By now, I think it’s clear that I’ve got a bit of an interest in electronics and most things RF related. As a result, I spend a bit of time trying to grab signals of various sorts, be it regular line-of-sight terrestrial, or by shortwave/HF, or by amateur or broadcast satellite.
Part of that includes chasing feeds on satellites, which is why I’ve spent a bit and amassed a collection of Ku dishes to optimize the signal collected from each satellite, a pair of TBS6925 Crazyscan-capable professional blind-scan satellite cards, many DiSEqC switches, reels of RG6 and compression connectors, assorted satellite finders and a box full of Sharp LNBs. Through some self-education online, and practical hands-on experience, I taught myself how to construct, align, install dishes and crimp my own RG6 cables and design a “switched fabric” DiSEqC setup for more versatility.
Too bad there’s no space for any C-band dishes where I am right now, so my focus has been mostly on Ku, which is where most of the satellite news gathering and feeds tend to be. The number of satellites is generally limited, and once you start scouring them, you get used to their band plan and you know where to look for the “fun”, and where the unusual signals might be.
Back in 2011, Optus announced their tenth satellite, provisionally named Optus 10, to serve Australia. This was exciting to me, because it should mean that I get another satellite to listen to. The satellite would be delivered in 2013, and was slated to be launched that same year. Unfortunately, that was delayed by about a year to 12th September 2014. Since the news of the successful launch, everything has been quiet on the Optus 10 front, with no real news or service carriage. We know it’s parked at 160 degrees East, but that’s about it.
This is probably not unexpected, as it takes some time for the satellite operator to verify the health and performance of the satellite and do some in-orbit qualification testing before commissioning the satellite to full service.
To help me along with my quest, I purchased and set-up a new 75cm Ku-band dish. I wanted to purchase a 90cm dish, but the seller did not have a complete set, and an 85cm was not available either, so I had to compromise. The dish is equipped with a Sharp dual 10700Mhz LNB, and is on a “portable” camping tripod for easy positioning and aiming. I’ve also enlisted the Tektronix RSA306 Real-time Spectrum Analyzer which I won via element14 RoadTest earlier to help me identify the signals, along with the TBS 6925 professional satellite tuner card.
The Satellite Landscape
Because the vast majority of my friends who will read this probably have little to no understanding (no offense!) of the Ku-band satellite situation in Sydney, Australia, I decided to write this section to give some background of the satellite arrangement and the difficulties behind hunting Optus 10. Of course, because I’m writing this after the experiment has been completed, some things might seem obvious to the reader now, but only because I’ve learnt through the process and conveyed that knowledge to you ahead of time.
The hand-drawn illustration above is a summary of the satellite positions in Sydney, illustrating the Clarke belt of geostationary satellites with the notable satellites serving Australia in the Ku band scribbled on, along with their elevations.
In Sydney, Optus D2 is almost directly north of you, with Optus C1/D3 (Foxtel/VAST) satellites being just slightly further east, then Optus D1 (SBS/ABC) satellites being a little further east, and so on. Because of careful stationkeeping maneuvers, the satellites are “held” within a tight tolerance of their orbital slots, unless the satellite is in inclined operation. Inclined satellites operate with a figure-eight style wobbling above and below the Clarke belt, but the equatorial crossing is maintained at the orbital slot.
Our interest, Optus 10, currently resides in the 160 degrees East slot, according to the very helpful calculations made from two-line elements by satellite-calculations.com. This is where things gets a little complicated.
The 160 degrees East slot is a bit special, because it’s the slot where Optus B3 (a close-to-life-expired satellite) normally operates in an inclined mode. Optus B3 is not known to carry regular broadcasting traffic, as the inclined operation requires two-axis tracking dishes to get a usable signal around the clock. In fact, it’s not likely to carry any significant traffic, but its presence will make determining the presence of Optus 10 signals more complicated since we will have to work out if the signals from the slot are received from Optus B3 or Optus 10.
In general, satellites serving a given area should be spaced about 4 degrees apart, hence why the Optus series of satellites are placed in slots 152 degrees East, 156 degrees East, 160 degrees East and 164 degrees East. But the 164 degrees East slot is unique, because at 166 degrees East, a competing Intelsat-19 is blasting away sending strong Ku band signals to Australia. Because of the proximity, it is very likely that received signals may contain significant components from Intelsat-19.
As a result, a zoomed-in view of the situation looks a bit like the diagram above. The 75cm dish has a -3dB beam width of 2.1 degrees, which is wider than the two slots – so it will be receiving Intelsat-19 at ~3dB down when (perfectly) pointed at Optus 10’s slot. The Optus B3 satellite has an inclination of about 6 degrees at the present time (thanks to satellite-calculations.com, which also let me know the equator crossing times), meaning that it will swing far out of the dish’s field of view in the extremes.
If I had a 90cm dish, the situation would improve slightly, as the -3dB beamwidth of it will be about 1.9 degrees. This means I will get less of Intelsat-19’s signals “creeping” in, although it wouldn’t eliminate it altogether.
I’ll have three signals to contend with, and a bit of work to do to tease them apart.
Fortunately, there’s another factor which is added to the mix. Satellite signals are generally sent with two orthogonal polarities (horizontal and vertical in linear polarization systems, or left-hand and right-hand circular polarization in circular polarization systems) to allow for frequency re-use. Due to the position of the satellite and the receiving dish, a skew factor is introduced to make sure the horizontal and vertical components “line up” with the waves from the satellite to maximise the signal.
For most satellites, the satellite will emit the signal with 0 degrees of skew offset, meaning that for a satellite directly overhead, the LNB would be set to 0 degrees. With this, if all satellites in the Clarke belt followed this convention, horizon-to-horizon satellite motors which “tilt” the dish will automatically “align” the LNB’s skew for each of the satellites along the belt.
Optus seems to be the exception to this, with their satellites being configured for a 45 degree skew offset. This means a satellite directly overhead has a 45 degree skew, rather than a zero degree skew. This arrangement is problematic for people who want to use horizon-to-horizon motors to target non-Optus satellites with 0-degree skew offset as the LNB would be performing very poorly as the antennas would not be aligned correctly polarity-wise.
But in this situation, this set-up can be of a benefit. As Intelsat-19 is configured with a 0-degree skew offset, and Optus B3 is configured with a 45-degree skew offset, an LNB aligned for Optus B3’s skew would see any interference from Intelsat-19 as a “mix” of horizontal and vertical polarity signals, rather than direct interference. This “mixture” could help “whiten” the noise so it appears as a degradation of signal-to-noise ratio and not result in erroneous capture-or-decode of the signal on the adjacent satellite. Where only one polarity is used (as in the predecessor to Intelsat-19, Intelsat-8), then the interfering signal’s level is “halved” on both polarities for more even performance (rather than full interference on the same polarity, and ~25-30dB down on the orthogonal polarity).
I’m sorry if this is a bit complicated, but that’s a quick summary of the landscape and some of the factors contributing to difficulties in hunting for Optus 10.
Doing the Homework
Before going “hunting”, it pays to do some homework. Aligning a dish to a satellite that’s in service is fairly simple, as there is a lot of energy in the transponder carriers (driven to saturation) carrying the TV and data services, making using basic satellite finders viable. I have a slightly more complex satellite finder, which is basically based around a DVB-S set-top-box, battery and LCD in a portable form factor, but this relies on knowing at least one DVB-S carrier’s parameters to lock onto.
How does one go about hunting a satellite in a slot where there is no known reliable services operating? We’ll answer this later, but first, it pays to do a little homework.
When it comes to satellites, one of the first things they will have is a beacon. This is a transmitter which sends a pre-defined signal to help you identify the satellite and can be used to help you spatially aim the dish towards the satellite. The beacon signal can also carry telemetry and command data, which is basically to do with the health of the spacecraft, for the operators. Otherwise, the beacon signal could be for attenuation estimation as part of a feedback system. Regardless, a beacon can be identified with a spectrum analyzer and can serve to be a positive identification mechanism.
After a bit of digging, I was able to assemble a list of beacons used by the Optus fleet to date, excluding Optus 10. This includes historical satellites which are no longer in service, for completeness. The data for Optus A and B series satellites comes from their Satellite Network Designers’ Guide, whereas the data for Optus C1 comes from the payload information, as does the data for Optus D series satellites. The information in the documents are primarily intended for customers who intend on designing satellite systems to directly uplink to the satellites, and many competing satellite providers do not provide this information openly to the public.
Each beacon is designated common, telemetry, or uplink power control, which designates its type and whether to expect modulation (i.e. none for UPC beacon). The frequency and polarity are provided, where left-hand circular polarized (LHCP) beacons can be received in both linear polarities at a lower power level. The calculated corresponding intermediate-frequency for a “wideband” 10700Mhz LNB is also calculated to give us a place to “aim” our spectrum analyzer, which is listening on the IF from the LNB.
By looking at the beacon data, we can already make some generalizations.
- Satellites prior to Optus D3 all transmitted their telemetry beacons in such a way that it would be received in the horizontal polarity.
- Optus D3 is the first to change to vertical polarity for the telemetry beacons.
- Satellites prior to the Optus D-series all transmitted their beacons in the upper end of the Ku band (near 12750Mhz).
- The Optus D-series satellites all transmit their beacons below the regular broadcast Ku band (under 12250Mhz) which does not waste potential revenue-gaining bandwidth, except for Optus D1’s UPC beacon.
- Optus D2 and D3’s UPC beacon are near 12200Mhz, about 50Mhz below the regular Ku broadcast band edge.
- Uplink power control beacons can always be received in either polarity.
- Optus D-series satellites have a telemetry beacon separation of 2Mhz.
Unfortunately, as the specifications of Optus 10 are not available yet, we will have to use these generalizations to guide our identification. It is believed that Optus 10 follows similar design rules to the D-series satellites.
If you look along the IF column, you will notice that the frequencies of some of the beacons can be quite high. I wasn’t going to chance it with using an RTL-SDR as a result, because the front end would be operating a long way outside its intended range, and that would only further complicate this experiment. That’s where the Tektronix RSA306 becomes my best friend.
Aiming the Dish and Refining its Aim
The first step is to aim the dish. For those with a horizon-to-horizon dish motor, and a good alignment with the Clarke belt, it is as simple as driving the dish to the location. But getting good alignment isn’t always easy, and such a solution is more complex and expensive.
I already know that aligning to Intelsat-19 would be easy, because of its strong signal, so I went there straight away. Knowing the beamwidth of the dish, I would then turn the dish towards the west and raise its elevation slightly until the carriers from Intelsat-19 weaken to the point of unlocking. That would have my dish nearly pointed at the right spot.
As it turns out, this strategy worked somewhat, and blindscan found a new, strong signal which wasn’t present on Intelsat-19. The signal was 12389Mhz, horizontal polarity, 7200kS/s, DVB-S QPSK, FEC 1/2. The service was named GWN News Backhaul, and the NIT claims the provider to be Ericsson. A clear MPEG2 video channel was provided, but was a constant black-screen with silent MPEG1 audio.
I tweaked the dish until the signal to noise was the highest that it would go, and tilting it in any direction would reduce it. Normally, that would complete the dish alignment and I can go back to analysis.
Whoops! That’s not quite it!
I realized my mistake pretty quickly as the signal disappeared that same night. It is a signal from Optus B3.
However, it proved to be its own opportunity, as keeping a monitor on the signal allowed me to verify that it was indeed, likely to originate from the inclined Optus B3 satellite due to the way the signal strength swings up and down twice a day.
Of course, there could be one more possibility – it could be a customer uplinking with a two-axis tracking system to an inclined satellite that’s not there, causing the repeated signal to swing in strength. I will need to be more systematic to untangle the signals.
A Systematic Methodology
Knowing that the intuitive straightforward way wasn’t going to yield the results I wanted, I had to be more systematic and thus, over two days, I began the real experiment in earnest.
Identifying Optus 10’s Orbital Slot
As I have identified an Optus B3 satellite carrier, that would help me steer the dish to the right place to have the dish pointed at the slot properly. In order to do that, I would have to know when Optus B3 crossed the Clarke belt, and maximise the signal at that time. Thankfully, with the detailed data from satellite-calculations.com, it seems Optus B3 has a regular crossing every 12 hours at 3:30am and 3:30pm (or thereabouts).
I waited until 3:30pm and aligned the dish. This allowed me to take a spectrum with Crazyscan.
Waiting until later in the day at 9:30pm, when Optus B3 should be out of view, the spectrum is subtly different – notice the loss of two main carriers near 12350-12400Mhz.
I attempted to identify the carriers without Optus B3 in view. Many of the carriers would not lock at all, either because of insufficient SNR, or maybe non-DVB-S/S2 transmission mode.
Locks were achieved at:
- 12366Mhz, vertical, 13300kS/s, DVB-S QPSK, FEC 2/3
- 12446Mhz, vertical, 13300kS/s, DVB-S QPSK, FEC 2/3
- 12597Mhz, horizontal, 30000kS/s, VCM
- 12606Mhz, vertical, 30000kS/s, VCM
All of the locked carriers above did not yield any video-data. The transport stream carriers did not yield proper transport streams, with continuous continuity errors suggesting maybe a low-level modulation test-pattern is being transmitted. The two VCM carriers appeared to be IP-DVB services.
These services are likely to be coming from Optus 10 due to their non-time varying nature.
Additionally, when Optus B3 was in view, attempts to lock the other carriers were made.
Locks were achieved at:
- 12361Mhz, horizontal, 16276kS/s, DVB-S QPSK, FEC 1/2
- 12389Mhz, horizontal, 7200kS/s, DVB-S QPSK, FEC 1/2
The first one also seems to be full of continuity errors and doesn’t have any sane data, whereas the latter presents itself as a MPEG-2 video service named GWN News Backhaul. The time varying nature of these two carriers implies the operation of an inclined satellite, but does not confirm it, as it could be the result of a “tracking” uplink dish pointing in and out of Optus 10’s slot. To confirm Optus B3’s operation will take some more work.
As a result, we were able to determine that test carriers are on the air, and knowing these parameters may allow you to easily re-align the dish to the present 164 degrees East slot Optus 10 is at.
One of the problems with just looking at the locked signals is that there is no high certainty that it is not a result of interference from Intelsat-19 which would be just in the field of view. As a result, a scan was done on Intelsat-19 and attempts to lock the frequencies above were made.
It is clear that there might be a bit of spill-over of Optus 10 into the Intelsat-19 dish, but the locks at the frequencies show different carriers, so the locks above are not a result of interference from Intelsat-19. The interference will not be due to any other satellite adjacent either, as the next adjacent broadcast satellite to Australia has a 4-degree separation (and I know its characteristics already).
This provides more positive identification that it is Optus 10, as the signals are not due to Intelsat-19.
To do more low-level identification of signals requires the power of the RSA306. With both Optus 10 and Optus B3 in view, here are the spectrum scans (covering 12200-12800Mhz, i.e. more than the broadcast 12250-12750Mhz band).
Optus 10 + Optus B3 Horizontal Polarity
Optus 10 Horizontal Polarity
Intelsat-19 Horizontal Polarity
Looking at the horizontal polarity scan, we can see similar results to the Crazyscan results above. Some narrow-band or even CW style transmissions seem to be contributed by Optus B3. It is clear that the interference from Intelsat-19 is no where near as severe as I would have expected, as the pattern of signals from Intelsat-19 doesn’t really show up in the Optus 10/Optus 10 + Optus B3 traces.
Optus 10 + Optus B3 Vertical Polarity
Optus 10 Vertical Polarity
Intelsat-19 Vertical Polarity
It seems clear the interference, again, is not apparent. Optus B3 seems to make only a few small narrow/CW carrier contributions to the trace. However, by looking at the traces, we have some beacon candidates to follow up on.
Looking at the spectrum traces above, we can already see the beacons to some extent. The first beacon to note is the UPC beacon – this appears to be the spike right near 12200Mhz which is present on both horizontal polarities. Measurement of this gave me an IF frequency of approximately 1501.61046Mhz. Unfortunately, due to the ~2Mhz tolerance of the L.O. in the LNB, an accurate measurement of the frequency is not really possible. However, it would correspond to a frequency of about 12201.61046Mhz. This seems to be in the same line as the Optus D2 and D3 UPC beacon allocations. If I were to guess, maybe it is really 12202.10Mhz.
The telemetry beacons appear to be vertically polarized, just like the Optus D3 satellite. The 2Mhz beacon separation is also apparent, with the measured IF frequencies of 1533.009017 and 1535.009017Mhz, corresponding to 12233.009017Mhz and 12235.009017Mhz. The location and separation, as well as the format of the beacon being FM-subcarrier, is consistent with what I’ve seen on Optus D2.
Switching over to horizontal polarity, the signal was almost silent. I adjusted the skew of the LNB until the horizontal polarity went silent, and that confirmed the skew offset of 45 degrees, which indicates these beacons are not likely to be from Intelsat-19.
For further verification, snooping around on my dish pointed at Intelsat-19 to check it wasn’t from Intelsat-19, actually revealed Intelsat-19’s beacons, which are not published openly.
These beacons are also FM subcarrier type, however, their beacon spacing of 3Mhz is inconsistent with all Optus satellites. The weak signal strength is received on both polarities, indicating circular polarization, also inconsistent with Optus satellites. Finally, the second telemetry beacon features two FM subcarriers, which I haven’t seen on Optus satellites. Therefore, these beacons belong to Intelsat-19.
The I.F. frequencies (very roughly) seem to be 1551.965679Mhz and 1554.971929Mhz for telemetry beacons, and 1555.478179Mhz for the UPC beacon. This corresponds to a transmission frequency of 12251.965679Mhz, 12254.971929Mhz and 12255.478179Mhz, which are all inside the bottom of the Ku broadcast band, which is inconsistent with the design of later Optus D-series satellites.
For fun, lets see what the Optus 10 beacons look like from the Intelsat-19 dish …
Optus 10 beacons from Intelsat-19 dish tuned to Horizontal Polarity
Optus 10 beacons from Intelsat-19 dish tuned to Vertical Polarity
As you can see, the effect of 45 degree skew means that the signal levels are reduced somewhat and the interference is “spread” across both polarities.
This leaves one more challenge – identify Optus B3’s beacons when it is in view. Unfortunately, this was easier said than done, as despite the information we had in the designer’s guide, no beacon was heard.
Upper Ku-band Beacon Area, Horizontal Polarity
Upper Ku-band Beacon Area, Vertical Polarity
Multiple attempts were made to try and hear the beacon, but nothing was ever heard. Did this mean Optus B3 is turned off and ready for graveyarding?
Verifying Optus B3’s Operational Status
How can we work out of Optus B3 is still on the air if we can’t hear its beacon? Logically thinking, we can use the inclined orbit is a characteristic to kill two birds with one stone.
If we wait until the satellite is at least 4 degrees away from the Clarke belt and aim the dish at the satellite, then we should be able to hear the transmissions from Optus B3 with no ambiguity. A properly-stationed satellite, such as Optus 10, would not be heard with the dish aimed this far away from the belt.
Knowing already that we have an Optus B3 transponder to aid in alignment, I waited until evening when the satellite has ventured far away enough to isolate it from the rest. I then optimized the pointing of the dish to the GWN News Backhaul transponder.
The result of this was successful, isolating only the B3 services, which show clearly against a “quiet” background.
A look at the satellite on its own allows for unambiguous looking around for beacons.
As expected, the satellite doesn’t seem to be carrying anything on vertical polarity, although a few spikes seem to show up. The horizontal polarity has only a few services, but a few of them are spikes as well. The low-end near 12250Mhz on horizontal has a very unusual set of multiple CW tones turning on and off slowly, nearly randomly. I suppose this shows the low demand for inclined services in this geographical region.
The problem with the upper spikes is that they are so low in amplitude that they could be CW spikes from RF-dependent/IF-dependent spurs in the spectrum analyzer. They are also significantly below the top end (12750Mhz) of the band and are unlikely the beacons because the expected power at Sydney is greater than that of the D-series which normally show up very clearly.
This leaves a spike that shows up below the 12250Mhz band. Zooming in seems to reveal a pair of unmodulated carriers, spaced 1Mhz, which could be a beacon of sorts. They are horizontal polarity only, and the 1Mhz spacing corresponds to the spacing between the B-common and B-UPC beacons, but I suspect this is all just a coincidence as neither feature any modulation which is expected.
Regardless, I am confident that Optus B3 is indeed operational despite not being able to hear the beacon at the expected frequency. This may be due to failure of the beacon transmitter, spacecraft reconfiguration or use of alternate beacons, as Optus B3 also carries a 30Ghz Ka beacon, and L-band payloads.
With that, I am fairly confident that I have indeed identified Optus 10 and it is putting out some signals, which appear to be for testing at this stage. We have also identified Optus B3, despite the lack of expected beacons, which remains operational in an inclined mode at this time.
Despite the difficult environment, I am satisfied that I have been able to “separate” the composite signal’s components through systematic measurements. I have high confidence that I have achieved successful reception of Optus 10. The measurements seem to show that Optus 10 is carrying traffic, although it is not of video broadcasts, and many of the carriers are not blind-scan lockable. The ones that are seem to have many TEI errors and do not produce a sensible transport stream output, which may imply the use of “test pattern” signals for testing. This seems likely based on the spacing and repetitive patterns of some of the carriers.
Beacons were identified, which seem to follow the patterns expected of an Optus satellite. Verification of the skew was undertaken, and a confirmation that the signal is best tuned with a 45 degree skew offset, which is a characteristic Optus satellite trait.
Further to this, I was able to use the existing Intelsat-19 reception system to verify that the identified carriers were not a result of spill-over from the nearby Intelsat-19’s transmissions and were unique.
These transmissions were validated as likely to originate from Optus 10, as they remain consistent, as opposed to the time-varying signal component which comes from the inclined Optus B3. Furthermore, alignment of the dish to one of the extreme points of the inclined Optus B3 satellite’s movements allowed us to exclude any signals from adjacent satellites entirely, which clearly identified only a small number of carriers which originate from Optus B3. Therefore, the remainder must originate from Optus 10.
The lack of beacons from Optus B3 seems to be a surprise, although it may be due to reconfiguration of the satellite itself, with an L-band payload available and a Ka-band beacon available as well which will not suffer any potential interference, it may have been deliberately commanded off.
The role of Optus 10 is still not fully known, but the press releases makes references to Foxtel, which makes us suspect it will eventually be “floated over” to the “Australian-Hotbird” (in Optus’ words) slot at 156 degrees East, likely to take over from Optus C1, launched 2003 and due to (nominally) expire in 2018 (based on the 15 year design life).
This might mean that Optus C1 will eventually be floated over to the 164 degrees East slot to hold it, as Optus B3’s 13 year nominal life expired in 2007, and its 5 year inclined life extension would have been up by 2012. There, Optus C1 may resume “inclined” services in the 164 degrees East slot, which is a relatively “disadvantaged” slot due to the close proximity to Intelsat-19’s 166 degrees East slot which actively serves strong direct-to-home Ku broadcasts to Australia.
The fact that Optus B3 is still going beyond its expected lifetime seems to be a combination of great luck, solid engineering on behalf of Hughes Space Systems and great operational care by Optus. It is not unprecedented, as Optus A3 was sold to SES after completing its service with Optus, and was only shut down in April 2008 after 21 years on a satellite with a design life of 10 years and 5 years inclined life extension.
We will see how everything plays out, but I suspect that Optus 10 was more of a capacity-maintenance launch, to ensure continuity of service, rather than adding genuine capacity to the air. That is, unless, it turns up a surprise in the transponder arrangement, which seems unlikely. Perhaps it has the ability to go down to the lower Ku band rather than just operate in the 12250-12750Mhz “regular” slot, but seeing as D1 is already providing the 11700-12250Mhz slot in both polarities, it would have to go below this, and receivers will need to use a Universal (dual L.O.) LNB rather than the 10700Mhz “wideband” ones currently used (which displaced the regular 11300Mhz regular LNBs).