To (temporarily) conclude discussion of "The art of
measuring Fs and EMRP of an LF/MF transmitter" from
my part, I (exceptionally) ATTACH short text in hope
that file is small enough and everybody can open
and read ASCII text. From text it should be clear
why this subject is up-to-date for me personally.
Yleisradio (Digita Oy) has decided to terminate all
continuous LF/MF field strength measurements.
Having been involved in these myself for 40 years,
my duty in the future will be to document what I can.
Some field measurements, no doubt, will be done also.
Everyone interested to see pictures (eg of mentioned
Tallinn "super beacon") or anything else, let me know.
73 de Vaino, OH2LX
THE ART OF MEASURING FIELD STRENGTH OF AN LF/MF STATION
YLE activity started in 1948 at Helsinki-Laajasalo and
continuous LF/MF measurements by Yleisradio Oy and newly
established Digita will be terminated as of 31st Dec 1999.
First LF/MF Fs measurements and calculations of effective
electrical ground conductivity were made during years 1930-
1940 by prof V. Ylostalo of Helsinki Technical University.
The results have been confirmed in 1950-1999 measurements.
The Fs measurement system operated by YLE at Jokela, Finland:
- PC (+ man) controlled 24h Fs measurements with equipment
in use after 1988 in electrically controlled environment:
- R&S ESH3 scanning 30 LF/MF/HF frequencies, of which
25 served also as a ground wave research check, with
frequencies between 85.27 (local Decca Master) to
558 kHz and ground distancies between 12-580 kilometres.
222 measurements per hour per frequency (which in about
11 years means 21 million data points per frequency).
The validity of ESH3 measurements could be checked with
R&S HFH1 (2x) and ESH2 with loop and rod antennas.
During field measurements by car and/or airplane, all
possible means were used to cross check everything.
Flight measurements consist of some 500 flight hours of
radial attenuation measurements, and occasional vertical
pattern measurements eg of Lahti 254/252 & Turku 963 kHz.
Field measurements include eg some 60 Finnish airfields.
THE ART OF ESTIMATING EMRP FIGURES FOR AN LF/MF STATION
These calculations are currently based on flight attenuation
measurements of a number of stations. Best available programs
developed by EBU, CCIR, OIRT and other Study Groups have been
applied in the calculations of EMRP from flight (and other)
measurements available for these purposes. Some institutes
currently have their own ground conductivity data banks.
While EMRP calculations based on recent flight measurements
are rather straightforward they appear to be hampered with
time by changes both in radiation efficiency of a transmitting
station and variation of so called "effective electrical path
conductivity" (a conductivity actually "seen" by radio wave).
This is what is shortly called "effective ground conductivity".
All accurately enough calibrated long time ground wave measur-
ements shown clear variation as a function of air temperature.
In Southern Finland, Winter time GW values are roughly 3-7 dB
higher compared with the Summer time values. This phenomena was
documented by a number of authors already in 1940's and 1950's.
This leads to a difficulty to decide which EMRP to advertise.
The Civil Aviation Authority of Finland currently uses Nautel
transmitters for NDB and Locator beacons, the tx power varying
between 100 and 500 W. Most Finnish and Swedish DGPS beacons
also use 100 W or in some cases 50 W or 200 W transmitters.
Most new generation beacon transmitters are in itself rather
stable. CAA beacon antennas (h=14 or 11 m) don't look or behave
very nicely compared with old generation, higher steel tube
antennas, with some installations now looking less professional.
One out of five Loc beacons at Helsinki-Vantaa has been almost
excessively sensitive to all changes in local weather. Sometimes,
to compensate, the output tap of ATU must be manually readjusted.
I discovered a report by FOA (Swedish Military Research) dated
in May 1970. The effective ground conductivity of Swedish soil
was flight measured in 1967-1968 using existing Decca stations.
They concluded that "sigma" values for typical Swedish soil are:
For 70 kHz = 0.2 to 0.3 mS/m and for 128 kHz = 0.3 to 0.5 mS/m.
NOTE: The average soil in Finland is not much different from
that in Sweden. Really large scale flight measurements in
1974-1977 in Finland were made using existing NDB/Locator
beacons and existing and temporary LF/MF BC-stations.
All effective ground conductivity values were reducted to
700 kHz, to be presented at European LF/MF BC Conference.
V.K.Lehtoranta, OH2LX, Jokela 27.10.1999
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V.K.Lehtoranta, OH2LX, POBox 50, FIN-05401 Jokela, Finland
------ Tel: +358-9-4173965 ---- Fax: +358-9-4173961 ------
E-mail: [email protected] - alias: [email protected] & [email protected]
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