Satgen370 Satellite Phone QRM by GM4IHJ 27th April 1996 A worrying situation is developing in the new field of mobile telephone satellites, which could have parallels for the radio amateur microwave bands. The frequency band 1610 to 1626.5 Mhz has been allocated to these satellites. Subject to their not causing interference in the radio astronomy band 1610 to 1613.8 Mhz ,which covers the frequencies produced by the important hydroxyl radical , whereby radio astronomers can study the location, structure, density and velocity, of the large molecular clouds in our own and other galaxies. Unfortunately these natural frequencies are fixed , so the astronomers cannot move . So it had been thought that mobile phone sats would use the adjacent frequencies only for uplink. In fact most companies appear to accept this , with in one case ( Globalstar) already accepting that their phone will locate themselves using GPS and will then be directed to avoid astronomy frequencies if they are anywhere near a radio observatory Unfortunately it will not be that simple for everyone. The Iridium satellite consortium are proposing to use the 1610 to 1626.5 band for dowlink from their satellites , as well as uplink. Which will naturally make the problem much more difficult for radio astronomers. So the Iridium group have made several suggestions :- a. Radio astronomers should listen in the gaps between the phone signals. Which will be difficult as the downlinks will have at least 72 Khz of doppler . In addition as radio amateurs who battle with Pave Paws radar in the 435 Mhz region will know , hunting weak signals against powerful interference is a waste of time and effort, and you get no help from the RSGB, either before or after the interference appears, however long you have been using the band or however much money you have invested in equipment. b. The Iridium group will guarantee 4 hours a day free of phone traffic. Which might help but for the fact that Galactic targets keep sidereal time and as seen from a spinning earth only appear for a few hours a day, which will not coincide with the phone companies break . c. The Iridium group suggest they will put beacons near observatories warning phone users to avoid Astronomy channels ( see the note below regarding the Italian problem which confounds this sort of strategy). That agreement is necessary BEFORE satellites go up is shown by :- a.Russian GLONASS sats have disturbed radio astronomy for years. Three years ago the Russians agreed to shift them. It will take 10 years . b. Italian commercial broadcasting recently got access to 1660 to 1670 Mhz " subject to non interference with radio astronomy ". In practice this means 20 plus station are now seriously disrupting astronomy. So far attempts to shift the offenders are taking months and all the while more stations are adding to the confusion. If there is a message here for radio amateurs , it is that, it is too late to complain once the commercials are there. What ever promises are made before the commercials come on the band are quite inadequate unless they are firmly forbidden to use sections of the band and very serious attention is given to the worst case scenarios produced by commercial downlinks.