Re: Az/El Rotors

[al lawler <alawler@xxxxxxxxxxxxx>]

Bill,

  I haven't seen the 73 article, but I  used Gemeni
(orbit-360) rotators with a homebrew computer interface for
quite some time on the pacsats.   (They're still outside,
but I'm no longer on any satellites.) Overall, they work
well, particularly if cost is a factor,  but there are
a few caveats:

  -  They aren't particularly durable.  I've seen them move
     my snow covered antennas on a -20 degree morning,  however,
     at least one gear in the gear-train is plastic,  and they
     do wear out in continuous LEO use.  (They would probably
     last forever in an ao-13 only type of use...)  On the 
     other hand,  they are cheap enough to just replace when
     they go bad.  The biggest antennas I used with them
     were a 2x7 2m yagi, and a 2x8 70cm yagi.

  -  The position voltage range is 0-3.2v, and the range is
     backwards from the gr5400,  which could cause you 
     difficulty in interfacing to some pre-existing control
     software.

  -   They don't have limit switches.  If the rotators stalls,
      it will sit with power applied until you intervene.  
      (This doesn't seem to damage the rotator for short 
      periods of time,  but makes unattended operation a bit
      less desirable.

  -   The calibration drifts with temperature.  I've also
      seen the calibration drift a LOT when frost gets
      into the position sensing pot.)

  -   The control cable supplied with them is garbage. Don't
      use it.  It's too small a gauge, unshielded,  and 
      the insulation breaks down with weather causing 
      potential shorts between the wires.

  -   The center "hole" is smaller than you'd expect.  I
      don't think it'll take 1.5" pipe.  (I used Ash 
      closet-rod, which is a bit skinnier, and it worked
      fine.)


  In summary,  they are a great low-cost way to get computer
controlled AZ/EL, if you are willing to tinker a bit.  I would,
however, recommend mounting them somewhere easilly accessible,
since you may end up having to replace them more often than
some of the more expensive models.  (I have mine on a ground
mounted tripod, which worked real well.)

  -al
  WB1BQE



Bill Richarz wrote:
> 
> Was looking at an article in Jan. 73 magazine, page 32, using a pair of
> Gemeni rotors.  Anyone got any feedback to that article?
> 
> Was also wondering how large of an antenna could it be expected to hold?
> 
> Also, read with great interest the article in Feb. QST using the Drake
> converter with modifications...any comments on that?
> 
> How about the  SB-32DXC parabolic antenna  from R. Meyers
> Communications?
> 
> Been awhile since I've been into the Amateur satellites, but my
> interested was hightened ...enough so to join the list.
> 
> Will be reading with great interest, and possibly putting up a station
> here.
> 
> Thanks for the interest.
> 
> Bill, N4DH
> 
> ======================================================
> Bill Richarz <N4DH> ex WA4VAF
> Internet:            wricharz@charlotte.infi.net
> Packet: N4DH@W4BFB.#CLT.NC.USA.NA
> 10035 Little Creek Rd.
> Charlotte, NC 28227          Phone: (704) 545-9368
> Packet:       N4DH@W4BFB.#CLT.NC.USA.NA
> HomePage: http://www.charlotte.infi.net/~wricharz
> Alternate Email:    n4dh@juno.com
> =========================================================