Hi Gordon!
Because AO-51 is the most reliable satellite in terms of actually finding and working it. SO-50 seems to be almost impossible to lift, and the linear transponder ones require extremely expensive radios. You can work AO-51 with an el-cheapo dual-band handie and a homebrew antenna, and you can work /P really easily because you don't need a rotator or satellite tracking software.
SO-50 isn't impossible, but your receiver and antenna system need to be able to deal with weaker signals than you hear from other FM birds. SO-50 is transmitting at 250mW, and it gets regular workouts on passes over here. AO-51 is now running with more power on the downlink than usual, which will make the difference between it and SO-50's downlink more noticeable. PL tones are also mandatory on SO-50, to turn it on (transmit briefly with 74.4 Hz) and to talk through the satellite (67.0 Hz).
I'm not going to rush out and buy a VHF/UHF SSB rig just to work the odd pass, especially since I've never heard anyone on the linear birds. I don't know if VO-52 works - I've never even heard its beacon - and AO-27 is only ever enabled over the US, making it useless for most of the world. It would be great to attempt a QSO through AO-7 but again I'm not going to go and buy a rig that costs as much as a car to do it.
I would not characterize a Yaesu FT-817ND and Kenwood TH-F6A (outside North America, TH-F7) as "extremely expensive" radios. Sure, these two radios are more expensive than a single 2m/70cm FM HT, even more expensive than the new TH-D72A HT, but not like the prices were on all- mode 2m and 70cm gear were in years past. I regularly work the linear birds with either two FT-817NDs or one 817 and a TH-F6A receiving the downlink. With an FT-817ND, you also get a radio capable of QRP HF and 6m operation. The 817s have been in production for a decade, so you could also look at picking up a used 817 (or two) to try SSB on the birds. The 817s have a CAT control port on them, so they can be controlled with software like SatPC32. Two 817s can be controlled by SatPC32, if you are looking for an all-mode full-duplex satellite ground station with those radios.
Besides an 817, you could also look at radios like the IC-706Mk2 or Mk2G, IC-7000, FT-857, FT-897, etc. You'd need a larger battery to run them than you would an 817, but all of these are capable of being used for SSB satellite work.
VO-52's beacon is just a carrier on 145.936 MHz. It is on all the time, and the VO-52 downlink is easy to copy. It is a great satellite for someone interested in starting out on SSB via satellite. AO-27 is available on daylight passes over the Northern Hemisphere, not just over North America. If the web site is accurate, you can get an updated schedule for AO-27 for the upcoming 24 hours at:
You can also download a program that shows when AO-27 will be on for any particular date from:
http://sites.google.com/site/ao27satellitescheduler/
The SSB birds are not as busy as the FM birds, but you can find activity on them. Many will work SSB with computer-controlled radios or antennas/rotator, but I - and others - do this without the benefit of computer control. It may be "old school", but with practice it is possible. If you are looking to work these birds from a portable station, that is entirely possible. I do that all the time - at hamfests, parks, from the back of my truck, with my gear laid out on the roof or trunk of a rental car, wherever I happen to be. All of my satellite station, excluding antennas and items deemed unsafe in a carry-on bag for air travel, fit in an old laptop bag. The antenna and other stuff go in a duffel bag that gets checked for air travel. You don't get the numbers of QSOs on an SSB bird that you might on AO-51, but I have fun with it.
73!
Patrick WD9EWK/VA7EWK http://www.wd9ewk.net/