Fall 2006 Issue
Working AO-51 Mode L/S, Eagle Update, CubeSat Launch a Failure, HITSAT Launched Successfully
By Keith Pugh, W5IU
This time in satellite news we will cover
working AO-51 Mode L/S, the latest developments of the Eagle satellite,
the failure of the massive CubeSat launch, the demise of SuitSat-1, and
the successful launch of HITSAT. We’ll start out with AO-51 mode L/S.
AO-51 recently completed another successful round of mode L/S operation. This mode, more than any other used so far, points out the necessity for computer control of radios and antennas for successful operation.
A number of sessions of mode V/S have proven to be very popular on AO-51, and many operators have trained themselves to correct for ±53 kHz of Doppler on the S-band downlink while ignoring the ±3 kHz on the V-band uplink. Of course, one must not forget antenna control at the same time, and again, the V-band uplink can usually be ignored by using a simple antenna and a little more power. With normal manual dexterity, one can often adapt to all of this and have many successful contacts on mode V/S.
Now back to mode L/S. The ±28 kHz of Doppler on the uplink cannot be ignored, and a directive antenna is usually required on the L-band uplink as well as on the S-band downlink. To summarize, one is now faced with ±53 kHz of Doppler on the downlink, ±28 kHz on the uplink, and control of two directive antennas, not to mention holding a microphone, talking, and taking notes for the log. I ran out of hands to do all of this a while back! Remember, this is still FM on AO-51, and Doppler tracking need not be nearly as precise as it would be for SSB or CW.
Fortunately, a computer can be trained to do the tracking tasks while freeing the operator to do the communications tasks. Actually, the computer can also be trained to do the communications tasks for the digital modes. Unfortunately, in addition to the computer, one must also have the proper computer software and hardware interfaces to the radios and rotators.
A number of good tracking programs for the computer are available. Personally, I find SatPC32 from AMSAT fills the bill nicely on all fronts. I am able to run it in my old notebook computer and control the antennas through a USB port and the Lab Jack and Lab Jack Piggyback interfaces to my G-5500 rotor while controlling the uplink and downlink frequencies through a serial port to my FT-847 radio. Of course, this also requires the obvious up and down converters between the radio(s) and the antennas. Depending on the intermediate frequencies of the converters, alternate radios may be used. Variations on this scheme may be required for your hardware due to different interfaces, etc. SatPC32 contains the drivers for a number of popular rotor and radio interfaces.
Calibration of the setup becomes important and is accomplished by changing constants in the tracking software to compensate for pointing errors and the frequency calibration of your radio/converter configuration. Since your down converter, and possibly your up converter, is usually located at the antenna, temperature drift becomes very important and at least seasonal changes to the compensation must be made. You may even want to consider temperature control of the remotely located equipment.
Don’t let all of this intimidate you. It sounds complicated, but it is really quite straightforward, even though a little challenging. Remember: “If you’re not careful, you learn something every day.”
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