This weekend (April 17/18) I measured the strength of signals in the 2 km band.
Reception is by an old LF-receiver type LWF45, covering 40 -160 kHz in two ranges, made by German firm Teletron. It is a hybrid design from the sixties with valves in the two RF stages and local oscillator and semiconductors in mixer, intermediate and audio frequency stages. The receiver has excellent front end selectivity: 4 tuned circuits ganged with the oscillator tuning. No need for external input filtering or attenuators here!
The output at 1000 Hz is fed to headphones via audio filters with 200 or 35 Hz bandwidth.
The voltage over the headphones is measured by a voltmeter and an oscilloscope. The receiver has manual gain control only, operating on the two EF39 variable mu pentode in the RF stages.
A signal to be measured is adjusted to a suitable level on meter or scope. Next a Hewlett Packard signal generator type 606B is substituted for the aerial, tuned to the same frequency and adjusted for the same reading on meter/scope. The signal strength is now indicated by the sig gen. For a further check the sig gen was connected to a very accurate selective level meter type PSM 5 made by Wandel und Goltermann. The sig gen level was found to be correct within 0.1 of a dB.
Local noise level was measured in 200 Hz bandwidth. In 35 Hz bandwidth the level is 8 dB lower, as expected. Conversion from dBm to S-points is according to the IARU Recommendation: S9=-73 dBm and 1 S-point=6 dB. Values rounded to nearest S-point.
I think figures measured are correct to about 1 dB. I found that on strong signals I would have given about the same S-report by ear as the one measured. For weak signals the report by ear would have been much lower, no doubt as the ear compares the signal to the noise level.
On an earlier occasion it was found that 33 dB of power is lost in the ohmic resistance of aerial, loading coil and earthing system. If this 33 dB is added to the dBm value measured the power collected by the aerial is known. For DCF39 this works out at 0 dBm, 1 milliwatt!!
Date
UTC
Station
Level dBm
S-report
16/4
1348
DCF39
-33
S9 + 40 dB
16/4
1352
Radio Greece on 135.8 kHz
-84
S7
16/4
2137
Local noise level
-75
S9
16/4
2137
DCF39
-41
S9 + 32 dB
17/4
0720
Radio Greece on 135.8 kHz
-82
S7
17/4
0721
DCF39
-34
S9 + 39 dB
17/4
0724
Local noise level
-100
S4
17/4
0743
Mystery stn on 137 kHz
-98
S5
17/4
0749
PA0KDM
-82
S6
17/4
0750
PA0LQ
-54
S9 + 20 dB
17/4
0756
ON7YD
-80
S8
17/4
0757
G4GVC
-84
S7
17/4
0803
G3BDQ
-88
S6
17/4
0839
Local noise level
-95
S5
17/4
0850
Radio Greece on 135.8 kHz
-80
S8
17/4
0904
G3KAU
-78
S8
17/4
0936
DCF39
-32
S9 + 41 dB
17/4
0944
DF2PY
-87
S7
17/4
1054
G3YXM
-82
S8
18/4
0721
DCF39
-33
S9 + 43 dB
18/4
0722
Radio Greece at 135.8 kHz
-79
S8
18/4
0723
Local noise level
-97
S5
18/4
0730
G3YXM
-81
S8
18/4
0731
PA0LQ
-55
S9 + 18 dB
18/4
0740
G4GVC
-85
S7
18/4
0744
G3XTZ
-80
S7
18/4
1019
G4GVC
-84
S7
18/4
1213
Radio Greece at 135.8 kHz
-82
S7
18/4
1215
DCF39
-33
S9 + 40 dB
By the way; in Dutch BTW stands for Belasting Toegevoegde Waarde=Value added Tax...
73, Dick, PA0SE
JO22GD
d.w.rollema@gironet.nl or pa0se@amsat.org