The receiving end of the station will normally consist of a “down converter” that brings the 2.4OSCAR 40 (AO40) The satellite pictured above, AO40 or OSCAR 40, is the latest Amateur Radio satellite to be placed in orbit. OSCAR is an acronym for "Orbiting Satellite Carrying Amateur Radio". AO40 carries numerous ham radio receivers and transmitters, which act as a "switchboard" in the sky.
Signals received by AO40 on one frequency are in turn transmitted back to earth on another frequency. This allows the ham (and anyone else listening) to hear his (or her) own signal and to talk to other hams around the world who can also "see" the satellite.
The satellite is in a highly eccentric orbit (egg shaped) that brings it as close to the earth as 1,000 Km, and as far away as 50,000 Km. This makes it seem to “hover” over one part of the earth for extended periods of many hours, enabling lengthy periods of communications before it drops below the horizon.
To use the satellite, you first must know where it is in the sky. Numerous software programs are available through the AMSAT (Amateur Satellite) organization to locate the satellites. You also need to be able to point your antenna at the satellite, which means that the antenna must rotate horizontally, as well as vertically.
There is a “ band plan ” for hams to refer to so that they know if they transmit on one frequency, they will be able to hear their signal on another specific frequency that is re-transmitted by the satellite.
The uplink frequencies are 435.550-435.800 MHz and 1269.250 to 1269.500 MHz. The
downlink passband is 2401.225-2401.475 MHz. The transponders are inverting, so a downward change in uplink frequency will result in an upward frequency shift in the downlink.The most common configuration for this bird is mode U/S, meaning that you transmit on 435
MHz (UHF), and receive on 2.4 Ghz (SHF). The satellite’s receivers are very sensitive compared to past amateur radio satellites. An uplink power of 10 - 100 watts on 440 MHz will suffice, using a crossed yagi antenna to provide circular polarization.AO40 (Phase 3D) Frequencies
Uplink
Digital (MHz) Analog (MHz) 15m None 21.210 - 21.250 12m None 24.920 - 24.960 2m 145.800 - 145.840 145.840 - 145.990 70cm 435.300 - 435.550 435.550 - 435.800 23cm (1) 1269.000 - 1269.250 1269.250 - 1269.500 23cm (2) 1268.075 - 1268.325 1268.325 - 1268.575 13cm (1) 2400.100 - 2400.350 2400.350 - 2400.600 13cm (2) 2446.200 - 2446.450 2446.450 - 2446.700 6cm 5668.300 - 5668.550 5668.550 - 5668.800 Downlink
Digital (MHz) Analog (MHz) 2m 145.955 - 145.990 145.805 - 145.955 70cm 435.900 - 436.200 435.475 - 435.725 13cm (1) 2400.650 - 2400.950 2400.225 - 2400.475 13cm (2) 2401.650 - 2401.950 2401.225 - 2401.475 3cm 10451.450 - 10451.750 10451.025 - 10451.275 1.5cm 24048.450 - 24048.750 24048.025 - 24048.275 Equipment Overview
Build Your Own 2.4 GHz Microwave Receive Antenna
GHz microwave signal down to something more “workable”, typically 144 MHz on the ham 2
meter band. The 2 meter signal is then fed into a standard 2 meter receiver.The 2.4 Ghz microwave receiving antenna is fairly very easy to assemble. My antenna is made from an old PrimeStar satellite TV dish. I scrounged the dish for free - PrimeStar is no longer in business and there are thousands of old dishes around the US that people are anxious to get rid of. A few simple modifications, and you're ready to go! Click here to see how to make your own .
Transmission modes include single sideband (voice), CW (morse code), and some unique digital modes. Additionally, hams can exchange slow scan television (SSTV) pictures on the satellite. FM or 100 percent duty cycle modes are NOT allowed on the satellite due to satellite power constraints.
Transmission signal strengths should be limited to no more than the signal strength of the
satellite’s general beacon. That means that if you transmit with TOO much power, it will tend to use more than your “share” of the satellite’s power, since the signal that would then be sent back to earth would mimic the strength of the signal received.To preclude one ham from monopolizing the power of the satellite, AO40 has a unique feature that will hopefully get the attention of the miscreant who doesn’t pay attention. A warning signal (siren) will be transmitted on the downlink frequency giving the offending operator the chance to reduce their power. If this fails, their signal will be eliminated by the satellite through the use of a “notch filter” until they reduce their power.
My uplink (transmitter) is an old Icom 475A that runs 10 watts of power. I also have an amplifier (RFConcepts 4-110) than can increase the power to around 100 watts, if necessary. The uplink antenna is a KLM 435-40 CX, a 20 element circularly polarized yagi antenna. Circular polarization is necessary due to the "Faraday" rotation effect on signals that otherwise causes fading.
Due to the orbit of the satellite, it is possible to talk to hams in virtually every country on the
planet. Since the earth moves (rotates) under the satellite, the footprint of the satellite changes constantly, bringing new countries into the picture on a regular basis.This allows the world’s ham radio operators to “share” the satellite, while enjoying dependable communication on a regular basis. See you on AO40?