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@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)
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