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USNA APRS/PSK31 CubeSats Offer Something Different

05/28/2015

The APRS/PSK31-equipped US Naval Academy satellites appear to be operating, with one exception, according to Bob Bruninga, WB4APR. The CubeSats were launched on May 20 from Cape Canaveral. The launch included a pair of 1.5U CubeSats — the PSAT APRS/PSK31 satellite and BRICsat, a propulsion/PSK31 satellite — as well as a 3U CubeSat, USS Langley (Unix Space Server Langley). The launch also included The Planetary Society’s LightSail-1.

 

PSAT, a student satellite project named in honor of USNA alum Bradford Parkinson, of GPS fame, contains an APRS transponder for relaying remote telemetry, sensor, and user data from remote users and Amateur Radio environmental experiments or other data sources back to Amateur Radio experimenters via a global network of Internet-linked ground stations.

Brno University transponders on PSAT and BRICsat support multi-user PSK31 text messaging (28.120 MHz uplink/435.350 MHz FM downlink). The PSK31 multi-user FDMA transponder experiment on PSAT and BRICsat allows text messaging among up to 30 modest ground stations simultaneously, Bruninga said. The BRICsat and PSAT PSK31 transponders operate on the same frequency, although one has PSK telemetry on 315 Hz, the other on 365 Hz.

Bruninga said the PSAT telemetry on 145.825 MHz (1200 baud AX.25) is working okay, but the digipeater is off at present, since the PSK31 transponder is the primary mission. The APRS downlink page has been capturing PSAT telemetry.

Bruninga said BRICsat’s telemetry has been heard, but has been cycling off, due to low power. He said the BRICsat PSK31 downlink has been heard, but only barely. “BRICsat seems to have some kind of problem,” he told ARRL. The USS Langley spacecraft has not been heard yet, he said.

BRICsat transmits 9600 baud telemetry on 437.975 MHz. The USS Langley satellite transmits 9600 baud telemetry on 437.475 MHz.

The LightSail-1 packet 9600 baud (FSK) AX.25 downlink is on 437.435 MHz. The Planetary Society’s Jason Davis is asking radio amateurs to e-mail him any data they collect from LightSail, including any screenshots.

Bruninga has invited APRS radio amateurs worldwide to tune into the packet downlinks and upload IGate packets into the global APRS-IS system, so they will appear on the APRS downlink page, and also to try out the “exciting, new full-duplex PSK31 way of multi-user communication.”

PSAT is one of five APRS-networked Amateur Radio satellites that will be in orbit during 2015, and all will appear on the live APRS downlink page. The others include PCsat-1, in orbit since 2001, QIKcom-1, set to launch in September, QIKcom-2, set to launch in December, and the ARISS packet radio system on board the International Space Station since 2007.

Bruninga said that receiving the PSAT and BRICsat 435.350 MHz FM downlink is as simple as placing your PC microphone (on a computer equipped with PSK31 decoding software) next to the speaker of your FM satellite UHF receiver and “just watching the waterfall.”

“What you see is exactly what everyone else sees,” he said in a posting to the AMSAT reflector. “There is no Doppler added to the tones, due to your station’s position relative to the satellite. But you do have to retune at least three times during the pass (+5 kHz, 0, –5 kHz) to stay in the FM passband.”

Bruninga said user uplinks will shift in the waterfall, according to each user’s position relative to the satellite. “The shift can be as low as 1 Hz per second to as high as 6 Hz per second,” he explained. “This is because the uplink is on 10 meters where the Doppler rate is only 1/15th of what it would be on UHF.”

The telemetry channel at 315 Hz (PSAT) or 365 Hz (BRICsat) is fixed with no Doppler, since it is generated onboard into the FM downlink, Bruninga said. He notes that the UHF downlink signal is only 300 mW, and a beam antenna would be required to hear the signal.

Bruninga advised that those transmitting to the satellites use nothing more than a dipole or quarter-wave vertical, and no more than 25 W output power. He reminded prospective users that this is cross-band, full-duplex, “so you can see yourself in the downlink just like everyone else can see you. Act accordingly. And of course, do not transmit if you cannot see the waterfall.” 



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