema
V.d. Marckstraat 5
2352 RA Leiderdorp
The Netherlands
Tel. +31 71 589 27 34
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