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Re: [TowerTalk] OR-2800PX Point and Shoot?

Subject: Re: [TowerTalk] OR-2800PX Point and Shoot?
From: K8RI on TT <>
Date: Thu, 03 Mar 2011 04:20:19 -0500
List-post: <">>
On 3/3/2011 3:19 AM, Jim Thomson wrote:
> Date: Thu, 03 Mar 2011 02:22:20 -0500
> From: K8RI on TT<>
> 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 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 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.


Roger (K8RI)


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