QO-100 beacons power

In the QO-100 (Es’hail 2) narrow band transponder, the recommendation for the adjustment of your downlink signal power is not to be stronger than the beacon. This was also the recommended usage of the old AO-40. Since the transponder has two beacons marking the transponder edges: a CW beacon marking the lower edge and a 400baud BPSK beacon marking the upper edge, there has been some debate on Twitter about which beacon does this recommendation refer to and what does “stronger” mean.

Of course, more formally, signal strength means power, which is a well defined physical concept, so there should be no argument about what does power mean. However, there are two different power measurements used for RF: average power and peak envelope power. I will assume that the recommendation refers to average power, not to peak envelope power. This makes more sense from the point of view of the power budget of the satellite amplifier (The total average power it needs to deliver is just the sum of the average powers of the signals of all the users, while the behaviour of the peak envelope power is much more complicated).

Also, I think that using peak envelope power for this restriction would be a very strict requirement on high PAPR signals. Note that the PAPR of CW is 0dB and the PAPR of BPSK is between 2 and 3dB, depending on the pulse shaping, so these are rather low PAPRs. For comparison, a moderately compressed SSB voice signal has a PAPR of 6dB.

In my opinion, the main problem with these discussions about “signal strength” is that many people are trying to judge power by looking at their waterfall or spectrum display and seeing what signal looks “higher”. This kind of measurement is not any good, because it doesn’t take signal bandwidth into account, depends on the FFT size, the window function, etc. It doesn’t help that many popular SDR software don’t have a good signal meter displaying the average power of the signal tuned in the passband.

In any case, I was curious about whether the power of the two beacons is the same and whether there is any interesting change over time. I have made a GNU Radio flowgraph that measures the power of each of the two beacons and of the transponder noise, and saves them to a file for later analysis.

Decoding the QO-100 beacon with gr-satellites

On February 14, the Amateur transponders on Es’hail 2 (which now has the AMSAT designation QO-100) were inaugurated. Since then, two beacons are being transmitted by the groundstation in Doha (Qatar) through the narrowband transponder. These beacons mark the edges of the transponder.

The lower beacon is CW, while the upper beacon is a 400baud BPSK beacon that uses the same format as the uncoded beacon of AO-40. I have already talked about the AO-40 uncoded beacon in an older post, including the technical details.

Based on my AO-40 decoder in gr-satellites, I have made a decoder for the QO-100 beacon. Patrick Dohmen DL4PD has been kind enough to write some instructions about how to use the old ao40_uncoded decoder with the BATC WebSDR. I recommend that you use the new qo100 decoder. You just have substitute ao40_uncoded by qo100 in Patrick’s instructions

As additional hints, I can say that for the best decoding, the beacon must be centred at 1.5kHz into the SSB passband. The centre of the signal is easy to spot because there is a null at the centre, due to the use of Manchester encoding. Frequency stability is somewhat important with this decoder, so if your LNB drifts too much you may run into problems.

The SNR of the beacon over the transponder noise floor is rather high, so you should achieve a clean decoding unless you are using a very small station and you have the transponder noise way below your receiver noise floor.

The following data is being currently transmitted on the beacon (the timestamps and packet numbers are added by gr-satellites):

2019-02-19 21:56:27
Packet number 68
UPT: 3d 0h 29m CMD: 91 LEI_REQ: 0 LEI_ACT: 0
TEMP: 56 C VOLTAGES: 1.0 1.8 1.0 1.0 1.8 1.5 1.3 0.0 0.5 Volts
TFL: 0 TFE: 0 TFH: 0 HFF: 0 HTH: 0 HR: 0

2019-02-19 21:56:53
Packet number 69
EXPERIMENTAL MODE. Measurements and tests being conducted,
experimental transponder use OK, but expect ground station tests
Watch this space and www.amsat-dl.org for further announcements

Es’hail 2 stationed in 26ºE

If you’ve been following my posts about Es’hail 2, you’ll know that shortly after launch Es’hail 2 was stationed in a test slot at 24ºE. It remained in this slot until December 29, when it started to move to its operational slot at 26ºE. As of January 2, Es’hail is now stationed at 26ºE (25.8ºE, according to the TLEs).

The new GEO orbit at 26ºE is much more perfect than the orbit it had at 24ºE. This is to be expected for an operational orbit. Since December 30, I’ve been recording Doppler data of the satellite moving to its operational slot, and I have found some interesting effects of orbital dynamics in the data. This post is an account of these.

Es’hail 2 differential Doppler measurements

Since I published my Es’hail 2 Doppler measurement experiments, Jean Marc Momple 3B8DU has become interested in performing the same kind of measurements. The good thing about having several stations measuring Doppler simultaneously is that you can perform differential measurements, by subtracting the measurements done at each station. This eliminates all errors due to transmitter drift, since the drift is the same at both stations.

Of course, differential measurements need to be done with distant stations, to ensure different geometry that produces different Doppler curves in each station. Otherwise, the two stations see very similar Doppler curves, and subtracting yields nothing.

The good thing is that Jean Marc is in Mauritius, which, if you look at the map, is on the other side of the satellite compared to my station. The satellite is at 0ºN, 24ºE, my station is at 41ºN, 4ºW, and Jean Marc’s is at 20ºS, 58ºE. This provides a very good geometry for differential measurements.

Some days ago, Jean Marc sent me the measurements he had done on December 22, 23 and 24. This post contains an analysis of these measurements and the measurements I took over the same period, as well as some geometric analysis of Doppler.

It would be interesting if other people in different geographic locations join us and also perform measurements. As I’ll explain below, a station in Eastern Europe or South Africa would complement the measurements done from Spain and Mauritius well. If you want to join the fun, note a couple of things first: The Doppler is very small, around 1ppb (or 10Hz). Therefore, you need to have everything locked to a GPS reference, not only your LNB. Also, the change in Doppler is very slow. The Doppler looks like a sinusoidal curve with a period of one day. To obtain meaningful results, continuous measurements need to be done over a long period. At least 12 hours, and preferably a couple days.

One month of Es’hail 2 Doppler data

In a previous post I talked about my Doppler measurements of the Es’hail 2 10706MHz beacon. I’ve now been measuring the Doppler for almost a month and this is a follow-up post with the results. This experiment is a continuation of the previous post, so the measurement setup is as described there.

It is worthy to note that, besides the usual satellite movement in its geostationary orbit, which causes the small Doppler seen here, and the station-keeping manoeuvres done sometimes, another interesting thing has happened during the measurement period.

On 2018-12-13 at 8:00 UTC, the antenna where the 10706MHz beacon is transmitted was changed. Before this, it was transmitted on a RHCP beam with global coverage. After the change, the signal was vertically polarized and the coverage was regional. Getting a good coverage map of this beam is tricky, but according to reports I have received from several stations, the signal was as strong as usual in Spain, the UK and some parts of Italy, but very weak or inexistent in Central Europe, Brazil and Mauritius. It is suspected that the beam used was designed to cover the MENA (Middle East and North Africa) region, and that Spain and the UK fell on a sidelobe of the radiation pattern.

At some point on 2018-12-19, the beacon was back on the RCHP global beam, and it has remained like this until now.

The figure below shows my raw Doppler measurements, in parts-per-billion offset from the nominal 10706MHz frequency. The rest of the post is devoted to the analysis of these measurements.

In-orbit testing of Es’hail 2 Amateur transponders

Yesterday, December 23, MELCO carried out some in-orbit tests of the Es’hail 2 Amateur radio transponders. Since Es’hail 2 is currently under commissioning, it was expected that at some point the Amateur transponders would be activated for testing, but no announcement of the tests was done in advance. At around 11:00 UTC, Rob Janssen PE1CHL, noticed that the narrowband transponder was active and a carrier signal was being transmitted through it.

Since then, I monitored most of the tests and sent updates on Twitter, together with other people (see also the posts in the AMSAT-DL forum). Without knowing the details of the test plans, we limited ourselves to watching and following the tests that were being made. If some schedule of the tests had been published in advanced, we could have thought, prepared and performed some interesting measurements on the downlink signals.

I understand that since these tests are carried out by MELCO, AMSAT-DL might not have the specific details, but still I think that AMSAT-DL is publishing very little information about Es’hail 2 events. It was only at 22:35 UTC that AMSAT-DL published a small note on Twitter about the tests. I think the greatest concern is that people start transmitting through the transponder, interfering with the tests. However, since news spread very fast these days through social media, I think that publishing more information rather than keeping things discreetly serves better to prevent people from using the transponder during the commissioning. In any case, I’ll repeat it here:

Es’hail 2 is currently under commissioning. The 2.4GHz uplink of the Amateur transponders should never be used until authorized by AMSAT-DL. The Amateur transponders will sometimes be enabled for in-orbit testing by the MELCO/Es’hailSat/AMSAT-DL engineers. Relax, sit back, and watch the tests on the 10GHz downlink.

I also think that publishing more information would be beneficial to educate the community of radio Amateurs. Some people have asked me about the concept of in-orbit tests. After a satellite is launched into orbit, the performance of all its systems is tested to ensure that it matches design specifications, simulations, and pre-launch tests done on ground. This is important to guarantee that any problems, malfunction or damage that occurred during the launch can be diagnosed and hopefully mitigated by activating backup systems or other reliability measures. In-orbit testing of large satellites can take several months, since there are many complex systems that need to be tested remotely.

In the case of the Amateur radio payload of Es’hail 2, MELCO is carrying out the tests, since the payload was built by MELCO according to the design specifications by AMSAT-DL. The kind of tests they are performing are related to the performance of the bent-pipe transponders. They sweep in frequency the transponders to make sure that the passband shape is as expected. They transmit carriers of different power levels to check for linearity of the transponder and AGC performance, and they try different gain/power level settings of the transponder power amplifier to make sure it performs correctly over all its working range.

This is a rough account of the tests that were made yesterday, using my tweets as a sort of activity log.

Recommendations for receiving Es’hail 2

A couple days ago, Janos Tolgyesi HG5APZ asked me by email about different hardware setups to receive the Amateur radio transponders on Es’hail 2, with an interest on inexpensive but effective solutions. He was quite happy with my detailed reply and convinced me to turn it into a blog post, so that other people can learn from it.

This post is intended for people that do not know much about Es’hail 2 but are interested in receiving it. If you’ve been investigating about the different setups that people are doing to receive it, then probably you’ll not learn anything new here. The post addresses questions such as “do I need a modified LNB” and similar.

Studying Es’hail 2 Doppler

Es’hail 2, the first geostationary satellite carrying an Amateur radio payload, was launched on November 15. I wrote a post studying the launch and geostationary transfer orbit, and I expected to track Es’hail 2’s manoeuvres by following the NORAD TLEs. However, for reasons not completely known, no NORAD TLEs were published during the first two weeks after launch.

On November 23, people found Es’hail 2 around the 24ºE geostationary orbital slot by receiving its Ku-band beacons at 10706MHz and 11205MHz. On November 27, NORAD TLEs started being published, confirming the position of Es’hail 2 around 24ºE. Since then, it has remained in this slot. Apparently, this is the slot that will be used for in-orbit test before moving the satellite to its operational slot on 25.5ºE or 26ºE.

Since November 27, I have been monitoring the frequency of the 10706MHz beacon to measure the Doppler. A geostationary satellite is never in a fixed location as seen from the Earth. It moves slightly due to imperfections in its orbit and orbital perturbations. This movement is detectable as a small amount of Doppler. Here I study the measurements I’ve been doing.

Es’hail 2 launch in GMAT

After a long wait by many Amateur radio operators, Es’hail 2, the first geostationary satellite carrying an Amateur radio transponder launched yesterday on a SpaceX Falcon 9 Full Thrust from the historical LC-39A pad in Kennedy Space Centre, which was used by many Apollo and Space Shuttle launches in the past.

Es’hail 2 is the second communications satellite operated by the Qatari company Es’hailSat. It was built by Mitsubishi Electric Corporation (MELCO). It carries several Ku and Ka band transponders intended for digital television, Internet access and other data services. It also carries an Amateur radio payload designed by AMSAT-DL, in collaboration with the Qatar Amateur Radio Society. The payload has two transponders, with S-band uplink and X-band downlink. One of the transponders is 250kHz wide and intended for narrowband modes, and the other one is 8MHz wide and intended for DVB-S and other wideband data modes.

SpaceX live-streamed the launch, and the recording can be seen in YouTube. Today, Space-Track has published the first TLEs for Es’hail 2 and the second stage of the Falcon 9 rocket. Here I look at these TLEs using GMAT.

Scanning Ku band satellites with the FUNCube Dongle

I’ve recently installed my satellite dish and modified LNBF in my garden. This equipment will be used to receive Es’hail 2, the first geostationary satellite carrying an amateur radio transponder. Here I’ll look at the hardware I’m using, how I did the alignment to the 25.5ºE geostationary orbital position where Es’hail 2 will be located, and how to have some fun scanning the direct broadcast satellites in the Ku band with a FUNCube Dongle Pro+.