karn@petrus.UUCP (05/17/85)
This is a question that's bugged me for some time. Those of us who are space junkies have gotten used to listening to space-to-ground audio links that are, shall we say, somewhat less than "telephone quality". While the overall intelligibility has gotten better over the years, it is still worse than I would expect. In the case of the space shuttle, which uses digital transmission (delta mod) for its primary (non-UHF) audio links, I had assumed that the noise you hear when an astronaut opens his mike must be due to things like ventilating fans on board (after all, air doesn't move by convection without gravity). However, when Owen Garriott made his famous DX-pedition, using the same headset connected to a 2m FM handie-talkie, his audio quality was absolutely clear -- virtually no transmitted noise or distortion. If I hadn't already been familiar with his voice from things like interviews and press conferences, I would have suspected a hoax. So where does all the noise come from in the NASA chain? Do the orbiter avionics use large amounts of speech compression or clipping, or what? Should we hams offer to replace all of their communications gear? Phil
wmartin@brl-tgr.ARPA (Will Martin ) (05/18/85)
A good question, and an opening for a topic I had been meaning to post for some time now, and always forgot to... What has the radio equipment available to the astronauts been, over the history of the manned-spaceflight program, and especially now, in the Shuttle? As a longtime DXer, I have always wondered what it would be like to have radios in orbit, and be able to tune around and see what I get. Can the astronauts do this? I would expect that you'd get some shortwave and medium wave signals -- the portion that punched through the ionosphere and wasn't reflected, and that part radiated straight up, which doesn't get reflected, as you pass over those antennae. Higher frequencies would go right through the ionosphere, of course, but I'd expect to get a mixture of everything on the hemisphere transmitting on that particular frequency (with the closer transmitters dominating, so it would constantly change as the receiver orbits). So, do the astronauts now have general-coverage receivers that they can tune, or is all the radio gear fixed-frequency and dedicated to the mission? What about video reception? Do they have PAL and SECAM and NTSC equipment to look at TV signals from all over the world as they orbit? I like to think of getting a mix of every US station on channel 5 at the same time... surrealistic TV DX! The latest episode of the PBS "Spaceflight" series mentioned how deadly bored the Gemini astronauts were during scheduled sleeptimes (when they weren't sleepy) and during the last part of long-endurance missions. I DX at times like those -- did they have the chance to? What about antennae? Spacecraft being metal cans, it probably is necessary to get some sort of antennae outside the craft and the signal fed through. Are there spare or unused antennae that can be used for recreational radio reception? What about HF -- are there reeled-out longwire antennae on the Shuttle for HF, or is that portion of the spectrum ignored? (Could you receive LF or VLF from orbit, or are those all ground-hugging signals?) Any NASA types out there who have info on the the radio-related aspects of the space program, please post info on this! Inquiring minds want to know! Regards, Will Martin USENET: seismo!brl-bmd!wmartin or ARPA/MILNET: wmartin@almsa-1.ARPA