ROTOR INDICATION BY PA3GJE ( PICTURES, SEE
SUB MENU, RED COLOURED
CHARACTERS )
Because of the need having a very good and accurate indication also useable
if working with a 'normal' ordinary rotator like a channel master, I was
finding out how to construct.
QUALIFICATIONS
INDICATION within 0.5 or even 0.1 degree ( 0.1
degree
without further modifications except changing the
voltage control regulator - INDICATION UNIT ) .....
LOW COST PROJECT only using a few components .....
The only ( simple but solid ) possibility is : mount the potentiometer axis
DIRECT ( WITHOUT plastic wheels etcetera between ) to the MAIN *
axis of the
rotator. Ofcourse the potentiometer has to be a hiQ one .....
* MAIN axis : the only part of the rotator with a 'zero tolerance' !
Also the indication ( LCD or LED ) unit must work accurate !
The tolerance of the electronic circuit must be at least :
0.1 % / 3.6 = 0.027 % .....
SOLUTION
1 THE ROTATOR ( a channel master ..... )
It is very easy to drill a hole into the main axis of a channel master
rotator.
After this you are able to draw a 'WIRE TAP'.
Because of the needed low tolerance I decided to use a hiQ flex cross
coupling system ( steel / teflon, in the early years often used in HF
radio's ). Via this component the potentiometer axis
is combined with / connected to the main axis of the channel master
rotator ( or another manufacture ). Because of the wire tap it is easy to do
( using some wire end ..... ).
During a test it appeared the combination of the potentiometer and the flex
cross coupling system was working very well, high accuracy, low
tolerance.
You can see the backlash of the rotator on the display, it shows a
true value, 0.8 degree in this case ( this channel master rotator not
often used ).
A lot of HAM rotators have possibilities replacing the potentiometer
systems.
The potentiometer is a 10 turn type of high quality.
Beware the linearity of it ! Many potentiometers do not reach
0.1 degree ( 0.027 % ) but for instance 1.0 degree ( 0.27 % ).
See the pictures : over the potentiometer house are soldered two 'stug' thick
wires in such a way it can not move in a wrong direction. Use a potentiometer
only needing small turning forces. If impossible : mounting the potentiometer
in a special frame is a much better solution.
2 INDICATION UNIT ( LED or LCD extern ..... )
By 'accident' ( hi ) I saw an article in Electron
( VERON ) november 2001 from PA0PLY on page 454 455 456.
When it is allright you will find these informations on :
http://www.qsl.net/pa0ply
I found the article interesting, however, because of the needed low
tolerance some little modifications became essential now.
I replaced the 7805 by a 3.3 VOLT type ( later on using a special high
precision adjustable voltage regulator LT 1086 CT 0.015
%, low drop ).
Between this regulator and ground I mounted an adjust potentiometer,
no using the diode on that place, see schedule article.
Because of the modification there was no need anymore in
adjusting the voltage on the rotator potentiometer 'loper', the
voltage divider on that location was no longer necessary and now we were
able to eliminate ( or maybe better - when using a DVM with a low input
resistance hi - to decrease ) the existing non linear voltage changings.
I removed the original adjust potentiometer with the two resistors 4k7
and 82k ( see schedule article ) or better : I did not use this
configuration.
In front of the now used voltage regulator I placed a cheap 12 VOLT device.
The system is a little bit more accurate now. The existing voltage drop
or rise ( see ADDITION, below ) is no longer there
.....
The modification causes no or less non linear voltage drop or rise. Ofcourse
you could add a DC opamp but here it is not necessary.
ADDITION ( about the voltage drop or rise ..... )
The voltage drop or rise exists because of the rotator turnings,
the potentiometer value is in or de
creasing, the resistance adaption
('match') between potentiometer and voltage divider is changing
: this
creates a non linear curve. The voltage to
be measured differs more and
more from the meaned, the original voltage. Ofcourse,
this is unwanted
now. Before modification
the existing maximal error of circa 0.25 %
( depending on the position of the adjust potentiometer too ) at the 360
degree point ( if calibrated at the 0 degree point,
the best to do is
always at the 180 degree point
) was resulting in a circa 0.9 degree error.
The more the antenna rotator direction point differs
from the
calibration point the more the error value.
After modification the voltage drop or rise has
been eliminated, no error
anymore.
The DVM ( with a high resistance ) measures the voltage on the rotator
potentiometer 'loper', no problem at all.
If the cable between rotator potentiometer and indication unit is not
too
long it is possible using a very cheap LCD or LED unit or multimeter without
zero adjust possibility, in most cases the reached tolerance is between
0.5 % - 1.0 % ..... ( not bad ).
However, if you need a 'zero adjust'
( for instance when the used
potentiometer does not reach zero ohm or using
very long cables ),
add a resistor and an adjust potentiometer to the circuit, setting the
needed voltage ( offset ! ) to the system.
It works very easy : to the meter min ( - ) input
we set a small
adjustable voltage via a voltage divider compiled by the resistor and the
adjust potentiometer. The input of the divider is connected to a point with
a fixed, stable voltage.
Advantages :
1 - It is no longer necessary the potentiometer value ( position ) starts at
zero ( 0 ).
2 - The cable to the rotator can be very long, as long as you want.
ADDED DUTCH TEXT
Stel, elke ader in de kabel heeft bij een bepaalde lengte een weerstand
van 100 OHM ( extreem voorbeeld ), vanaf de plus aansluiting ziet men
dan R1, kabel ader naar 'boven' ( 100 OHM ), P ( de rotor potentiometer,
onder te verdelen in P1 en P2 ) en R3, kabel ader naar 'beneden' ( 100 OHM ),
R2, de loper ader ( 100 OHM ), wordt in de berekeningen verwaarloosd omdat
deze GEEN kritisch onderdeel is in een spanningsdeler, de meter impedantie
is hoog.
Nu geldt :
000 graden stand : R3/(R1+P1+P2+R3).U=R3/(R1+P+R3).U
180 graden stand : (P2+R3)/(R1+P1+P2+R3).U=(P2+R3)/(R1+P+R3).U
360 graden stand : (P1+P2+R3)/(R1+P1+P2+R3).U=(P+R3)/(R1+P+R3).U
Voor een rotor potentiometer van 500 OHM geldt nu dat na enige berekeningen
zal blijken dat in plaats van 3.6 VOLT ( U ) juist circa 5.05 VOLT benodigd
is, je zou dus hier in dit theoretische voorbeeld ook de LT 1086 CT 5 VOLT
0.015 % spannings regelaar ( zie verder ) met een kleine instel
potentiometer kunnen toepassen.
Op de R2 aansluiting staat nu :
bij 000 graden : circa 0.72 VOLT
bij 180 graden : circa 2.52 VOLT
bij 360 graden : circa 4.32 VOLT
De benodigde zero adjust spanning ( toe te voegen aan
het systeem )
bedraagt nu circa 0.72 Volt. Uiteraard BLIJFT het systeem lineair
functioneren, dat ziet men ook in de results : tussen N1 en Z is
delta U 1.80 VOLT, tussen Z en N2 is delta U ook 1.80 VOLT.
Indien je de berekeningen uitvoert met niet afgeronde waarden dan zul
je zien dat het exact goed is.
Overigens een van de aardigheidjes bij het toevoegen van
een hulp spanning is
dat je met een correctie ( offset ! ) kunt werken. Staan je antennes
bijvoorbeeld 15 graden 'ernaast' dan kan je gemakkelijk deze 15 graden
bij of weg regelen. Natuurlijk moet een en ander in mechanische zin dan wel
in een zodanige toestand verkeren dat bij enige wind niet meteen opnieuw
een verdraaing optreedt, anders blijf je aan de gang.
Ook kan je 'rond het noorden' aan een kant ( bijvoorbeeld linksom ) een
negatieve aanduiding op het display verkrijgen ( bijvoorbeeld - 3.0 graden
indien je rotor in totaal 366 graden kan draaien, aan de andere kant,
rechtsom, vind je dan 363 graden, je hebt aan beide kanten een overlap
van 3 graden ), een sat tracker met een interface is nu niet nodig
ter verkrijging van de gewenste waarden op het display.
Indien er problemen zijn met de electronische eind stop ( zie fodtrack
en
yaesu modificaties ) kan je deze met de hierboven
beschreven hulpspanning
gemakkelijk elimineren.
CALIBRATION : FIRST adjust the divider potentiometer, till the LCD or LED
meter display shows zero VOLT ( rotator pointing zero degree ).
If the rotator has a turning possibility of more then 360 degree ( pe 375
degree ) you have ofcourse a ( minus ) - 15 adjust possibility ..... ( or
- 7.5 * ), also possible : offset adjust ( after
a storm or bad weather ).
* REMARK - 7.5 : rotator turns further around the
north ( 7.5 degree ), does
not stop at 0 degree ( rotator N1 pointing : 360 - 7.5 = 352.5
degree, rotator N2 pointing : 367.5 degree ).
Then adjust the ( 10 turn ) potentiometer of the 2.0 or 3.3 VOLT regulator (
if
using, see further, below ) to a 180 ( pe 1.8 or 0.18 VOLT ) or 360 ( pe 3.6
or 0.36 VOLT ) indication when the rotator pointing is 180 degree or 360 degree
( prefer 180 degree ). That's all. Thus a very cheap but also a very accurate
solution.
Ofcourse you understand : the values 1.8 and 3.6 VOLT belong to the use of
a 0.5 K and 0.18 and 0.36 VOLT to a 5 K ( 10 turn ) potentiometer.
I do not use the DVO ( when it is necessary, measuring very
secure the antenna pointing with a high precision DVM ..... ).
Now the combination is really able to measure with a 0.1 degree accuracy :
electronic tolerance needed : 0.027 % but with the LT
1086 CT regulator
( 0.015 % ) it will give a better result, you can be sure about a 0.1
degree accuracy result.
All depends on the used voltage regulators.
Using the LD 2517V33 ( 3.3 VOLT ) in combination
with an adjust potentiometer
delivers about 0.5 to 1 % tolerance.
If you have a very low tolerance type you better use in the combination
a 10 turn high precision type adjust potentiometer.
If using a 'normal' adjust potentiometer, calculate some extra resistors
'around' this potentiometer ( creating a certain voltage area ), adjustings
will be more secure and easy now hi. Use stabil METAL FILM resistors.
In case of a certain situation you could use the voltage regulator LT
1086-5 CT
5 VOLT 0.015 % .....
In most cases no adjust potentiometer can be placed between the regulator and
ground because of the fact we can not lower the voltage without making
concessions to the resistance ( becoming higher ! ), unless the needed voltage
U > 5 VOLT, see also above ( DUTCH TEXT ).
If the voltage U = or < 5 VOLT, it is necessary having an adjust possibility
in the LED or LCD meter.
A better solution is using the high precision adjustable low drop voltage
regulator LT 1086 CT 0.015
% ..... Use now a precision adjust
10 turn
potentiometer between the regulator and ground.
When distance between shack and rotator is very long ( see also above ) and
you do not use shielded cable then it could be necessary you place some extra
capacitors : now the indication unit will work without errors.
THE END ( hope not in a bad way ..... )
We know it is impossible to reach a channel master rotator controlled
pointing tolerance of 0.1 degree !
However, fact is : the point indication is very accurate, if
necessary you can construct it very easy, and it is guaranteed you will
reach a good tolerance ( indication unit ).
Costs : Because of no using DVO we found a cheap solution ( only the 10 turn
potentiometers and de special voltage regulator cost a little bit.
PS : The use of very low tolerances gives advantages in working satellites.
With accurate secure antenna systems ( good pointings, very low SWR,
perfect tuned antenna's etcetera ) you will reach very good results !
No longer important is the +/- 3 dB but the +/- 0.5 dB
beamwidth hi, see http://cebik.com,
W4RNL wrote very
interesting things about !
ADDITION ( PS )
I made some tests via a satellite ( AO-27, ideal because of the constant
output signal ) and used 50 mW into a ( fixed ! ) antenna, pointed very
accurate to the satellite. When the pointing became worser ( within
approximately 4 degree ) while the satellite was 'moving further' it was
IMPOSSIBLE to continue with the used actual low power .....
The transmitting antenna was not a very 'sharp' type.
Ofcourse I made several of these tests ( AOS situations ) to exclude
possible small polarization differences.
55 ( if necessary ! ) 73 leon ((-,O)) PA3GJE.