[amsat-bb] Re: Dish position pulse counter

David Barber david.barber at dbelectronics.co.uk
Fri Apr 25 03:29:19 PDT 2008

If pulse counting is used and since presumably the duration and expected
repetition of the pulse is known / can be calculated is it not possible to
discriminate between noise and a valid pulse?

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of i8cvs
Sent: 25 April 2008 11:11
To: Phil; AMSAT-BB
Subject: [amsat-bb] Re: Dish position pulse counter

----- Original Message -----
From: "Phil" <phillor at telstra.com>
To: <amsat-bb at amsat.org>
Sent: Friday, April 25, 2008 1:46 AM
Subject: [amsat-bb] Dish position pulse counter

> Thank you for reading this.
> I'm having second thoughts about the pulse counting scheme and I'm
> beginning to think that the tried and proven ten-turn pot method might
> be more fool proof.
> Regards,

> Phil.

Hi Phil

The ten-turn pot method is also not immune from inaccuracy when the
voltage across the pot is close to 0 volt i.e. when the rotator is turned
near to 0 degrees elevation.
In this condition the noise voltage picked up by the cable running from the
antenna to the control box can add with the low voltage available across the
Since you are able to write a program for a PIC a better method to get in
general a high pointing accuracy requested for a dish and expecially for a
big dish is to use different type of position sensors like the following:

Sequential encoders
Absolute encoders
Selsyn or Resolvers

With two inexpensive surplus selsyn for the azimuth and two selsyn
for the elevation on my dish I actually get a very accurate indication
of position on mechanical pointers but adding the Analog Device chip
AD2S80 I plan to write a program to get both precise digital indication
and automatic tracking with high accuracy

Look on google for the AD2S80 data sheet and for many technical
applications of it with syncro-resolvers.

Have fun

73" de

i8CVS Domenico

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