[amsat-bb] Extended info about calibrating your LVB tracker and G5500 rotor

[Burns Fisher]

For some reason the 5500 and the LVB in my system got out of whack.  It may
have been when I switched from "450 degree azimuth" mode to "flip" (i.e.
180 elevation) mode.  I don't know.  But even after calibrating the LVB
several times, it would not set the elevation to 180 and setting it to
90 degrees ended up something like 15 degrees off.

I took the LVB cover off to access the connections to the 5500, and
discovered that far from sending an analog voltage of 2 to 4.5V to equal 0
to 180 degrees as the Yaesu docs say, the 5500 was sending 0V to 5.5 or
so.  A bit more work found that the LVB did not respond to much more than
5V.  I assume that is the reference voltage on the A/D converter.

A look at the schematic on the 5500 found a pot that appeared to adjust the
voltage to the LVB independently of the meters.  There is zero
documentation, but the back of the 5500 case actually has 4 pots:  Max
meter and Max output for both Az and El.  So holding my breath, I turned
the Max Output pot and sure enough the voltage to the LVB went down.  I set
the rotor elevation to 180 degrees (by eye) and then turned the pot till
the LVB readout just started changing.  Then I used the LVB calibration
procedure to match that location to what the LVB thought was 180.  Voila!
 90 is now pretty good too.

In retrospect, this is not inobvious; however the fact that the Yaesu docs
say 2V to 4.5V and the fact that the LVB was not responding beyond a
certain elevation required some investigation.  Hopefully this little post
will save someone else from having to repeat the investigation.

73,

Burns, WB1FJ