[amsat-bb] Re: TrakBox Interface to HAM-IV Azimuth Rotor

[i8cvs]

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" <jkopala at gmail.com>
To: "AMSAT-BB" <amsat-bb at amsat.org>
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" <domenico.i8cvs at tin.it>
> To: "John Kopala" <jkopala at gmail.com>; "AMSAT-BB" <amsat-bb at amsat.org>
> 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" <jkopala at gmail.com>
>> To: <amsat-bb at amsat.org>
>> 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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>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>

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