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Author Topic: Work a QRPppp... Satellite  (Read 384 times)

W9IQ

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Work a QRPppp... Satellite
« on: August 12, 2021, 04:18:02 PM »

The new AO-109 satellite has a problem with output power. The AMSAT team has also determined that the onboard telemetry is working, but the transmitter output is very low -- between 6 and 8 mW. AMSAT states:

Unfortunately, it seems that it requires a fairly “hefty” station to receive AO-109 telemetry. A normal end-mounted M2 LEO Pack, for example, is not enough. Everyone we have seen who has been successful has had a longer yagi, a preamp, and short coax. One person felt that the ability to reverse circular polarity also helped. Several SatNOGS stations have received a signal, but so far we have not been able to cleanly decode any of them.

It sounds like a nice opportunity for enterprising hams to put together a superior antenna system to help AMSAT obtain clean telemetry data. It is on UHF frequencies (435.750 MHz) so it is not unimaginable. Work the FSPL calculation to see what it would take...

Suggestion to AMSAT: Always publish a link budget calculation to make this simpler. "Hefty" is too technical of a term.

- Glenn W9IQ
« Last Edit: August 12, 2021, 04:32:03 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KD7RDZI2

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Re: Work a QRPppp... Satellite
« Reply #1 on: November 30, 2021, 12:05:38 PM »

The new AO-109 satellite has a problem with output power. The AMSAT team has also determined that the onboard telemetry is working, but the transmitter output is very low -- between 6 and 8 mW. AMSAT states:

Unfortunately, it seems that it requires a fairly “hefty” station to receive AO-109 telemetry. A normal end-mounted M2 LEO Pack, for example, is not enough. Everyone we have seen who has been successful has had a longer yagi, a preamp, and short coax. One person felt that the ability to reverse circular polarity also helped. Several SatNOGS stations have received a signal, but so far we have not been able to cleanly decode any of them.

It sounds like a nice opportunity for enterprising hams to put together a superior antenna system to help AMSAT obtain clean telemetry data. It is on UHF frequencies (435.750 MHz) so it is not unimaginable. Work the FSPL calculation to see what it would take...

Suggestion to AMSAT: Always publish a link budget calculation to make this simpler. "Hefty" is too technical of a term.

- Glenn W9IQ

I applied the wikipedia FSPL formula with some random thoughts. If the downlink were at 2m band it would  be more manageable. A 20 db gain antenna seems to me a bare minimum requirement other than preamp. Maybe an SDR with high decimation might help. About 20 years ago, at the beginning of the hobby as an SWL, I heard that telescopes at a large distance each other would be capable to add much more signal depending on the distance among the receiving stations  (the larger the better). I have no clue how that would be possible, but, if true it might be possibly experimented without using an EME setup.
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W9IQ

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Re: Work a QRPppp... Satellite
« Reply #2 on: November 30, 2021, 12:46:01 PM »

I applied the wikipedia FSPL formula with some random thoughts. If the downlink were at 2m band it would  be more manageable. A 20 db gain antenna seems to me a bare minimum requirement other than preamp. Maybe an SDR with high decimation might help. About 20 years ago, at the beginning of the hobby as an SWL, I heard that telescopes at a large distance each other would be capable to add much more signal depending on the distance among the receiving stations  (the larger the better). I have no clue how that would be possible, but, if true it might be possibly experimented without using an EME setup.

Congratulations for giving the formula a work out. It can be fun to do these types of estimates for various situations.

Since you worked with the formula, you probably discovered that you are missing a piece of information - the gain of the transmitting antenna. However, it we presume that it is 0 dBi as a conservative number and then apply a 500 km path distance, the FSPL is about 140 dB with a 0 dBi receive antenna.

If the receiver has a 0.5 μV sensitivity for solid reception, that is equivalent to about -113 dBm. The transmitter is putting out about 8 dBm of power. So we could tolerate about -113 dBm - 8 dBm or 121 dB of total signal loss. Since the path contributes 140 dB of loss, the receive antenna system would need to make up about 19 dB to come back to 121 dB of FSPL. The 19 dB includes all coax, etc. loss and we may want another 3 dB of budget for polarity mismatch. But a 22 dB antenna system is not out of the question.

- Glenn W9IQ

     
« Last Edit: November 30, 2021, 12:52:25 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.
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