[Namaste-dev] Re: DBS dish mounts
wbblair3 at yahoo.com
Thu Jun 26 15:39:52 PDT 2008
> The mailing list is archived, so you needn't remain in the dark about what has > already transpired.
> You can find a link to the archives by visiting the URL that's at the bottom of > every message.
>> here's an inexpensive home-brew and highly stable DBS dish mount
> Pretty nice.
> There must be some extra noise due to aiming the feed at hot earth instead of cool > sky. I don't know how big an issue that would be.
After browsing the archives, I gather that everything is still very much at the experimental stage right now, so I guess my input should be considered as just a suggestion to consider low-profile, low center of gravity/pressure mounts at some point in the future when the dish mount is finalized. I'd read that emergency comm was one of the goals of Namaste, so I’d guessed that resistance to high winds would be an especially desirable characteristic. A low dish mount would make it more susceptible to the odd wandering bipedal microwave attenuator bankrupting your link budget and exposing itself to ionizing radiation, but a tiny, marked-off radhaz zone would fix that. And if noise is a problem, the dish could be mounted upright at the cost of a slightly higher center of pressure and gravity.
I'd planned to use a larger version of this sort of low-profile mobile mount with a 36" DBS dish for AO-40 at 2.4GHz. The az-el mechanism was to be a low profile Dobsonian mount with a circumferential azimuth bearing to prevent the dish from being lifted off of the mount by a wind gust. Tracking would have been done manually using left/right, up/down switches to activate the motor drive and peak the receive signal. Friction drive would have been accomplished via two heavy-duty $12 surplus geared DC motors with a very high gear ratio. Soft rubber rollers (also surplus) on the motor shafts would roll on the periphery of the plywood disks associated with the Dobsonian bearings. A high-friction surface on the disks was to be made using an epoxy/coarse sand mix painted on in an appropriately wide strip. Since this was a mobile mount that would be in close proximity to the operator, dish positional feedback was to be via eyeball.
I mention all of this because the Dobsonian mount is a simple, low cost az-el mount that is easy to make from common materials using simple power tools. It can be made to precisely auto-track moving targets using stepper motors and belt drives. Perhaps with a high-apogee satellite like Eagle even manually-commanded motorized tracking would be acceptable? From what I've read, the planned apogee for Eagle looks close to or even higher than that of AO-40.
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