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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.
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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