Vol. Vol. 18 No. 97 four η al of the Radio Research Laboratories May 1971 Printed Printed in Tokyo, Japan pp. 183-190 UDC 621. 812. 391. 63. 029. 52 MEASUREMENT OF THE FIELD INTENSITY OF HF RADIO WAVES BY MEANS OF THE NARROW BAND RECEIVER By Noboru WAKAI, Shu FUJII and Yoshiyuki MIYAMOTO (Received (Received Aug. 28, 1970) ABSTRACT The narrow band receiver developed for receiving exclusively the JJY signals in in the presence of interference by other standard frequency waves with an identical carrier carrier frequency has been used since 1967 for the observation of HF radio wave absorption absorption in the nighttime on board the ship for the Japanese Antarctic Research Expedition Expedition （戸田町． This This paper describes the technical summary of the receiver, and presents the results results of measurement obtained by the receiver on the 10th (Nov., 1968 ～ Apr., 1969) 1969) JARE. Dependence Dependence of the ionospheric absorption in the nighttime on the solar activity was confirmed quantitatively by the same analysis as in the preceding paper. 1. 1. Introduction This paper forms substantially the second chapter of the preceding paper [Wakai et al., 1971] in which the results of observation of the nighttime ionospheric absorption absorption made on board ship for the Japanese Antarctic Research Expedition since 1958 1958 are presented. A portable HF 負eld intensity meter relying wholly on manual operation was in use use before 1966. In the second series of observation of the nighttime absorption after after 1967, automatic recording of the upper sideband of JJY signals was done by the the use of newly developed receivers capable of filtering out unwanted interference due to other standard frequency waves. This paper describes the technical summary of the receiver -as well as the results results of measurement obtained on the 10th (Nov., 1968 ～ Apr., 1969) JARE by the use use of the receiver, in order to confirm the dependence of the nighttime absorption on the solar activity by the same analysis as in the preceding paper. 2. 2. HF Narrow Band Receiver for Recording the Standard Frequency JJY The standard frequency waves in the HF range emitted on the same series of frequency frequency from various countries have several advantages in the practical usage. Nevertheless, Nevertheless, it brings trouble in receiving separately wanted signals, arising from 1邸 184 184 N. Wakai, S. Fujii and Y. Miyamoto the the mutual interference among the standard frequency waves with an identical carrier carrier frequency. These di 伍culuties were avoided by developing the narrow-band receiver receiver capable of picking up just the sideband of WWV and WWVH standard frequency frequency waves modulated by 440 Hz, for the purpose of the radio propagation warning service at Hiraiso Branch, Radio Research Laboratories [Isozaki et al., 1970]. 1970]. This type of receiver for recording automatically the field intensity of the upper sideband of JJY 2. 5 MHz waves (modulation frequency: 1000 Hz) was con- structed structed and installed on the ice-breaker "Fuji ” for the 9th JARE that left Tokyo in in November, 1967. The measurement of nighttime absorption with the changing distance distance of transmission was reinforced by adding year by year the receivers for JJY 5 MHz in 1968 (10th JARE) and then for JJY 10 MHz in 1969 (11th JARE~. Table 1 shows the summary of observation. The block diagram of receivers Table Table 1. Outline of measurement of the HF field intensity on board between between Tokyo and Antarctica Frequencies Frequencies Course v~~~ge Month, Year 豆罰 Observer J .A.R.E. (MHz) To Via 9th 9th Nov.-Dec., 1967 2.5 Tokyo Antarctica Australia 100 K. lsbizawa 10th 10th Nov., 1968-Jan., 1969 2.5, 5 Tokyo Antarctica Australia 110 Y. Ota 10th 10th Feb.-Apr., 1969 2.5, 5 Antarctica Tokyo Indian 108 K. lsbizawa Ocean Ocean R. Saruwatari 11th 11th Nov., 1969-Jan., 1970 5, 2. 5, 10 Tokyo Antarctica Australia 106 I. Shiro T. T. Sakamoto 11th 11th Feb.-May, 1970 2.5, 5, 10 Antarctica Tokyo Indian lOfi Y. Ota Ocean Ocean T. Hirasawa Fig. Fig. 1. Block diagram of a narrow band receiver for JJY 2. 5 and 5 MHz. HF Radio Wav e Int ensity by Narrow Band R e ceiver 185 fo r JJ Y 2. 5 and 5 MHz is shown in Fig . 1. Frequencies indi cate d outside bo xes in in the figure m ean th e operating frequenc i es in receiving 2. 5 (upper) and 5 (lower) MHz waves (a common operating frequency in the case of non-separation). The receiver is di stinctive in the fact that the output of I. F. A. (4 55 kHz ) is introduced introduced into C. M . F. I. F . A. ( Crystal Mechanical Filter I. F. A. ) w ith a bandwidt h of about ± 100 Hz in order to extract the respective upp er sideband com ponents (2. 501 and 5. 00 1 MHz ) of 2. 5 and 5 MHz waves . For this purpose, the the frequency stability of eac h l oca l osc illa tor (1st, 2nd and 3r d L. 0. ) is required to be mo re than about 1 ×10 -1. This req uir em ent was met by s uppl yi ng th 巴 output of external external osc illator s, sin ce the oscillators contained inside the co mmer cia l receiver proper (NRD -llE 〕 as enci r cled by a dashed line in Fig. 1 are unsatisfac tory in th 巴ir stability. Then the outp ut of C. M. F. I. F . A. is compressed logarithmically in C omp . wit h the dynamic ra nge of about 60 dB an d fina ll y recor ded on the strip chart recorder . The calibration of the receiver is mad 巴 by compari ng the vo ltag e from the the antenna w ith the signa l generator (S.G. ) in an ad 巴qua te int erv al of tim e. Th 巴 in st rum entation of th 巴 receiver for JJ Y 10 MHz is almost th e same as th at for 2. 5 or 5 MHz just mentioned, apart from the remova l of B. P. F . (14.5 ～ 15. 15. 5 MHz) and the 2nd L. 0. (17 .5 MHz ), and from the change of frequency of the the 1st L. 0. ( 13. 0 MHz ). '• 1 rt r r r r 10 同 iz OCT . 13, 1969 Fig. Fig. 2. E xa m p les of 1eco rd :obta in 巴d by the narrow ba 吋印ceivers (upp er, 10 M H z; lower , 5 MHz ). 1前 N. Wakai, S. Fujii and Y. Miyamoto Whip antennas 6m long are connected to receivers independently. In order to obtain obtain the absolute field intensity relative to 1 μV/m, measurement by means of the the portable field intensity meter as described in the previous paper [Wakai et al., 1971] 1971] was made once a day. Two examples of the record obtained by the narrow band receiver are shown in in Fig. 2. Letters ], W and B in the figure mean the signals from the transmit- ting ting stations JJY, WWV and BPV, respectively. Other standard fre~uencies such as as ZUO and LOL could also be received during the observational period, although they they are not recorded in the examples. It is necessary to know the schedule of emission emission and modulation on 1 kHz of the standard frequency waves from various countries, countries, in order to identify the transmitting station with the pattern of received signals signals on the record, unless otherwise the direct identification with the call sign. The modulation schedule pertaining directly to the measurement is illustrated in Fig. Fig. 3 [CCIR, 1966]. The upper record in Fig. 2 was obtained at Hiraiso Branch on October 13, 1969. 1969. On this record are seen intense signals with a drop in intensity due to the minute signal during O～ 10 minutes, 20 ～ 25 minutes, 30 seconds from 34 minutes, 40 ～ 50 minutes, and 30 seconds from 59 minutes. They are identified as JJY in reference reference to Fig. 3. Similarly, relatively weak signals received for 1 minute at 12, ト蜘『 ly modulatlon 。 倒閣ule 45 30 図凶：畑 ti 開国second 仰 l回困問 II sign Fig. Fig. 3. Emission and modulation schedules of various standard frequ ・ ency ency waves with a modulation frequency of 1 kHz. HF Radio Wave lntensi か by Nanow Band Receiver 187 17, 17, 32, 52 and 59 minutes are identified as WWV. The WWV signals to be record- ed ed at 7, 22 and 42 minutes could not be found owing to the masking by intense ]JY signals. BPV signals not registered formally by CCIR are emitted from Shanghai (China) or vicinity at three frequencies of 5, 10 and 15 MHz. The modulation schedule is also indicated in Fig. 3 as inferred from the survey by the Radio Regulatory Bereau in Japan. The BPV signals can be seen during 12h 15m ～25m and 12h 30m ～40m on the upper record in Fig. 2. It is to be noted that during 20 ～ 25 minutes the BPV signals can be found in preventing the minute signals signals of ]JY dropping down to the noise level. This record revealed that the c.s. (call (call sign) of BPV was modulated by 1 kHz, regardless of non-modulation accord- ing ing to Fig. 3. The lower record in Fig. 2 was obtained when the ship was sailing near the Philippines Philippines (15° N, 130° E) on December 4, 1968. The interference with BPV is seen seen about 1 hour before and after 20h.