[amsat-bb] Re: Lunar Architecture Moon Base
Edward R. Cole
al7eb at acsalaska.net
Sat Dec 9 00:37:32 PST 2006
At 11:18 AM 12/8/2006 -0500, Jason White wrote:
>Edward R. Cole wrote:
>> With a manned base I would offer that a tracking antenna is practical.
>> Perhaps it could be made piggy-back to NASA's comm system? Of course there
>> is always electronically steered arrays. Perhaps a quad of dishes pointed
>> to cover the 10-degree area of lunar sky the earth moves thru? Then only a
>> 4-way coax switch to track. The 8-foot dish on the Moon has a 3.65 degree
>> bw at 2400 MHz.
>> Ed - KL7UW
>The thread on a lunar based transponder has me wondering.. How were the
>comms with the Apollo missions done? What frequencies/modes? Did
>amateurs and utility listeners of the time copy much of anything from
>the moon while man was there? Did they have these same problems or did
>the fact that Eagle was in orbit solve them?
>I've heard the crackly "That's one small step.." recordings, and it sort
>of sounds like SSB, but I had never really thought about it before. Now
>that I think about it, copying that signal would probably have been the
>rarest utility DX ever!
>From memory the Apollo had Collins Radios that were UHF (something like 280
MHz) and the astronauts set up a dish on the Moon's surface for 2.2 GHz
(the then NASA Unified S-Band...nominally Tx=2115 and Rx=2295 MHz). This
band was shared with the unmanned spacecraft such as the Mariners,
Pioneers, and Voyagers. I believe you are correct that it was SSB
(probably with inserted pilot carrier for AFC). Does anyone remember the
lunar rover with its "umbrella" dish (about 6-foot)?
I worked at the Goldstone Tracking Facility from July 1971-April 1976, and
was there in time for the last two Apollo missions. My job at Goldstone
was as a DSN mw receiver engineer at a 85-foot dish (26m). My boss set up
a ten foot comm dish in his front yard and using a diode mixer with a
signal generator as LO, detected the 2-GHz carrier of the orbiter as it
circled the Moon. It was fascinating to hear the signal and the Doppler
shift as it orbited and lost signal for about 20-min as the orbiter went
behind the Moon. That was too small and poor a receiver to recover
modulation, so we did not hear any voice. At work they played the live
Apollo audio over the PA system, so we got to hear them all day. I
revisited Goldstone taking a tour in the fall of 2001 (25 years later) -
I believe some hams were able to pick up the Alsep signals, as well. My
only ham mw operation back then was in 1974 on 3300 MHz making a 100+ mile
shot using a 6-foot dish and 100mw klystron with WBFM. I was a member of
the SBMS during those years (and am again, having recently re-joined).
Ed - KL7UW
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