[TowerTalk] OR-2800PX Point and Shoot?

[K8RI on TT]

On 3/3/2011 3:19 AM, Jim Thomson wrote:
> Date: Thu, 03 Mar 2011 02:22:20 -0500
> From: K8RI on TT<k8ri-on-towertalk at tm.net>
> Subject: Re: [TowerTalk] OR-2800PX Point and Shoot?
>
> Point and shoot?
>
> 73
>
> Roger (K8RI)
>
> ## The GH  box's  have a large knob on the front panel....marked off over 360 degs.
> The digital display always shows the CURRENT  heading.    You simply crank the knob
> over from say ZL land  to  say EU  [ 30 deg from me].... and sit back and watch the show.
> After a brief pause, the rotor will ramp up in speed..like a 9 x speed auto transmission, and once up

I'd hardly call that "point and shoot", although it is the most basic 
rotator function and the only available with the early TV rotators.  My 
PST-61 has a feature where you just punch a button to get you "close". 
To me that is "point and shoot".

> to max speed..whizzes  over the pole to EU.   When it gets  20-30 degs  b4 EU.. it starts the slow down sequence
> and ramps  down  from speed's 9, down to 8-7-6-5-4  etc... till  it's  barely crawling along..then stops..exactly at
> 30.0 degrees.    It will put it within .1 deg  of where u want it every time.

0.1 degree of the heading with a beam than may have 30 or 40 degrees 
between the half power points?
Even with the largest of HF physically rotatable arrays, "off that a 
way" is far more accurate than needed.

Even with large VHF and UHF arrays (except for large dishes) 2 or 3 
degrees is great.

> ##  once u start cranking the knob, the display will also display the  new heading, or where ever the knob is cranked to.
> That way you can dial up a specific heading...like 34.6 degs  if you like.   It's  all automatic, no fuss, no muss,  and with the
> ramp up/down... you don't trash gears etc.   On ramp up, ur not slamming all the torque on at once.

I agree with the ramp up and down, but hate the thought of any one 
using  PWM control any where near my station.

>   With the PWM
> motor controller,  it ensure u get max torque, even when rotating at slow speeds. PWM  just applies  max  normal
> voltage.. but with gaps  between pulses.   IE:  they alter the duty cycle to control the speed.   Since each pulse gets max voltage,

And has the potential for creating maximum RFI.
I'm looking at geothermal H&V for the house. The estimate cost per year 
here in central MI where it's presently 7F is about $360 per year.  That 
heat and air conditioning for a whole year.  It sounds cheap until I 
figure it currently costs a tad under $700 per year with a more 
conventional H&V system.  That means I'd have to be 120 or 130 by the 
time the thing saved enough to pay for itself and that's with some 
pretty good rebates and tax incentives.

> that scheme  minimizes any loss of torque.

That'd I'd argue.  For 100% torque you need 100% current, 100% of the 
time.  You can improve it by using a massive armature in the motor.  You 
only have the 100% torque for the duration of the pulse plus the 
mechanical inertial which at slow speeds is no where near what it would 
be at full speed.

>   IE; if u just reduce the operating voltage to slow down a dc motor, sure it will run slower,
> but the torque will also  drop off really fast.    The PWM scheme gets  around that.
>

It's an improvement, but it does not eliminate the torque fall off.

> ##  Not having ramp up/down capability is a real detriment to rotor life.  It makes me cringe when u see a heavy array, that has been
> turning at 1 rpm  for 30 secs..then comes to a crashing halt..yikes.  Sorta like driving down the highway at 60 mph,....then shifting into park.

Let it coast. <:-))  On second thought rotators with wedge brakes and 
large antennas do not go well together.
I operate rain or shine, wind or calm.  I hit the brake release on a 
Hygain HDR-300 and though the meter had shorted as it just snapped over 
against the peg.  It went right by the limit switches and tore up 5 runs 
of coax.

There are a lot of good rotators out there that use the equivalent of a 
"step start" and stop and do not need brakes.  Nearly all of the dual 
worm gear rotators seem to do quite well.  Although I like the PST-61 
I've been using parts, are expensive and were slow delivery. Now they 
have a stateside supplier that may have improved.  They are still kinda 
pricey though.    OTOH most, but not all of the parts were standard 
automotive.   I think the next one with be the Canadian AlphaSpid.  They 
were going to come out with an even larger version. I don't know if 
they've done that yet of not.

I believe MFJ was going to be selling them state side, but I haven't 
found them in the catalog yet.

73

Roger (K8RI)