Satgen266 Sporadic E versus Satellites and Moonbounce by GM4IHJ 30 Apr 94 BID of this msg is SGEN266 Please use this BID if you retransmit this msg The Northern Hemisphere summer Sporadic E season is coming. From May to late June increasing numbers of daylight hours will feature relatively dense patches of ionisation in the lower ionosphere. In June/July events will last for several hours for stations located between latitude 30N and the north pole. Then towards the end of July events will become less frequent, tailing off , almost to zero, by September. There is a small weak winter season from mid December to mid January each year. While Southern hemisphere stations get lots of SpE in their summer from November to February. So when SpE is around terrestrial DXers can expect plenty of good daylight DX on 50 and 144 MHz, out to distances of 2000 kms or more. For satellite and moonbounce users the picture is much less happy. To access a satellite your signal must get up through the ionosphere , then on its return trip back down to you your signal must again get through the ionosphere. At 145 MHz and to a lesser extent 435 MHz, Sporadic E can make this ionospheric transit very difficult, if not impossible. Worst hit are the 145 up. 435 down satellites mode J, a group which includes almost all the digital store and forward Pacsats / Uosats / Fuji and the Korean sats. So do not be surprised if your afternoon attempts to access these satellites come to nothing. Less affected are the mode B 435 up, 145 down satellites of the mode B type. With them you should have no great problem accessing the satellite but the downlink to you may be poor. Several procedures can be used to counter SpE :- a. SpE rarely blocks the whole of a satellites pass. It usually affects the southern half of the pass much more than the northern half. b. Avoid the afternoon passes. SpE is at its worst between 1300 and 1600 local time. c. Satellite passes at high angles of elevation passing close to your station have the double advantage of short signal paths = strong reception , and , better penetration of SpE by high elevation signals. Eg Spe was responsible for the rapid abandonment of 137 MHz for weather geosats when it became clear that their low elevation signals into northern Europe just never got through in summer. Last but not least SpE can seriously affect moonbounce signals as they come up and down. The effect of SpE is rather like that of fog. Eg on a clear night the lights of an approaching car are sharp spots. But when fog is present the lights become broad diffuse "defocussed " blurrs. So like fog most of the signal misses the moon if SpE affects the uplink or, the ground station antenna fails to collect most of the signal if SpE affects the downlink. Please remember that only one station in an EME QSO needs to be affected by SpE , for the contact to be lost. When one station is in daylight and another is in darkness, ie dark station no SpE. It is often difficult for the operator in darkness to appreciate the problem facing the operator in daylight. This situation is most unlikely in respect of satellite operators but it can seriously affect longer range EME operations. So be warned . When Uosat or Lusat simply refuse to acknowledge your 2m uplink, but you can hear the 70 cm downlink quite plainly . Suspect that Summer SpE is the culprit , and try again latter on the more northerly part of the pass. 73 de GM4IHJ @ GB7SAN