DigiTwist

An Experimental, Simpler,

Lower Cost Satellite Tracker

Presented at BATC CAT17 by

G4EWJ

Some Current Options

• Yaesu G5500 AZ-EL rotator around £650

requires PC interface

• SPID RAS AZ-EL rotator around £900

includes PC interface

• Several homebrew systems with

stepper motors and feedback pots

E.g. G4KLB system using VK5DJ controller

Total system cost around £300

G4KLB System

The dish has 240v motors with gearboxes and position sensors

Photo:

G4KLB

A Possible Solution

Technomate

TM-2600M3

DigiTwist dual

Diseqc controller

Catapult Dish at Goonhilly

UPPER = arcsin (sin (AZ) * cos (EL)) LOWER = arccos (sin (EL) / cos (UPPER))

Photo:

G8GTZ

View from front Partial view from right side

Satellite

dish with

both

motors

centralised

Round tubing

Shaft angle of rotation = plus or minus 80 degrees.

Possible Configuration

Alsat Dark

Superior motor

TM-2600M3 motor

38mm square bar

Possible Configuration

TOP VIEW

Extension and

counterbalance

Possible Configuration

SIDE VIEW

TM-2600M3 motor

Joining Bar

Photo and CNC milling: M0DTS

Mounting Arrangement

Looking to the North

Orbitron Satellite Tracking Software

PC Interface Software

Visual

Basic

6

ISS Track

Orbitron

tracking software

Max ISS latitude

is 51.6 degrees

Advanced Torque Test Facility

Torque:

Alsat: 1.4 kgm

TM2600M3: 2.1 kgm

DigiTwist Advantages

• Rather cheaper than a G5500 (£650 vs £130)

• Uses the ‘Goto Angle’ Diseqc command

• 12/18v operation - no mains voltages

• No feedback pots or turns counters (see disadvantages)

• Rotate over elevate configuration like the Goonhilly Catapult dish

• 2 horizontal rotors at right-angles - no drama when the satellite goes

overhead

• Arduino Nano based positioner controller

• PC interface program accepts DDE position data from Orbitron

(other interfaces should be possible)

• Unknown if the positioners will last with loads and orientations they

weren’t designed for

• End mounted antennas only

• Antenna cannot be counterbalanced – it may be possible to

counterbalance at the rotor

• Only 2-3 degrees / second rotation speed - but this is usually fast

enough to track the ISS

• Low torque - about 2.1kgm - but this may be enough

• Basic rotor range is only +/- 80 degrees - operation near the horizon is

restricted (possible workarounds)

• No feedback – you don’t know where it is - only where you’ve told it to go

• Stops and starts when receiving a command, even if it was going the

correct way

DigiTwist Disadvantages

DiSEqC

• Digital Satellite Equipment Control - invented by Eutelsat

• Used to send data between satellite receivers and equipment such as

LNBs, switches and positioners

• Uses bursts of 22kHz tone superimposed on the 13/18v on the rx cable

• 22kHz tone was originally used to switch the local oscillator on LNBs

• Diseqc 2.x is bi-directional

• Diseqc 1.x is outgoing only

• Diseqc 1.2 allows positioner control with memory storage

• Diseqc 1.3 (also known as GotoX) allows angular control of the rotor

• USALS, invented by STAB, is used with GotoX and knowledge of your

LAT / LONG to position to any satellite using its longitude

Diseqc Protocol

18v 650mv

pk-pk

E0 31 6E Ex xx CLOCKWISE

E0 31 6E Dx xx ANTI-CW

22kHz

RT5047A

LNB Voltage Regulator:

Surface mount 1.27mm pin

spacing with underside

ground pad

Finding Local South

• Compass

• Google Earth

• Shadow of mounting pole

• Shadow of a southerly rope attached to the pole

Local noon time varies from day to day

At the Greenwich Meridian (zero degrees longitude):

9 September 2017 11:57:17 UTC

31 July 2017 12:06:23

1 September 2017 11:59:57

2 November 2017 11:43:31

https://www.esrl.noaa.gov/gmd/grad/solcalc/

Lightweight Dishes

Construction

and photo:

GM8OTI

Based on a

design from

the RSGB

International

Microwave

Handbook

http://www.marwynandjohn.org.uk/GM8OTI/proj2mdishantenna/proj2mDishAntenna.html

Lightweight Dishes

Construction

and photo:

GM8OTI

Based on a

design from

the RSGB

International

Microwave

Handbook

http://www.marwynandjohn.org.uk/GM8OTI/proj2mdishantenna/proj2mDishAntenna.html

DigiTwist

Presented at CAT17 by G4EWJ