C-band Sats – Part 7: 142E-150E (?) Unidentified/Mystery Satellites

The last post ended on a semi mystery at around 140°E which I believed to be Express AM5. A look at the Lyngsat satellite chart shows that there aren’t any known C-band satellites between 138°E Telstar 18 and 166°E Intelsat 19 that serve Australia. As a result, I was expecting to see a gap in the belt with no satellites to mention as their signals would be too weak to hear outside the intended footprint.

However, instead of that, my spectrum analyzer seemed to show a few spots where it was clear that a satellite was being heard. Without any lockable known DVB services, they’re hard to positively identify based on signals alone. I didn’t have any precision inclinometer either, so I couldn’t even determine exactly what elevation or azimuth I was pointed at, but I would guess that all the satellites mentioned in this post lie between 142°E and 150°E.

Mystery 1: Inclined (?) satellite near 142°E?

This first mystery was based on aligning to Telstar 18 first, and then shifting elevation positive until something new was seen. It’s different from what was seen in the suspected Express AM5 sighting, instead only showing very few narrow carriers. Unfortunately, it seems that whatever the source of the signal was, it disappeared while I was trying to analyze it. I suspect this might point to an inclined orbit satellite “drifting” in and out of view, but I don’t know of any of this particular band in this area of the sky. As a result, I’d say this one might remain a mystery.

Mystery 2: 142°E MySat 1 (?) or 146°E AsiaSat 3S (?)

Nudging the dish ever-so-slightly to try and regain the previous signal, I instead came across this pair of spectra. Most of the services are in the vertical polarity in the regular C-band area with some in the low-end on the horizontal. I suspect this is probably MySat 1, or otherwise known as Apstar 9. Only one DVB occasional-use service is known but I couldn’t lock any. Otherwise, it could be AsiaSat 3S, serving its last few years in inclined orbit operation.

In the horizontal at 3819.36Mhz, we can see some familiar satellite modem carriers.

Likewise, on the vertical 3862Mhz, we can see both single and double-width slotted data.

The most obvious beacon appears to be at 4200.193125Mhz in the horizontal polarity, AM type with narrow subcarriers at 28khz and 48khz. This could be consistent with one of AsiaSat 3S’s known beacon frequencies at 4198.50 H / 4199.625 H.

These two CW carriers are spaced 500khz apart, and look like potential beacons. Frequencies are approximately 3851.47958Mhz and 3850.7958Mhz. Alternatively, they could be analyzer images?

Especially since I observed the same spacing, mirror image power relation crossing over actual data services, I suspect this may be a result of imperfections in the analysis equipment rather than actual transmitted signal.

This signal on the vertical at 4011.986865Mhz seems like a beacon … but looking closer …

… I’m not too sure. The outer carrier is 290khz, but unmodulated and could well just be intermodulation products.

There are more of these harmonically related carriers as well. So I have absolutely no idea what this satellite is … but it’s definitely a satellite.

Mystery 3: 146°E AsiaSat 3S (?) or 147.8°E Measat 2 (?)

This one has an even higher elevation than the one before, so it could be AsiaSat 3S if the previous one was not, or it could be Measat 2. None of the services will lock on a DVB card though.

This operates in the standard C-band in both polarities, with many thin data modem carriers as well.

In the horizontal, the narrow data carriers seem to be continuous transmission with pretty sharp rolloff.

The wide vertical carrier is an extremely wide (>40Mhz) carrier with repetitive patterns. This suggests this satellite has 54Mhz or 72Mhz transponders (!!) consistent with the two hypothesized satellites. What is not consistent is the horizontal polarity transmission as Measat 2 only transmits on vertical polarity, but this may be the horizontal polarity from an adjacent slot as it looks very similar to that above.

I probably didn’t quite get the skew right, but the only beacon I could spot seemed to be a CW beacon at 4200.526274Mhz in the vertical. This seems consistent with one of the listed 4198,125 V / 41199,125 V (sic, I suspect they mean 4199.125V). Given Measat 2 is multi-band, the Ku probably carries the telemetry.

Mystery 4: 150°E BRIsat (?)/146°E AsiaSat 3S (?)/145.1°E Express A4 (?)

This appears to be an odd satellite, primarily used for banking transactions across Indonesia, but with no known DVB services. Or maybe it’s the real AsiaSat 3S? It’s a bit hard to know exactly where the dish is pointing …

Nothing locked even though I tried, so maybe this one’s an ACM/VCM service.

One key characteristic is that everything seems to be horizontal polarity, with a quiet vertical polarity.

In the horizontal, lots of narrow continuous data transmission services.

In the vertical, this strange signal was spotted – kind of reminds me of spread-spectrum clocking.

Looking at the high end of the band, it seems we have two beacons in the horizontal and one in the vertical. These are approximately:

  • 4200.714299Mhz (H, unmodulated)
  • 4200.582799Mhz (V, unmodulated)
  • 4199.589299Mhz (H, modulated)

This doesn’t seem consistent with the expected 4193.5 and 4195.5Mhz beacons. As a result, it’s probably not BRIsat. But it does have a 1.125Mhz space between the two horizontal beacons, matching the expected spacing for Asiasat 3S. Maybe it’s just the spill-over?

There is a stray CW carrier which may also be a beacon at 3801.106727Mhz in the vertical. Maybe I’ve got a dielectric plate left inside the LNB because somehow this appears consistent with a single-polarity satellite 145.1°E Express A4, which only transmits LHCP with a beacon at 3800Mhz LHCP.

Conclusion

It’s quite surprising to me that in a patch of sky where I didn’t expect to hear any signals has provided quite a few unexpected signals. Identifying the source is a bit of a challenge given the limited publicly available information, and the fact that some of these signals appear/disappear with time due to inclined orbit operations. I’m still quite happy that I’ve fulfilled my curiosity in wanting to know whether we could hear anything from satellites whose footprint does not target us directly. There’s still more to come though … one more mystery too.

About lui_gough

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