Re: [amsat-bb] G-5500

["Roy Schulz" <VE7BPB@xxxxxx>]

Hi Ben and all,

I have been following the discussion in regards to speed control of the
g-5500 and thought I might add my 2 cents.

I have a 6 foot mesh dish and a couple of yagis mounted on my az/el system,
which uses the old Kenpro KR-400/500 rotor pair. I am using a G-5400b
control box with them.

I found that running the rotors in stock form caused considerable aiming
errors with the dish, which I attribute to the rotors themselves
overshooting the mark when they are moved, either manually or automatically.

 I solved this by building a pulse-width curcuit into the control box which
does nothing more than switch the AC line going to the rotor motors at a
rate that I can set with a potentiometer. I used a solid state relay to
break one of the leads coming out of the 24 Vac transformer that runs the
rotor motors, and switch the relay with a simple 555 timer circuit of the
type used for light-dimming, etc.

I added an LED indicator on the front of the control box and just adjust the
speed pot for a fairly slow blink rate , typically about once per second,
when I have gotten the antennas turned in the right general direction.

The accuracy of the aiming has been improved dramatically, and the
mechanical stresses on the whole rotor system are much reduced because the
antennas now move in very small steps, rather than trying to whip around at
full speed to accomplish small corrections.

I think that for anyone that has a large array or needs better pointing
accuracy with standard rotors, it is the easiest and most cost-effective
modifiaction you can make.

regards,

Roy VE7BPB
Vancouver



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