Posts by s-band

Quote from strannik

But it would be wrong to consider them as "signals" ...

Interferometry has nothing to do with it, IMHO

Sorry, I was referring to the 4 other signals, which carry the same data stream as the main one. If you remove the differential Doppler and take into account that the frequencies were measured over a period of about 30 minutes, they seem to be at multiples of 500kHz from the main carrier.

RE: Tianwen 1 (Mars mission)

Unfortunately we don't have any information from the operators so you may be right on the cause of the 65kHz sub-carrier's odd harmonics.

Here are today's plots with TW1 at about 5Mkm from Earth.

strannik Hi, The odd harmonics of the down-link sub-carrier are most likely to be due to it being modulated as a square wave. I always seem to miss the times when the up-link loop-back spectrum is present. That's seen as the close in lines on Paul's plot. I think that Spectravue is automatically highlighting the highest 4 peaks for that snapshot, Paul will correct me if I'm wrong. The overall spectrum of Tianwen is a little messy. It's hard to know if some of the signals are intentional, possibly for long base-line interferometry.

r00t.cz has posted details of the modulation and decoding here

8407.108 = 21.4MHz

-123.6dBm 142kBd MCD3 on DSS54, Madrid

Nice signal from 282.7Mkm, -156dBm on a 1.2m dish .

-119.7dBm on DSS55, Madrid, 600kBd

-127.7dBm on DSS65, Madrid at 96.3Mkm (34m dish)

-156dBm on the 1.2m dish

Now at about 3 million km and still very strong, -112.6dBm using a 1.2m dish.

See Daniel Estévez TCM1 blog post about the first correction manoeuvre.

Now at 1.3 million km I can no longer see the modulation. The amplitude and frequency variations are still there.

It was a struggle to find it today. If the Doppler were faster or the frequency not exactly know there would have been no chance.

At about 4.3 million km.

Mars 2020 launched on 30th July. It's frequency, without Doppler compensation, is 8415.000MHz, RHCP.

There are both amplitude and frequency variations as it spins. r00t.cz and Daniel Estévez have been decoding the telemetry.

Signal a few hours after launch:

Amplitude variations in time and frequency domains:

Thanks to the efforts of amateur optical and radio observers, the ephemeris data is now very accurate. JPL have added it to the Horizons database with this identification: Tianwen-1 (spacecraft) [-9901491]

Links to latest information:

Daniel Estévez Twitter

Achim Vollhardt Twitter

r00t.cz Twitter

TW1 has 2 pairs of sidebands which have the same structure and modulation as the main signal. It's hard to believe they are spurii, more investigation needed. Today the levels, on a 1.2m dish, were:

8407.914 -137dBm

8411.747 -124.6dBm

8430.907 -111dBm

8450.007 -124.6dBm

8453.897 - 139.2dBm

The main signal, on 8430.907 (+/- Doppler). Here are the 4 sidebands:

21.4MHz = 8410.537MHz
-126dBm DSS65 Madrid 33kBd
88.8 Mkm

Daniel Estévez has posted tracking data here Thanks to everyone involved in this project.

It appears to have increased in signal by about 8dB in the last couple of days. I need to re-calibrate as the power increase reported was about 5 dB yesterday.

The channel power plots show the total power in a couple of bandwidths. The noise level was -113.33dBm in 1.25MHz and -122.24dBm in 165kHz.

Getting weak now it is at 2.7 million km. I will lose it soon if it's not switched to the high gain antenna.
21.4 = 8402.67411MHz

-127.3dBm (total power) at Madrid on DSS65
-162dBm (carrier only) here on a 1.2m dish

Tianwen switched to the high gain antenna at around 00:30 UTC this morning. It is now very strong at -115.7dBm at the feed of the 1.2m dish.

Edgar, DF2MZ https://twitter.com/df2mz, has collated and processed tracking data to produce very good celestial co-ordinates. Tianwen was at about 1.2 million km from Earth this morning according to calculations by Daniel Estévez https://twitter.com/ea4gpz. Thanks to everyone involved in this.

8430.907 = 21.4 MHz, wide spectrum inverted, narrow non-inverted

Not strong enough to see the sidebands now. Thanks to DF2MZ for all the work on the tracking co-ordinates.

8430.907 = 21.4 MHz, wide spectrum inverted, narrow non-inverted

The first plot has averaging set to 64. The slope is due to the IF response of the RX.

Quote

Original von Feedsat
Thanks a lot s-band for your contributions in this frequency range .

There are many "Mars mission" @ the moment ?!

You're welcome. This one was a difficult one as the Chinese did not release much information. Thanks to uhf-satcom and others on #hearsat IRC channel for their help.

https://mars.nasa.gov/mars2020/ carrying Perseverance Rover is due to be launched on 30th July.

Not seen for a while but back to a good signal now it's at 103 million km
8420.72MHz = 21.4MHz wide spectrum inverted, narrow non-inverted

1,130,000km
Wide spectrum limited due to 10kHz IF filter

Stronger now it's only 103 million km away
21.4MHz = 8439.64MHz wide spectrum inverted, narrow spectrum correct sense.
3MBd