Delfi-n3Xt Satellite

Delfi Nanosatellite Program Manager, Jasper Bouwmeester PC4JB, provides this update on the Delfi-n3Xt satellite which was launched November 21 and carries a 435/145 MHz linear transponder.

Dear Radio Amateurs,

Here is a status update about Delfi-n3Xt operations.

New DUDe telemetry client

Attached is an improved DUDe client. The phase locked loop is a bit more improved and the signal indicator is adjusted. The previous version indicated a center frequency of 1600 Hz, which was some heritage from Delfi-C3. The transmitted bandwidth of Delfi-n3Xt is about 4500 Hz, so with a center frequency of 1600 Hz the lower part of the band which would ‘virtually’ be below 0 Hz is actually reflected back inverted in the low audio frequencies causing more perceived noise. The best tuning center frequency is about 2200 Hz.

I have received many questions in the past weeks, so here are some hints to increase successful packet demodulation.

– The carrier frequency of the ITRX, which is currently the transmitter being on, is really close to 145.870 MHz. Please note however that the carrier is suppressed and we are actually transmitting in upper side band (USB). The receiver should thus be in upper side band and tuned to 145.870 MHz plus/minus Doppler. The center tuning frequency is the center of the USB signal, not the carrier. If your equipment allows this you can automate Doppler correction with e.g. WXTrack.

– The most optimal input level is when the signal strength indicator reaches about 25% of the slider. If the slider hits the red, distortion of the signal is already present. But even just below the red, we have discovered that packet loss is significant. In a next DUDe version we will adjust this slider such that it becomes intuitive again. If signal level is too high, adjust the gain of your receiver audio output first as if you are just adjusting the line-in or mic input of your sound card in the record volume control you may still overdrive your signal. This hint of course only applies to people which are not successful in receiving any other satellite (like Delfi-C3 ) yet with the same setup.

– The standard filter in the ICOM 910 receiver is about 2.5 kHz. This is too narrow for Delfi-n3Xt and demodulation becomes difficult. You will not reach a continuous packet demodulation if you do not have a bandwidth of at least 3.5 Khz. Most optimal is about 4.5 kHz.

– In case you use a software defined radio (e.g. the FunCube dongle) you can best record about 25 kHz and put a digital  4.5 kHz bandwidth filter around the signal. HDSDR software can support automated Doppler correction in combination with WXtrack.

– The TLEs have now named correctly “Delfi-n3Xt” in the TLE-new list.

– You may replay and SDR recording with DUDe open if during the pass you were not able to demodulate many packets. However, for our server it would be better to do this only once as otherwise the database will be flooded by duplicates. You can off course practice a bit first with an offline DUDe client. You can simply do this by extracting the attached zip file to a different folder an not using your log in details. In principle, an automated Doppler correction with the latest TLEs will already yield a very good result which can hardly be beaten by manual tuning.

– We kindly ask you not to share audio or SDR recordings with other radio amateurs, or at least ask them not to log in to our server with DUDe as we really would like to correlate the data to geographical location as well as the origin (see also the contest below).

Radio Amateur Contest

We are very grateful to all radio amateurs who are collecting telemetry or are attempting to. So far, we have seen less data coming from around the world than with our previous satellite Delfi-C3. Probably one of the main reasons is buggy telemetry client we have released before and the difficulties of demodulation a 2400 bit/s with many equipment. I hope the new DUDe client and the hints above will help many of you to demodulate Delfi-n3Xt data. A possible second reason is that we are not unique anymore with the tens of CubeSats being launched in the past months. Therefore we would like to do something back to the radio amateurs taking the effort to receive our latest satellite. We will soon announce a contest where we will provide prizes to radio amateurs with high packet rates in our database. You can see the top 50 here:  http://delfi-n3xt.lr.tudelft.nl/statistics.php . Prizes and rules are still to be determined, but you can already start increasing your packet rates as we will start counting from the launch date. Our own ground station is of course excluded.

Satellite Status

In the past weeks we have seen that the batteries became more and more discharged. Also during passes we noticed that the incoming power was fluctuating more than expected, sometimes even causing the satellite going in to eclipse mode with the radio off in the Sun. We have discovered the cause of this. The maximum power point trackers go into an sleep mode if there is insufficient power to overcome their own consumption for 15 seconds. It is activated every 25 seconds to check the latest power status. If the satellite is tumbling more than 14 degrees/s, this is not a problem as we reach sufficient power within 15 seconds (hence no sleep mode). If the satellite is however tumbling between 1 deg/s and 14 deg/s, the power tracker is many times in sleep mode and misses part of the incoming energy because of the 25 seconds wait time. Below 1 deg/s the problem becomes less again. As we are successfully detumbling to about 2-4 deg/s, but have not yet been able to tweak attitude parameters such that we go below 1 deg/s we have this issue. We have decided to turn of the power hungry subsystems, including attitude control and S-band transmitter to recharge the batteries and think of a more sustainable solution. Don’t be shocked if you see a lot of odd parameters, like undeployed solar panels, as these are just zeroes in the data.  Please note that the S-band transmitter is currently off, so there is no signal at 2405 MHz.

73,

Jasper Bouwmeester PC4JB
Delfi Nanosatellite Program Manager &
Researcher Small Satellite Technology
Chair of Space Systems Engineering
Delft University of Technology

Telemetry reception http://www.delfispace.nl/operations/delfi-n3xt-telemetry-reception

Delfi-n3Xt http://www.delfispace.nl/operations/radio-amateurs

Dnepr Yasny launch https://amsat-uk.org/satellites/dnepr-november-2013/