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To All from PA0SE
I only could monitor transmissions from the
ex-Decca station today, Sunday April 16.
The result is:
Time (UTC) Call Freq
ERP Iant S-report Fieldstrength
1000
G3WSC/P 136kHz 50W 9A S9 +
20dB 171 µV/m
1446 G3GRO/P 73kHz
? 9A S9 +
7dB 70 µV/m
The distance between Puckeridge and PA0SE is 317km, for
the larger part over sea.
The CCIR curves show that for this distance at 136 kHz
attenuation over sea water and "land" hardly differs from a path over perfect
ground. Assuming perfect ground we can apply the simple rule that 1kW
transmitted from a small aerial produces a field strength of 300 mV/m at 1 km
distance and this decreases in a linear way with distance. Working backwards
from the field strength measured we find at Puckeridge 45W was fed to the
aerial on 136kHz and 7.5W on 73kHz.
This is EIRP and not ERP of course.
In order to enable the station receiver to be
used as FS meter I measured the FS of DCF139 (138.83kHz) and DCF77
(77.5kHz) at two locations in open field, using a home made one turn
screened loop of 1 m^2 area and a Wandel & Goltermann SPM-12 selective level
meter, fed from the car battery.
I could have saved myself the trouble because the values
measured at the two locations and the ones in my shack were exactly the
same:
DCF139: E = 1.93 mV/m
DCF77: E = 2.85 mV/m
It shows that the magnetic component of the field is not
noticeable influenced by wiring, central heating system etc. in the
house.
When using my home made portable FS meter, described on
G3YXM's website, I had noticed that moving around outside over a small
distance sometimes made considerable difference in FS measured. I attribute this
to underground cables, pipelines etc. These extend over a great distance, pick
up the signal as a long aerial and re-radiate it, interfering with the primary
field. (On LF the field penetrates over tens of metres into the ground). The
dimensions of objects inside the house apparantly are too small to show
this effect to a measurable extent. (Inside an appartment block with concrete
walls it may be different.)
When I measured the field of DCF139 and DCF77 I selected
locations where no such visible and invisible field-disturbing objects
were present.
I sincerely thank all those who took part in organising
and performing this interesting experiment and in particular Walter
Blanchard who was instrumental in making it possible.
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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