Hi John, N7JK
You are correct ,the Rotor wiper on terminal 1 is the ground reference but the wiper is connected to ground via the potentiometer arm wich is a cogged copper-berillium strap compressed in to a boss casted in to the internal top of the aluminum hood.
The hood in his turn is connected to terminal 1 through the ball bearings and the lubricant grease wich is not a good and stable conductor.
I don't recall if the wiper is directly connected or not to terminal 1 via another fized connection but looking at the manual I can see only 2 wires going from the end of potentiometer to terminals 3 and 7
If possible it would be a good idea to add and additional ground strap between the wiper and terminal 1
From the electrical point of view the voltage available from terminals
3 and 1 is a zener stabilized +12 volt CD and the fixed 10 k resistor in series to a 10 k trimmer is used to divide the voltage by 2 in order to get a maximum voltage of 6.5 volt from the wiper of the trimmer and ground to protect by overload the A/D converter.
The only problem remain the backlash between the potentiometer arm and the boss of the hood i.e. the antenna rotates by say +/-10° and you cannot see no indication change in the indicator (I) and of coarse no feedback voltage is developed after a PC command is received by the motor so that the dead zone is too large and position instability i.e. "ping-pong" of the antenna is possible.
73" de
i8CVS Domenico
----- Original Message ----- From: "John Kopala" [email protected] To: "AMSAT-BB" [email protected] Sent: Monday, December 04, 2006 12:19 AM Subject: [amsat-bb] TrakBox Interface to HAM-IV Azimuth Rotor
Thanks Dom,
Cool. I think I've got it.
In summary, the Rotor wiper on terminal 1 becomes ground reference and terminal 3 becomes the indicator voltage. The resistor and pot are used to scale the voltage to the desired range. And no problems with a ground loop occur because the 0 reference voltage is the grounded wiper of the rotor. I can get the positive reference voltage from the Ken-Pro KR-500 for the A to D converter.
Now why didn't I think of that? Pretty simple.
Thanks a bunch.
John Kopala N7JK
----- Original Message ----- From: "i8cvs" [email protected] To: "John Kopala" [email protected]; "AMSAT-BB" [email protected] Sent: Sunday, December 03, 2006 12:11 PM Subject: Re: [amsat-bb] TrakBox Interface to HAM-IV Azimuth Rotor
Hi John, N7JK
I don't know if the control box of your CDE HAM-IV is similar to my Tailtwister T2X but they should be similar.
Since I am interested on this matter I have made some measurements to see if my T2X is a suitable rotator or not for a future automatic tracking system of my antennas.
The above rotator has the wiper of a 500 ohm potentiometer mechanically coupled to the inside of the aluminum hood using a cogged copper-berillium spring to get it rotate by 360° when the hood rotates.
Unfortunately going back and forth the mechanical coupling became too loose because of the aluminum wear and a big backlash between the actual position of the antennas and the indicated azimuth creates an error that make the above mentioned system less suitable for precise tracking purposes using this type of rotators.
From the electrical point of view the wiper of the potentiometer is grounded by the aluminum hood and cannot be insulated.
The negative terminal of milliamperometer ( I ) is connected to ground via a 5k calibrating pot. while the positive of it is connected to the positive of a power supply via a fixed 10 k resistor.
Terminal 3 of the 500 ohm potentiometer is connected to the positive and terminal 7 is connected to the negative of a stabilized voltage and both terminals 3 and 7 are insulated from the ground.
During operation when the wiper of the potentiometer is all the way to 3 the positive of the power supply is grounded and no current circulates in ( I )
When the wiper is all the way to 7 the negative of the power supply is grounded and the maximum positive voltage is available across ( I )
Connecting a voltmeter between the positive terminal 3 and the ground in 1 a positive voltage between 0 volt and about 13 volt is linearly available during 360° rotation.
If you need 5 volt for your Trakbox you should connect to terminal 3 a 5 k resistor in series to a 5k potentiometer in order to get 10 k across terminals 3 and 1 and get + 5 volts from the wiper and ground i.e. from the wiper and terminal 1
The system works but because of the above mentioned problem rotators like Yaesu and Ken-Pro are better for tracking purposes.
73" de
i8CVS Domenico
----- Original Message ----- From: "John Kopala" [email protected] To: [email protected] Sent: Sunday, December 03, 2006 12:11 AM Subject: [amsat-bb] TrakBox Interface to HAM-IV Azimuth Rotor
I am looking for a method to interface the TrakBox Azimuth Sense input to
the Azimuth indicator level from a CDE/Hy-Gain HAM-IV / CD-45-II Rotator.
It would seem that without a circuit to isolate the grounded return to the
control box meter the likelyhood of a ground loop occuring is high. The TrakBox expects an Azimuth indicator voltage to vary between 0 (its local DC ground level) and the positive reference voltage for the rotors.
I assume there are some TrakBox users using rotators other than the Yaesu
and Ken-Pro rotors who have encountered this problem and come up with a solution. There is no point in reinventing the wheel if there is already a suitable solution available that I can use.
I did receive a suggestion to use an op-amp to convert the level.
Any suggestions from TrakBox users?
John Kopala N7JK
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_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb