Improved readout and speed
control for the KR400 and 600 rotators
Dave Robinson WW2R, G4FRE
Introduction
For
the past 6 years in Texas, I have
been using a Kenpro KR600 rotator to rotate my antenna arrays for up to 7
bands. With the addition recently of a 10 and 24GHz
dish it was realised that better pointing accuracy and the facility to slow the
speed of rotation was needed. Discussions with Dave
Powis G4HUP pointed me to a design in DUBUS which I had
previously missed, mainly because it was written in German and has never been
translated. It was entitled “Einfach Drehzahlsteueurung fur rotoren”, by
Michael Kuhne, DB6NT and was published in DUBUS 2/99
pages 77-80. The DB6NT design is intended to be incorporated into the existing rotator
controller box. Upon review, it was seen that few of the controllers components
remained in use; transformer, left and right switches and the 100uF non
polarised capacitor. It was decided to build a stand alone unit, leaving the
original controller untouched for future resale.
Design
The
circuit is shown in Figure 1. It is shown wired for 110V AC; however the
components were chosen to easily accommodate changing the supply voltage to
240V AC.
A 5
volt regulated supply is fed across the feedback potentiometer in the rotator.
The voltage produced by the wiper of the potentiometer is used, suitably scaled
to give 0 to 360 readout on a 200mV Full scale LCD meter unit.
To
control the speed of rotation of the rotator, the AC supply voltage to the
primary of the transformer, which drives the rotator motor is pulsed using a
solid state AC relay (RL1). The frequency (VR1) and width (VR2)
of the pulses are adjustable and can be used to set the speed to suit
particular needs. Two independent supplies, one 9V, one 5V are needed due to
the operational requirements of the LCD; the LCD cannot share its ground with
the circuit it is measuring. The push button switches chosen have integral
lamp/LED holders. The illumination method employed is derived from the one
employed in the KR600 controller. The LEDs in the “left”/”right” switches (SW2,
SW3) are normally illuminated, but when the
rotator is activated their corresponding LED is extinguished. The LED in the
full speed/slow speed switch (SW4) is illuminated in the “full speed” position
and flashes when the unit is in the slower speed position, as do the left and right
switches.
Construction
The
original board obtained from DB6NT needed
physical modification to use components readily available in the USA.
Therefore a “USA”
PCB was devised, the track layout is shown in Figure 2
and the component overlay in Figure 3. This PCB suits the components given in
Table 1. If an equivalent has to be used for the solid state relay, RL1, It must
be one with low drive requirements. The specified one requires under 2mA of
drive current which IC3 can supply. Other, non buffered solid state relays can
require up to 30mA of drive and will not work. All the components were mounted
in a 8x6x3.5” Bud box. The rotator is connected to the controller
through a 6 pole waterproof connector on the back panel, a type which I standardised on for all my rotators
20 years
ago. Numerous RF decoupling capacitors and RFC were added to stop the adverse effects of RF,
especially when operating on 50MHz
Calibration
Firstly
determine accurately the direction of true North. Make sure SW1 is in the “full
speed” position. With the Left (anticlockwise)
switch turn the rotator until it points true North. Using VR3 set the LCD to
read 000. With the Right (clockwise) switch turn the rotator 360 degrees until
it points again exactly true North. Set VR4 to read 360 on the LCD display.
These settings are interactive so this process will need to be repeated a
couple of times to get exactly the correct LCD readings. VR1 and VR2 are adjusted
to give the required slow rotation speed with SW1 depressed
Conclusions
The
unit was finished just in time for the ARRL 2002 September VHF contest (OK to
be exact it was calibrated the morning OF the contest). The number of times that the beam heading was
calculated, the antenna pointed at that direction and peaking the antenna on a
signal resulted in no improvement in signal strength, even on 10GHz was
amazing. Having the ability to point the antenna in exactly the same direction
12 hours apart, to have a second attempt to work the same station was also a
revelation. It was well worth the effort in constructing the unit.
Table 1 Component Listing
R1 68R
R2 27k
R3 680k
R4, R5, R6 2k2
1W
R7
For 110V operation 2R2
5W, for 240V operation 4R7 5W
VR1 200k
preset Bourns type 3329H (DK 3329H-204)
VR2 10k preset Bourns type 3329H
(DK 3329H-103)
VR3 10k 10Turn Bourns type 3299Y (DK 3299Y-103)
VR4 100R
10Turn Bourns type 3299Y (DK 3299Y-100)
C1, C2 470uF
25V electrolytic
C3, C4 10uF 25V Tantalum
C5, C6 1uf
25V Tantalum
C7 100uf
60V NON POLARISED
C8 3u3
ceramic
IC1 7809
IC2 7805
IC3 74HC00
D1 1N4518
(Shottky)
D2, D3 100PIV
1A minature bridge rectifier (DK DB102DI)
D4, D5, D6 IN4001
V1 120V
Varistor
LCD 3.5
digit 200mV FSD 5V supply (C&C PM-128
from JDR Microdevices)
TR1 Toroidal
transformer. Primary 2 x 120V Secondary 2 x 12V 1.1A (DK TE62072)
TR2 PCB
Transformer. Primary 2 x 120V Secondary 2 x 10V 0.3A (DK MT2111)
SW1 DPDT
latching, integral LED holder (NKK LB26SKW01), Red Lens (NKK AT419C)
SW2, 3 DPDT
momentary, integral LED holder (NKK LB25SKW01) Green Lens (NKK AT419F)
SW4
DPDT Mains rated.
LED1, 2 Minature
Green LED
LED 3 Minature Red LED
RL1
Solid
state relay CMOS drive (MP120D4, Newark 91F5736) (see text)
(DK = Digikey; www.digikey.com)
Figure
1:Circuit Diagram
Figure 2:PCB
layout
Figure 3:
Component Layout
LAST MODIFIED 18 January 2006