Testing Opera sensitivity with GNU Radio

Some fellow Spanish Amateur Operators were talking about the use of the Opera mode as a weak signal mode for the VHF and higher bands. I have little experience with this mode, but I asked them what is the advantage of this mode and how it compares in sensitivity with the JT modes available in WSJT-X. I haven't found many serious tests of what is the sensitivity of Opera over AWGN, so I've done some tests using GNU Radio to generate signals with a known SNR. Here I'll talk about how to use GNU Radio for this purpose and the results I've obtained with Opera. Probably the most interesting part of the post is how to use GNU Radio, because it turns out that Opera is much less sensitive than comparable JT modes.

Continue reading "Testing Opera sensitivity with GNU Radio"

Some measurements of CAS-2T on orbit 25

Last Thursday, a CZ-11 Chinese rocket launched from Jiuquan. Alan Kung BA1DU posted in amsat-bb some minutes after launch saying that this launch contains an Amateur payload: CAS-2T. As it is usual with Chinese Amateur satellites, little information is available publicly and we hadn't heard about CAS-2T before.

According to BA1DU, CAS-2T is a 2U Cubesat with a CW beacon on 70cm and a V/U FM transponder. The satellite will not separate from the upper stage of the rocket, so it will decay between 10 and 30 days before launch. However, this is not correct. After launch, CAS-2T was identified as object 2016-066E by Mike Rupprecht DK3WN using Doppler measurements. This object is on a 1030km x 500km elliptical orbit, so it will not decay soon. Apparently, due to a problem in the launch, the upper stage of the rocket has being put in this 10 year+ orbit. Indeed, there are radar TLEs for 6 objects from this launch. Four of them are on circular orbits of roughly 500km height, while the other two are on elliptical orbits of 1030km x 500km radius. All of these orbits will last for many years.

Reports of CAS-2T from Amateurs worldwide agree that the CW signal has good strength, but it suffers much fading. Unfortunately, the FM transponder does not function properly. It seems to respond well to an uplink signal, but it doesn't modulate properly, as if it lacked power or suffered some other problem. On Friday afternoon, I took an SDR recording of the CW and FM signals of CAS-2T during its orbit 25. Here I show some measurements of these signals. The recording was done with a 7 element yagi and a FUNcube Dongle Pro+, and it has been Doppler corrected using the TLE for object 2016-066E, which gives a very good match.

Continue reading "Some measurements of CAS-2T on orbit 25"

Concurso QSL V-UHF

Today I've hiked to Cerro de San Pedro, SOTA summit EA4/MD-020 (1425m), to work in the last national V-UHF contest of the year: concurso QSL. This contest is a bit particular, because it coincides with the IARU-R1 UHF & up contest, so the contacts in the UHF & up bands count for both contests. As always, I'm participating in the 6 hours category with my QRP station: a FT-817ND with 5W and a 3 element yagi on 144MHz and 7 element yagi on 432MHz (the Arrow satellite yagi).

I arrived at the summit at 8:00UTC and worked until the end of the contest, at 14:00UTC, so I could enjoy almost 6 full hours of operation. As expected, after 12:00UTC there where few people left in the contest, as almost everybody had gone for lunch. The map of stations worked is below. Stations in green where worked both on 144MHz and 432, stations in blue where worked only on 144MHz and my operating position is marked in red.

Participation has been perhaps a bit low and propagation was not so good at times, but overall I'm happy with my results, which compare well with other contests this year. I missed some usual stations from the zones EA3 and EA5. I think that propagation to these zones was only open briefly during the contest.

IARU R1 145MHz contest

Today I hiked with all the family to La Najarra, SOTA summit EA4/MD-013 (2122m), to participate in the IARU Region 1 145MHz contest. Unfortunately, for some weird reason very few stations in Spain participate in this contest. My plan was to make a combined contest activity and SOTA activation, making QSOs with whoever was working SSB in the contest, but spending most of the time calling in FM. This gives me the opportunity to contact many more stations, because not many hams have a VHF yagi and SSB radio, but many have a VHF vertical and FM radio. It also gives these local hams the possibility to work a SOTA summit (most SOTA activity is in HF here) and work some DX with a quite basic FM station (100km or more are easy to achieve).

I worked from around 9:30UTC to 11:30UTC. The station was, as usual, an FT-817ND with 5W and an Arrow satellite yagi (3 elements).

I've put in the contest log all stations that were able to give me their locator (many hams that work only FM have no clue about what locators are). This is OK with the contest rules. The other stations went only to the SOTA log. Below, you can find the map of contest contacts. I made a total of 17 contacts, but, of course, I can't put on the map the stations that didn't know their locator.

How hard is it to decode 3CAT-2?

In a previous post, I looked at the telemetry packets transmitted by the satellite 3CAT-2. This satellite transmits 9600bps AX.25 BPSK packets in the Amateur 2m band. As far as I know, it is the only satellite that transmits fast BPSK without any form of forward error correction. LilacSat-2 uses a concatenated code with a (7, 1/2) convolutional inner code and a (255, 223) Reed-Solomon outer code. The remaining BPSK satellites transmit at 1200bps, either using AX.25 without FEC (the QB50p satellites, for instance), or with strong FEC (Funcube, for example). Therefore, I remark that 3CAT-2's packets will be a bit difficult to decode without errors. But how difficult? Here I look at how to use the theory to calculate this, without resorting to simulations.

Continue reading "How hard is it to decode 3CAT-2?"

Decoding packets from 3CAT2

On 15th August, a Chinese CZ-2D rocket launched three satellites from Juiuquan (Mongolia). The main payload was the Chinese satellite QSS, designed to do some experiments in quantum communications and entanglement. As anything that has the word quantum on it, this satellite even made it to the mainstream news in Spain. The rocket also launched Lixing 1, another Chinese satellite which will research the upper atmosphere, and 3CAT2, from the Universidad Politècnica de Catalunya (Spain).

3CAT2's main payload is a GNSS reflectrometer designed to measure the altitude of the Earth and map the oceans. This means that it uses reflections of satellite navigation signals off the surface of the earth and sea to perform mapping. It will mainly use the L1 and L2 signals from GPS, but it can also work with Galileo, GLONASS and BeiDou signals. It also carries a prototype of a magnetometer designed for the eLISA project. This project consists in setting up a laser interferometer in space to observe gravity waves. It is roughly the same as the Earth-based LIGO, that recently confirmed the first detections of gravity waves. However, since eLISA will be in space, its laser arms will much longer than LIGO's. This permits to study much lower frequencies than it's possible Earth-based interferometers.

3CAT2 has a downlink in the Amateur 2m band, at 145.970MHz, and transmits 9600bps BPSK. It also has a faster BPSK downlink in the S-band, presumably at 2401MHz (inside the Amateur 13cm band). The days following 3CAT2's launch I tried to receive its VHF signal, without any luck. I have been in contact with other Amateurs who also listened and didn't hear anything.

This morning, I've received email from Scott K4KDR telling me that he has heard the satellite for the first time and he has managed to do a recording, but he is unable to decode the data.

We where unsure about which encoding that 3CAT2 is using. It could be AX.25, or some custom protocol using FEC. As far as I know, the only other satellite that transmits 9k6 BPSK in the Amateur bands is LilacSat-2, which uses strong FEC. Nevertheless, I've taken a good look at Scott's recording and I've been able to decode one packet. This is, as far as I'm aware, the first decoding of 3CAT2 by an Amateur operator.

Continue reading "Decoding packets from 3CAT2"

Recovering an RS92-SGP radiosonde

A few days ago, I talked about the radiosondes that are launched every 12 hours from Madrid-Barajas Airport. Yesterday, I went with my mother on a trip to try to recover the radiosonde that was launched at 11:00UTC. This radiosonde managed to ascend to 31000m before bursting. This is quite high for a radiosonde of this kind, as they usually burst between 24000 and 28000m.

We left home at 13:00UTC, so the radiosonde was quite far from us by that time. The last telemetry we managed to decode was when the radiosonde was 3800m high and on its way down. It was flying over Sacedón, in Guadalajara, and slowly drifting eastwards along the road. We were still on our way to Guadalajara, more than 40km away.

Continue reading "Recovering an RS92-SGP radiosonde"

Receiving the Vaisala RS92-SGP radiosonde launched from Madrid-Barajas

Each day, at 01:00UTC and 11:00UTC a Vaisala RS92-SGP radiosonde is launched from Madrid-Barajas airport. This is a small electronics package tied to a helium balloon that ascends up to between 24 and 28km high before bursting and descending on parachute. It is designed to measure atmospheric parameters on its way up. It includes temperature, pressure and humidity sensors, as well as a GPS receiver. The launch on Wednesdays at 11:00UTC also includes a plug-in ozone sensor (which is a much larger and more expensive package). The data is transmitted at 403MHz using Manchester-encoded 4800bps GMSK and protected using Reed-Solomon. You can find more information about the RS92-SGP model in its technical datasheet and about the launches at Madrid-Barajas and other launches in Spain in the Spanish AIP Section 5.3 (other activities of a dangerous nature). Also, there is somebody who feeds the radiosonde data into the APRS network using SM2APRS, so you can track the launches by following OKER-11 on aprs.fi.

Usually, the Sondemonitor software is used to receive and plot the parameters measured by the radiosonde and track the GPS data. Of course, this program is very nice and complete, but it is shareware, costs 25€ and runs only in Windows. I wanted to try if it is possible to track the GPS data in Linux using free software.

Continue reading "Receiving the Vaisala RS92-SGP radiosonde launched from Madrid-Barajas"

Concurso Nacional V-UHF

Today I've hiked up with my father to Siete Picos, SOTA summit EA1/SG-005 (2138m), to participate in this month's national V-UHF contest. We arrived and set up around 07:30UTC and worked until 11:30UTC, where activity became low, as most possible contacts were already done and people started to leave in order to prepare lunch. The equipment was a Yaesu FT-817ND and an Arrow yagi antenna (3 elements in 144MHz and 7 elements in 432MHz).

Below is the map of stations worked. My position is in red, stations worked both in 144MHz and 432MHz are in green and stations worked only in 144MHz are in blue. The black station is the odd one that I could only work in 432MHz. This can happen if you catch them first in 432MHz, then a big mess with several stations arises and you're unable to tell them to change to 144MHz to make the contact and decide that you'll catch them in 144MHz later, but you don't manage to find them later.

Continue reading "Concurso Nacional V-UHF"

Concurso Atlántico V-UHF

Today, I've participated in this month's national V-UHF from Cerro de San Pedro, SOTA summit EA4/MD-020 (1425m). I arrived the summit a bit before 10:00UTC and worked until the end of the contest (14:00UTC). The equipment was the usual: a Yaesu FT-817ND and an Arrow satellite yagi antenna (3 elements in 144MHz and 7 elements in 432MHz).

Find below the map of stations worked. My location is in red, stations worked both in 144MHz and 432MHz are in green and stations worked only in 144MHz are in blue.

Continue reading "Concurso Atlántico V-UHF"