観測データ
HF Field Strength Data Measured at Syowa Station, Antarctica
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1. Introduction
The field strength of JJY (standard frequency radio waves) transmitted from Japan has been measured at Syowa Station, Antarctica, since 1958.
The receiver detects only the upper sideband component of the signal in order to avoid the co-channel interference.
This report summarizes the results of field strength measurements of JJY 8 MHz.
This HF field strength measurement was terminated due to the closure of JJY transmission.
2. Observers
| from January to December 1997 : | Jun OZEKI |
| from January to December 1998 : | Kenichiro KUSANO |
| from January to December 1999 : | Hiroshi NAKAMOTO |
| from January to December 2000 : | Astushi ABE |
| from January to December 2001 : | Hiroki KISHIDA |
Scaled by Miyako KODAIRA | |
3. Specifications of the Transmitter and Receiver
| Transmitting station | ||
| Call sign | : | JJY |
| Location | : | Sanwa, Sashima, Ibaraki Geographic latitude : 36ﾟ11'N, longitude: 139ﾟ51'E |
| Frequency | : | 8.0 and 10.0 MHz |
| Carrier power P0 | : | 2 kW |
| Modulation frequency | : | 1000 Hz |
| Degree of modulation M | : | 64 % |
| Antenna | : | Horizontal λ/2 dipole for 8.0 MHz Vertical λ/2 dipole for 10.0 MHz |
| Transmission time | : | 24 hours a day, except from the 35th to 39th minute every hour |
| Uncertainty of frequency and time intervals | : | ±1×10-11 |
| Receiving station | ||
| Location | : | Syowa Station, Antarctica Geographic latitude: 69ﾟ00'S, longitude: 39ﾟ35'E |
| Frequency | : | 8.001 MHz |
| Receiver bandwidth | : | 100 Hz |
| Antenna | : | Inverted L (height: 9.3 m, length: 2.2 m) |
| Distance between transmitter and receiver | ||
| Short path | : | 14130 km |
| Long path | : | 25870 km |
4. Derivation of the Skywave Field Strength
Calibration signals with 10 dB steps were inserted once a day from the standard signal generator to the input terminal of the receiver.
The input voltage of the receiver V (in dB relative to 1μV) is converted to field strength F (in dB relative to 1μV/m), adopting the substitution method.
A portable field strength meter was used simultaneously as a reference; it received the same signals.
This relation is written as follows :
Where K is the conversion factor which is a function of frequency, polarization and arrival angle of received waves, and antenna parameters.
The factor K was decided once or twice during the whole period of observation.
In routine observations, the median value of F received between 00 and 05 minutes every hour is scaled and then normalized with respect to the radiation power of 1 kW as follows :
Where Fm is the median equivalent incident field strength and P is equal to 10log 10log(P0M 2/4).
The conversion from Fm to the skywave field strength, which is indicated in the monthly table, is done following the procedures described in CCIR Report 253-5 (1990), on the assumption that the elevation angle of signals is 5o , and ground conductivity at the receiving site is very poor.
5. Monthly Tabulation Sheets
In the monthly tables, the hourly values for skywave field strength in dB (μV/m) are shown versus UT. The count, upper and lower deciles, upper and lower quartiles and the median values are also included in the tables.
The method for deciding these parameters is the same as the CCIR Report 253-5.
The following four letters are used in the tables for the receiving conditions :
Qualifying letters (preceding numerical values)
D: the numerical value is lower than a limit value
E: the numerical value is higher than a limit value,
Descriptive letters (following numerical values or alone)
C: no measurement was carried out or was possible because of technical trouble,
S: measurements influenced or impossible because of interference or atmospherics.
6. Diurnal Variations of the Field Strength
The diurnal variations of the monthly median values for the field strength are shown by solid lines in the attached figures, together with the decile range by vertical bars.
Arrows (↓) and (↑) on the vertical bars denote the meanings of E and D on the tables, respectively.
Acknowledgments
We would like to thank Dr. N. Wakai, for his suggestion about the derivation of the skywave field strength.
Reference
CCIR (1990): CCIR Report 253-5, Reports of the CCIR, Annex to Vol. 6, CCIR 17th Plenary Assembly, Dusseldorf, 1990.