Phase I of the Viestikallio SCR-584 pedestal upgrade




The F1EHN/OH2AUE/OH1JJC SCR-584 tracking box

- our OH2Z SCR-584 pedestal mounted 4 meter dish system (62k) is in dire need of a control upgrade

- this fantastic dish is manufactured in Kuorevesi, serial number 001, surface accuracy +- 2 mm

- originally this was imported into Finland by professor Martti Tiuri for the HUT Radio Laboratory in 1967

- a photograph of the dish just after installation, Tekniikan Maailma (106k), 8/1967 - huomaa teksti ;-)

- this dish at OH2Z can be used for Amateur Radio Astronomy, EME and tropo contacts and also SETI

- the main upgrade, Phase II, will also be ready for installation soon

- OH1JJC and myself decided to rapidly deploy a temporary F1EHN type tracking system

- this temporary Phase I upgrade will use the original main axis 60 Hz Selsyns on the SCR-584 pedestal

- these Selsyns will now be excited at 400 Hz to output an accurate three phase position indication

- D/A conversion to 16 bit resolution is by Data Device Corporation SDC-501 synchro to digital converters

- as the initial 400 Hz source, a very Fletcheresque amplitude stabilized Wien bridge oscillator prototype (72k) is used

- both azimuth and elevation Selsyns need a 90 V RMS excitation signal (58k)

- this is achieved by amplifying the 400 Hz sine wave with a 5 W TDA1011 audio amplifier

- feeding a 15 V/230 V toroidan transformer, ample isolated drive is available with low distortion

- the measured distortion @ 90 V RMS, 400 Hz is < 0.3 % (60k) with even 0.015 % THD possible at the cost of stability

- here is a plot (38k) of the amplified 400 Hz synchro drive signal (taken with a Yokogawa DL1540L)

- actual antenna motional control is via an F1EHN interface card using relays

- the upgraded DC motors run off a separate 24 V, 4 A power supply

- are we happy to get rid of the Amplidynes and vacuum valve amplifier systems !

- a full rack of valve equipment and two Amplidynes can now be replaced with a 2U high 19" rack unit

- advantages are: silence, low power consumption, less real estate, less odor and last but not least: computer tracking :-)

- when Phase II is ready to roll, this temporary Phase I unit will be installed on my 3 m dish (70k)

- this box will now allow antenna tracking of any arbitrary radio target with ease

- SCR-584 repeatability accuracy is 0.09 degrees, readout resolution is now 0.01 degrees, accuracy +- 0.02 degrees

- DC motor PWM speed control can easily be added with solid state FET switching

- 12 V power consumption is 700 mA for the 400 Hz exciter and 1050 mA for the LED display

Some photos of the new temporary Phase I controller:

All that is needed for operation is 230 V AC for the box, 24 V for the motors and a tracking PC !

First installation tests on 21-22.02.2004 weekend (photos OH1JJC & OH2AUE):

Second installation tests on 05-07.03.2004 weekend(photos by OH2KFH & OH2KFX):

X band receiver lab work during 16.04 - 18.04.2004 (photos by OH1JJC & OH2AUE):

ESA Rosetta spacecraft reception tests during 04.05 - 06.05.2004 - photos by OH4KPN (69k) and OH1JJC, (92k):

Miscellaneous documents:


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Updated 15.10.2005