Difference between revisions of "Receiving Oscar 100 DATV signals"
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Revision as of 18:56, 21 September 2021
Oscar 100 has an 9 MHz wide band transponder dedicated to Digital Amateur Television.
The transponder spectrum can be monitored using the online spectrum monitor: https://eshail.batc.org.uk/wb/ However, to receive and decode the signals you will need to set up your own receiving station
- 1 Setting up the receive station
- 2 What receiver to use
- 3 Setting up your receiver
- 4 QO100 Live Tune
- 5 Further information
- 6 Typical receive results
Setting up the receive station
A typical DATV receive system will consist of the following:
To receive the DATV signals you will need at least a 90cms dish and preferably 1m or larger - see this guide as to how to align your dish on the Es'hail-2 satellite: https://wiki.batc.org.uk/Es%27hail-2_Basic_Information#Aligning_your_dish
Just like any consumer satellite system, you will need an LNB at the dish to convert the 10GHz Ku band signals down to L Band which can then be decoded by the satellite receiver.
Whilst any modern Ku band satellite LNB will receive the Oscar 100 signals, particularly the 2Ms beacon, it is recommended that you use a Phase Lock Loop LNB. This is because the frequency stability of a standard DRO unit will make it difficult to receive the Narrow Band transponder SSB signals and Reduced Bandwidth DATV (RB-TV) signals on the wide band transponder.
The most common unit is the Octagon Optima PLL OTLSO LNB (Beware there are a number of other Octagon units available which are standard DRO LNBs – ensure you buy the OTLSO PLL unit).
See this page for more details: https://wiki.batc.org.uk/Es%27hail-2_LNBs_and_Antennaes
Note - it is recommended that you do not do any modifications to lock your LNB to an external source for DATV reception as it is beleived that these modifications can make DATV reception worse as they increase the phase noise of the LNB.
The DATV transponder is horizontally polarised - this means the DATV receiver will need to be capable of providing 18v DC to the LNB to select horizontal polarisation required for the wide band transponder.
All satellite receivers can do this - select LNB voltage in set up - and when using MiniTiouner this can be done by using a step up regulator from 12v (plenty on ebay) and feeding 18v in to F2 and put J3 and J4 links in to fed the selected LNB. https://wiki.batc.org.uk/images/6/6d/SERIF.pdf
Alternatively you can physically rotate the LNB through 90 degrees offset so the cables are coming out of the side and then just fed it with 12v.
What receiver to use
The frequencies in use are not standard satellite frequencies and the bit rates we use for ATV are lower than commercial satellites, the choice is limited.
To receive the wide band horizontally polarised DATV transponder you will need a DATV receiver capable of receiving 741 MHz to 749MHz.
Unfortunately this is outside the normal fequency tuning range of a standard consumer digital TV Set Top Box (STB). Therefore you will either need an additional up converter to shift the IF frequency up to be in the tuning range of the STB at L-band between 950 – 2150MHz. A Global ADX-Plus, an original Astra frequency extender or an SUP2400 converter previously sold by BATC will work.
Alternatively you can modify your PLL LNB by changing the 25MHz reference crystal to 26MHz to produce an IF output above 950MHz.
Standard satellite receivers
Once you have an upconverter or modified LNB you will be able to use a Free to Air DVBS2 (HD) receiver to receive the DATV beacon signal on 10,491.5 MHz which is transmitted using DVB-S2 1500 kS. Note, it must be a satellite receiver, not a terrestrial Freeview box, and a Sky box or similar service branded satellite box will not work - it must be a Free to Air (FTA) satellite box.
However, you will NOT be able to use most (95%) of consumer STB's to receive the Reduced bandwidth (RB-TV) signals which are typically 333Ks on Oscar 100.
However, there is a USB tuner designed specifically for Amateur TV use which natively covers 143MHz to 2450Mhz and is suitable to receive Es’hail-2 and a number of amateur bands with no modifications or additional up-converter.
The other reason why MiniTioune is the preferred solution to receive the DATV transponder is that most amateur TV transmissions are using Reduced Bandwidth DATV (RB-TV) with a bandwidth below 1 MHz - to date 90% of the DATV transmissions on Oscar 100 have used RB-TV. A standard consumer STB will not receive these RB-TV signals but MiniTiouner has been designed to receive RB-TV signals with bandwidths down to less than 100 KHz bandwidth.
MiniTiouner hardware is available from the BATC and other sources and are used with the MiniTioune software developed by F6DZP to receive and decode the signals. See https://wiki.batc.org.uk/MiniTioune for more details.
Standard SDR software and hardware do not as standard receive DATV signals however, there are 2 programs for the advanced user which may work at some symbol rates:
Setting up your receiver
You will find it a lot easier to tune to the DATV signals on Oscar-100 if you put your LNB offset in to your receiver rather than try to enter the IF frequency such as 741.5MHz directly.
Most LNBs have a 9750 MHz local oscillator - when 9750000 is put in to your receiver offset (on MiniTiouner it is the white box directly below the frequency box) you can then just enter the 10 GHz freq shown on the spectrum display directly into your receiver.
Tuning to the signals
Once you have the system set up and you have successfully received the DATV beacon on 10491.5 MHz 1500 kSS DVB-S2 you will be ready to receive DATV signals.
All signals should appear on the channels listed in the bandplan: https://wiki.batc.org.uk/Es%27hail-2_DATV_Bandplan
Because you need to know a number of parameters before you can start to receive a signal, BATC has set up a dedicated chat line beside the spectrum monitor https://eshail.batc.org.uk/wb/
When you see a signal appear on the spectrum monitor, check the chat and enter the frequency, symbol rate (SR) and DVB-S or DVB-S2 mode in to your receiver. Once you have received the signal make sure you let the station know you have received them!
If you have the correct symbol rate set for a signal, you may find the receiver AFC may pull your receiver on to the frequency. Therefore you may find you receive the beacon on 10491.5 MHz when your receiver is tuned to 10493MHz.
For more details on how to use MiniTioune see this page https://wiki.batc.org.uk/MiniTioune_software
QO100 Live Tune
Rob M0DTS has developed a small application designed to run on a PC that grabs the fft data from the BATC Wideband Spectrum monitor page and allows the user to click on signals which automatically configures Minitioune to the required settings to receive the signal via udp control. See QO100 Live Tune for more details and download instructions.
There is a lot of information published on this wiki and also more discussion on the BATC forum here: https://forum.batc.org.uk/viewforum.php?f=101
Typical receive results
QO-100 DATV beacon - 10491.5 MHz, DVB-S2 1.5 MS FEC 4/5
Since the beacon was reduced in bandwidth to 1.5 MS, the following results are typical:
|Dish size||Received MER|
When the beacon was 2 MS, the maximum MER possible was is 11.7 dB, limited by uplink C/N.
Readings from the old beacon: measured using MiniTioune V0.8s and with DVB-S2 (not auto) selected.
|Dish size||Received MER|