[NLRS] Elevation rotators for small stuff

[Dr. Gerald N. Johnson]

On 9/4/2013 11:54 PM, Doug Reed wrote:
> I'd say that having the dish mounted to a car or truck but without any
> sort of bracing against ground will mean the dish changes elevation
> every time you move around in the vehicle. That was one reason I
> wanted a motorized elevation control, to keep the dish on the horizon
> as I moved or the dish turned. With a vehicle mounted dish, I assume
> the platform will NEVER be level and every adjustment of azimuth will
> also require an elevation adjustment.

Being less than 10% of the rated load of my truck, I don't detect moving 
around in it has any significant effect on its suspension. Golf maybe 
but still its rated at 1600 pounds maximum load so 190 doesn't seem to 
move it much either. Neither is sprung like the vintage Buick. Mostly I 
planned to operate standing alongside the vehicle, not in it because 
sanding along side I can reach the antenna, inside it all has to be 
remote controlled.
>
> With a remote mounted inclinometer on the dish, a computer program can
> adjust the dish as azimuth changes, or when I get in or out of the
> car.... I can buy one of those for $20 or less with careful shopping.
> I haven't yet looked for a remote electronic compass that has 1 degree
> resolution.... I'm not worried about magnetic declination since the
> computer program can  always adjust for that.

A Sears electronic level reads out in degrees with 1 degree resolution 
and its not hard to capture that data remotely. There was an article in 
MUD2008 I think about that.

Local magnetic declination is a considerable problem in some locations 
like the UP full of iron enough to have mined it, as well as the north 
side of Lake Superior. To say nothing of cars with sturdy speakers for 
loud sound systems or substantial electric motors like a hybrid.

And there are similar spots in SE Missouri near Iron Mountain and 
Ironton. It was reported during the civil war that some outcroppings on 
Iron Mountain were so magnetized they would hold a rifle. Chasing road 
history in the area, I found an 1840 vintage road survey done with 
compass and chain. I plotted it to the same scale as a modern 
topographic map with AutoCad. For the eastern two thirds (Fredericktown 
to Ironton) the plot crosses creeks where the topo map shows bank cuts, 
but as it gets within 5 miles of Iron Mountain, it leaves the creek and 
river bottoms and climbs straight up over a hill that today a jeep can't 
climb. I'm sure the route stayed in a valley but the mountain deviated 
the compass too much and that's not magnetic deviation detail thats 
readily available.

Once the azimuth and elevation is found for a rover pack set of contacts 
the antennas only have to remain still for about 3 minutes for 8 or 9 
stations on the hill. Contacts roll off fast when the path is good.
>
> With something small like a Raspberry Pi or Aduino kit, a lot of the
> positioning could be done at the dish. But it might be easier to read
> the sensors and drive the positioners directly from a laptop in the
> car.

Such are the trade offs, if the laptop has adequate interfaces not all 
USB or the sensors and drives do have USB, then either works.
>
> I considered a lazy susan bearing race before but was unsure how
> stable and sturdy they would be since it really must not tip and tilt
> in the wind. Maybe it could be made useful for rough aiming if you add
> multiple clamps to hold it tight when pointed in the general
> direction. I think Bob W0AUS tried something like the lazy susan many
> years ago and dropped it. It would be a lot easier to mount the dish
> on a pipe attached to a U100 rotor, if it has low enough backlash....

There are lazy susan bearings barely able to handle the rotating shelf 
in the middle of a Chinese restaurant table and the one I picked up 
rated at 900 pounds load. The heavy one is built pretty good. The spacer 
blocks and ratchet clamps would take all of any slop out when locking 
the direction. The rotor raises the dish more into the wind when moving 
and takes some sort of pipe structure that can slip, bend, and slide 
connections, where the two sheets of plywood provide most of the roof 
rack spanning structure. The plywood is easily stiffened with 2x4 under 
the bottom and above the top ply. My U100 has a poor read out and I 
don't think its controllable well enough for an 18" dish. Much less a 
larger dish. The larger dish needs the servo with a good read out. I 
don't know if the heading information is available on the RS-232 port 
but my hand held GPS does display the direction to Buck Hill graphically 
and in a numeric display. Finding north while roving is the limiting 
factor. A minute of beaconing usually solves antenna aiming, unless the 
gentle vespers blow the tripod over before its my turn to make contacts. 
Its not sure the path either great circle or straight line as computed 
by the gps is the path the tropo signal is using. Its quite practical 
for the first beaconing station to illuminate a scattering space with 
enough scattering to make contacts without that being along either 
geographic line or the lowest elevation. On 432 I've heard stations like 
NW Indiana working MSP but the Indiana station was only copyable when my 
antenna was looking NE, not just south of east which was the direct path 
to that part of Indiana. Just that the scattering volume was way off the 
direct path because that's the volume he was illuminating.

If the first station to beacon on any given path had the information and 
the control to pick the lowest altitude and most direct route, the odds 
of strong signal would be better. But that presumes a uniform atmosphere 
which though assumed by weather forecasting models is not always the 
case. That winds, temperatures, and moisture contents sometimes vary on 
a very small scale over a mile or less (as observed around low clouds 
many days and more strongly at fronts) and those gradients cause bending 
of the microwave signal from the straight line or great circle and 
lowest elevation path. For the distances we usually work, the great 
circle path and straight line plotted on a Lambert or Poly Conic 
projection are probably indistinguishable.
>
> 73, Doug Reed, N0NAS.
>
>

73, Jerry, K0CQ