Satgen 569 SatSignal Reception 5 by GM4IHJ (BID SGEN569) 2000-02-19 At the end of the 1970s, Radio Amateurs were restricted in what frequencies they could listen to, by , their ability to build or not to build, their own frequency converters. Commercial equipment for frequencies above 200 MHz , was simply not available at reasonable prices. But now 20 years later, receivers are available for all mode reception up to 2 GHz , and a number of attractive surplus converters or commercial narrow band converters are available , to help us explore ever higher. So , are all things bright and beautiful on mode S downlinks , and are we ready for even higher frequencies? The answer is probably a firm NO. At least for the first few years of Phase 3D, after which hopefully as many radio amateurs eventually did with 430 MHz, there will be a gradual increase in numbers using the higher bands. The first problem they will face, will be doppler shift. Copying an S band 2400 MHz downlink from a low earth orbit satellite, is simply not fun unless you have AFC, automatic frequency control. But you should be able to practice on future high flying Molniya elliptical orbiters. Where the slow change of range at apogee orbit high point, produces a slow rate of change of the frequency of the dopplering signal. Reducing Ddot doppler rate to managable proportions. On Ao13, this operator found CW was much easier to use even off apogee as doppler rate rose, than SSB which requires much more precise tuning if the signal is to be readable. Indeed frequent retuning of SSB signals whilst you also have to watch antenna heading and elevation is not at all easy. So CW was this lazy mans choice. While PSK/FSK digital traffic exchanges should be relatively easy given the AFC capability of the modems used. Provided there is no break in transmission , ie the stations in contact use different quite separate parts of the frequency band But for some people digital message transfer is far too impersonal for real amateur radio. At which point therefore , it is perhaps convenient to ask whether amateur radio will go over to digital voice on the higher frequency satellite bands. We happily accept this on mobile phones. and satellite mobile phones. Maybe someone is preparing for this ? Though experience here with digital TV ( satellite and terrestrial) , plus digital satellite mobile phones does suggest caution. Noting that the big problem here seems to be ignition interference, with digital equipment apparently very sensensitive to this still quite common problem. Which may affect analog systems but does not stop them in their tracks. A feature which just one unfriendly over tuned motorbike or, car which has seen better days , can readily demonstrate if you live near a busy highway or worse have a corner site where these unmentionables stop to check the road is clear, blasting your reception for what seems like hours. So perhaps we should proceed digitally higher with caution , and not forget that there are still some awkward propagation inhibitors which lie in wait for us, as will be reported in the next satgen .