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IK0WRB

Using Qatar Oscar 100

Qatar Oscar 100 is a radio amateur satellite, or actually radio amateur equipment put aboard the TV satellite Es'Hailsat 2, in geostationary orbit at around 25.5 degrees east. This is the first geostationary radio amateur satellite ever.
It has two transponders, one for narrow band transmissions and the other dedicated to wide band, useful for DATV (Digital Amateur TV).
The following pictures, got from some web sites, show the satellite coverage and the allocation of frequencies. As you can see, the input is 2400-2400.5 and 2401.5-2409.5 MHz, while the output is 10489.5-10490 and 10491-10499 MHz.


  

Receiving

Starting February 5, 2021, I can receive the narrow band QSOs from QO-100, because I installed a few devices on the dish I have been using for TV for several decades. The dish was aiming at 13 East, with a second LNB at 19.2 East and in order to aim also at 25.5 East, I moved it to point the central LNB at 19.2 East and the right one at 13 East. This way the third feed to the left can easily reach the 25.5 East of QO-100. In the following picture you see the method I used.
 

The following video shows the first signals received while working at the dish on the roof.


When switching on, the converter is not stable at all. This picture shows the lower CW beacon on the WSJT-X waterfall. The interval among horizontal lines is 15 seconds.
 

However, after about 8 minutes, it becomes quite stable.


I find this is almost perfect, but there is a product missing on the market today, which would enable to receive both DATV and narrow band signals with ease.
I am thinking about a modified tv sat LNB, with the following features:
  • Lower LO at 9491 MHz (it could be in the range 9000-9500)
  • Higher LO at 10056 MHz
  • Possibly OCXO controlled

The cable from the LNB would go into a standard and cheap sat/earth demux. The sat part would go into a standard DVB-S2 receiver/decoder and the terrestrial part into a 70 cm band receiver. At this point using the sat decoder we could:
  • Set the lower LO and H pol., to receive DATV on the tv at 1000-1008 MHz
  • Set the higher LO and V pol., to receive SSB/CW signals on 430.5-431 MHz
If we can afford to receive on the 23 cm band, there could be a single LO at 9193, to receive narrow band at 1296.5-1297 MHz and the DATV at 1298-1306 MHz. However in this case the sat/earth demux would not work, so we would have to phisically attach the cable to one equipment at a time and when on the 23 cm rx we ought to provide 13 V with a DC bias. For these reasons I think that the solution with a double LO is perhaps better.
By the way if you are interested only to the narrow band signals, you can use the most popular method:
a standard tv LNB set in V pol. with a 13 V DC bias and a receiver at 739.5-740 MHz (SDR, SSB scanner, etc.).

Transmitting

Starting February 22, 2021 I can also transmit to the satellite. The following picture shows the transmitting schema.
 

At the moment I am using an Icom IC-706MkIIg as transmitting rig, which cannot transmit at the low levels required by the transverter input. So I did set the transverter gain to the minimum and I used RG58 cable, quite lossy at 144 MHz (on purpose!).
This way my descent has about 6 dB of loss and I can transmit up to about 20 W at 144 MHz, which will translate to about 5 W at the transverter input.
This would give me 1 W at 2.4 GHz, but wait! There is the cheap WiFi amplifier after, and it accepts only up to about 100 mW! So actually I drive the transverter at 2 W (0.5 W on the roof) and the RG58 attenuation is really part of the game.
Why I did not use simply an attenuator? Well, I had to lay out a new cable in a busy Rome building, so a cable which is thin, light, cheap and had the right attenuation was just perfect!
To regulate the power levels, lacking wattmeters for the 13 cm band, I looked at the specs, then I measured the current at tx with no signal and with signal.
I already made several contacts, in SSB, CW and FT8.
I also listened to transmissions in RTTY and SSTV. Really beautiful!
During the first days, I opened sometimes the web sdr site at websdr.is0grb.it:8901, to see the whole band at a glance and quickly tune my receiver to the signals. However, now I am not using it anymore, relying only on the manual sweep of the band.
 

Since this web sdr is GPS controlled, it is useful to check the drift of your transmitter. It turned out that the DB6NT transverter is very stable indeed!
 
This is my transmitting dish. I used RG-213 from the amplifier to the helix, because I had it available and here RG-58 is too lossy, 1 meter would lose about 1 dB!
For now it is ok this way, but perhaps I will replace the RG-213 with a shorter cable with RF-240.
 

Digital modes on the satellite

Besides SSB and CW, I tried using also several digital modes on this satellite. There is some activity in FT8 on 10489.540, in RTTY a bit higher and in SSTV, both analog and digital, around 10489.580 - 10489.620. I made some QSOs in FT8 and RTTY and even one in Feld-Hell!
Perhaps we could also try FT4, because there is almost no low signal issue, although it is more time critical. We should experiment.
I think a good digital mode could be THOR, because this MFSK mode encodes data using the difference in frequencies, not the absolute frequencies. So, I suppose, it should be more forgiving of the frequency drifts that many experience, due to unstable LNBs or upconverters. I tried moving the receiving frequency up to 150 hz while transmitting and no characters were lost! The CQ mode is THOR11 and if you want to try with a sked, please contact me at mycallsign@tiscali.it
To use digital modes under Linux, I launch two copies of Flgidi. The first copy of the program starts receiving. When I launch the second copy of Fldigi, it cannot use the audio card for receiving, because it is in use by the first copy, but I can use it very well for transmitting, also due to the fact that the audio card for tx is a different one (USB cable audio for rx and internal audio for tx).
This way I can monitor my own digital transmissions as they come back from the satellite. Thus, I can tune everything to go in an almost perfect iso frequency.
 
When I work in FT8 of FT4, however, I use a single copy of the program, so I don't monitor my transmissions. Yet to try, if it's possible...

September 2022

I did not use QO-100 for many months, then, when I came back from the 2022 summer holidays, I wanted to try it again, but I found that the DG0VE downlink converter was broken. I don't know why this happened, perhaps it was due to a lightning or something similar.
So I had to change my setup and, since DG0VE is sk, I bought a TCXO controlled LNB. This simplified the setup on the roof, but now the signal I have to receive is in the 739.5 - 740 MHz range. Happily enough, I had an SDR receiver in my drawer, so I connected it to my PC.
Using the GQRX program under Linux, I tried receiving all SSB transmissions from the satellite and make QSO in this mode.
I could also use CW, even if the tuning on GQRX is not that easy. For digital modes I was planning to install a 739 MHz to 50 MHz converter, so to use my HF radio as a receiver again, for all modes.
Unfortunately on October 11 I received a phone call from Germany, telling me that the downconverter, by the Italian firm Elad, is temporarily out of production, for the lack of electronic components.
Thus I switched my mind from hardware to software. On the same day I installed on Linux the Jack package and after some try I succeded in routing the output of the program I am using now, CubicSDR, to the input of WSJT-X. At the same time the output of WSJT-X goes to the sound card, where it goes to the mic input of my IC-706MkIIg. So now I am back to FT8 on QO-100! (and without spending a cent).
The only problem is the lack of stability, so QSOs are possible only at times. The LNB is TCXO controlled, so the source of thermal instabilities can only be the HackRF One receiver and/or the PC itself. I am planning now to add a TCXO external oscillator to the receiver, which can be only beneficial to the overall stability of the receiving chain.
Here it is my lastest setup.

November 2022

I added a 10 MHz external OCXO to the HackRF SDR receiver, but this did not change things too much. Apparently it is the LNB that it not as stable as announced, although it contains a TXCO. QSOs are possible in all analog and digital modes, with the notable exception of FT8, workable only at times.
For now, I will stick to this configuration. Meanwhile I am studying possible cheap GPS modules able to produce a rock stable 10 MHz signal, transforming it to 25 MHz (it exists a chip for this!) and feeding it to a modified LNB. It is a pity no one sells a GPS-driven LNB!

December 2022

The cheap 10 MHz OCXO broke, but this was not a big problem, since the SDR stability was almost the same. I worked many stations in SSB and FT4 and even in FT8, when the external temperature was not moving fast.
I noticed that some stations updload their satellite QSOs to Lotw the wrong way. They do not specifiy that it is a sat QSO in the adif file!
As an example, I show here the row of a satellite QSO, that way it should be (data is not real):
<QSO_DATE:8>20221228 <TIME_ON:6>093600 <BAND:4>13cm <MODE:3>SSB <CALL:5>TF1ZX <PROP_MODE:3>SAT <SAT_NAME:6>QO-100 <BAND_RX:3>3cm <EOR>
It is important that at least the "<PROP_MODE:3>SAT" is present, otherwise Lotw will think this is a tropo 13cm QSO and it will never match the corresponding QSO.
See you on the satellite!
Vinicio, IK0WRB