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RE: Fodtrack readout



Hi John

> I've constructed a FODTRACK that works well, but I
> noticed that: the "starting point" (or terminating) of bearing-rotator is
> straight to SOUTH (180°), probably that is the program's default.
> Is it possible to change that by 180°, in order
> to terminate the rotor in the opposite direction? (terminate to NORTH).

You'll see in the FODTRACK.CFG file the following entry:

;Azimuth rotator end stop position. 0 for south, 1 for north.
;This is the position where your rotator runs against a limit switch or
;mechanical stop. It is NOT the parking position.
0
;

Set this value to '1'.

> I wondering, because if you have a Digital readout(DVM) into the Shack,
> the problem with SOUTH "starting-point" is unsolved till now for me.
> For example,if the reference voltage is 0 V on DVM, the antenna looking
> to SOUTH (180°).
> If the ref.voltage is 0.180 V, the antenna looking to NORTH (360°) !
> If the ref.voltage is 0.359 V, the antenna looking to 179° SOUTH !
> Exactly the opposite that the DIGITAL readout needs.
>
> (In contrast, if the starting point is straight to NORTH, the "bearing"
> is equal to DVM indication, ie 0V=0°, 0.90V=90°, 0.180V=180° etc).

Fodtrack expects the CCW-most position to be 0V and the CW-most position to
be 5V. Normally calibration to this 5V value is performed by adjusting the
rotator's feedback output. ISTR that I altered the 5V value to a different
voltage by changing the two 39k resistors around U2C and U2D to other
values - one of the two FODTRACKs I have built replaces the resistors with
multiturn pots here. If the maximum voltage is too low (like the 0.359V you
suggest), accuracy will suffer due to noise on the power supply lines. It
would be better to have 3.60V representing a CW-most position.

There is no simple way to change the 0V offset that I've come up with, but
this has never caused me any practical concern in this design.

Alternatively for DVM output you could always use a high impedance potential
divider instead on the Az/El returns from the rotator, say using a 100k
multiturn pot to set the maximum. This assumes your DVM has a nice high
impedance input of course.

73, Howard G6LVB

-----Original Message-----
From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]On
Behalf Of Electronic Dep
Sent: 12 April 2005 10:05
To: amsat-bb@amsat.org
Subject: [amsat-bb] Fodtrack readout


Hi Amsats,

I've constructed a FODTRACK that works well, but I
noticed that: the "starting point" (or terminating) of bearing-rotator is
straight to SOUTH (180°), probably that is the program's default.
Is it possible to change that by 180°, in order
to terminate the rotor in the opposite direction? (terminate to NORTH).

I wondering, because if you have a Digital readout(DVM) into the Shack,
the problem with SOUTH "starting-point" is unsolved till now for me.
For example,if the reference voltage is 0 V on DVM, the antenna looking
to SOUTH (180°).
If the ref.voltage is 0.180 V, the antenna looking to NORTH (360°) !
If the ref.voltage is 0.359 V, the antenna looking to 179° SOUTH !
Exactly the opposite that the DIGITAL readout needs.

(In contrast, if the starting point is straight to NORTH, the "bearing"
is equal to DVM indication, ie 0V=0°, 0.90V=90°, 0.180V=180° etc).

Any suggestion is welcome.

Regards

John Smith
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
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