RotorDRV TSR Add-On to "Flip" Antennas Over

Must Be Art > Software > FlipAnts


Most antenna azimuth rotators have a mechanical stop at some bearing, typically due North or South. The antenna cannot be rotated through the stop. It must instead go all the way around, which takes a while (typically 60 seconds). One way of avoiding this problem is to move the elevation rotor "up" over the top, past the zenith and back down to the required elevation. This changes the azimuth by 180 degrees, which effectively moves the mechanical stop to the opposite side. That's what this package does.

FlipDRV is a DOS TSR (terminate-and-stay-resident) program for use with antenna rotator drivers compatible with the programming interface defined by the Kansas City Tracker (KCT). This interface allows application programs, especially satellite tracking programs such as InstantTrack, to control a two-axis antenna rotator without needing to know any details of the hardware. The hardware driver, referred to as RotorDRV, is installed as a TSR program, and accepts commands through software interrupts. FlipDRV installs as a second TSR on top of RotorDRV, and monitors the commands being sent from the application program to RotorDRV. When it sees a command to set or get the current azimuth and elevation, it modifies these values as described above and passes them through.

FlipAnts is a very simple DOS command-line program to control FlipDRV. It can turn "flipping" on or off, or query the current state.

System Requirements

To run FlipDRV, any environment capable of running an MS-DOS TSR program is required. This certainly includes all versions of MS-DOS beyond 2.0. This program will also work under all versions of Windows or OS/2, but the underlying RotorDRV may or may not work satisfactorily in such environments.



There's a missing component to make this automatic: a program to determine in advance whether a given satellite pass calls for the antennas to be "flipped" or normal. For now, this determination must be made manually. You can do this with InstantTrack by bringing up the map screen with groundtrack enabled. If the groundtrack passes South of your location, and your mechanical stop is at South, for example, you need to enable "flipping".

It is always possible to avoid the mechanical stop for any LEO satellite pass. However, a satellite with a high eliptical orbit can sometimes pass both North and South of you during the same pass.

Current Status

Stable. No current development plans. The current released version of FlipDRV is unnumbered. The current released version of FlipAnts is 0.6. Both were released in March 1993.


Known Bugs



FlipAnts and FlipDRV may be distributed freely (unmodified) and may be used freely for non-commercial purposes only. Modified versions must be marked as such.

Source Code

Source code in assembly language for Microsoft MASM 5.1 is included for FlipDRV, and source code in C for Microsoft C 6.00A for FlipAnts. A single makefile for Microsoft MAKE builds both.


FlipAnts.TXT - user manual (plain text, 9K)

DRVSVC.TXT - programmer's specification for the KCT software interface

KCT-passthru - programmer's specification for KCT TSR extensions


FlipAnts (zip file, 19K)

Copyright 2002 Paul Williamson. Comments to kb5mu@amsat.org