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icarus 8, 503-507 (1968) Forward Transmission from Meteor lonization L. W. EDWARDS Postmaster-General’s Department Engineering Branch, Hobart, Tasmania Communicated by J. G. Bolton Received October 23, 1967 Results of observations of forward transmission at 39.3 MHz over a 320-mile path are given for a 12-month period from October 1965 to September 1966. Max- imum and minimum count rates show no significant seasonal variations although large increases are evident at the expected times of the Geminid and Leonid meteor showers. A large number of long duration reflections are evident which, due to their regularity, are difficult to associate with transient meteor ionizations. They appear to be related to natural and artificial satellites. IL. MerHop Observations of signals at 39.3 megahertz (MHz) were made at Hobart Tasmania (Lat. 42°53’ south, Long. 147°19’ east) from a P.M.G. Radio Telephone Transmit- ter located at Tanybryn, Victoria (Lat. 38°40’ south, Long. 143°43’ east) during the period October 1965 to September 1966. The receiver is normally far below the radio horizon of the transmitter 320 miles to the north, but when sufficient ionization is pro- duced at a suitable point a signal is received at Hobart. The transmitter had a power of 200 watts feeding an aerial array of 32 half-wave elements in phase, with 32 para- sitic reflectors, directed towards Tasmania. The receiver used a single horizontal dipole antenna and was held on frequency by crystal control. A noise limiter and narrow- band audio-frequency amplifier gave good discrimination against unwanted noise. In- strumentation was arranged so that signals above a certain threshold value gave only one count independent of duration, counts for each minute were recorded on a chart while total daily counts ending at 2000 hr each day, and the hourly count between 0500 and 0600 hr local time were recorded on separate mechanical counters. Regular equipment sensitivity checks were made. Il. Mereor Counts There is considerable scatter in count number from day to day, especially among the dawn values. Average monthly counts which are plotted in Fig. 1 show no sig- nificant seasonal variations. During the year of observation the count rate declined in an irregular manner. This cannot be ac- counted for as a decrease in system per- formance as regular checks indicated that equipment stability was good. The minimum count rate is near dusk. The ist and 16th days of each month from September 1965 to September 1966 were sealed for hourly counts from 1500 to 2100 hr. These were averaged and are shown in Fig. 2. - The daily minimum tends to appear ear- lier during the winter months while the average for the year shows the minimum between 1800 and 1900 hr local time with fairly small scatter. These results may be compared with those of Ellyett and Keay (1963) who used direct radar echo techniques. The minimum count rate obtained by me is similar to theirs, however my maximum count rate is several times higher. The forward trans- mission detection method appears to give a higher ratio of dawn to dusk. cotint rates. 503