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

i8cvs domenico.i8cvs at tin.it
Sun Dec 3 11:11:27 PST 2006

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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