Making life hard for DXers – or: tV stations’ little ...tele-audiovision.com/TELE-satellite-1209/eng/feature-transmission.pdfMPeG 4:2:2 feed from the German parliament. a standard

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156 TELE-satellite International — The World‘s Largest Digital TV Trade Magazine — 09-10/2012 — www.TELE-satellite.com

Special transmission Modes

Making life hard for DXers – or: tV stations’ little tricks to avoid viewersthomas Haring

Transmissions that are broadcast via satellite usually can be received by anyone within a particular satellite’s footprint. In the case of DTH (direct to home) TV and radio reception this is a welcome scenario, because providers are trying to max out on potential audiences. On the other hand, programs also need to be distributed within and between different providers without any viewers being able to receive them. In satellite speak these transmissions are called feeds. Feeds can be used to transmit a baseball game from the US, for example, or a live report from a news event.

a motorised antenna is required for feed reception

In europe the most popular multi-feed reception system is aligned towards aStra 19.2° east and HOtBIrD 13° east. Feeds cannot be received with such a set-up.

SCPC reception with only 1.6 Ms/s

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In both cases, TV stations do not want any unwelcome viewers for their feeds, because they only want the final product to reach households, including commercial breaks. This is why trans-missions between studios or TV sta-tions frequently use fibre optic cables to make sure only the two transmission partners can access material.

Luckily for satellite DXers, in today’s world a cable cannot always be used, for example if the distance is too large or if no cable is available on site to send a live report to station headquarters. In these cases, satellites have to be used for feeds.

Of course all sorts of technical tricks are used to limit the number of onlook-ers and the following account lists major strategies TV stations rely on:

encryptionThis is the most effective protec-

tion against unwanted viewers and for studio-to-studio transmissions this in most cases does not pose a challenge from a technical point of view. With out-side broadcast (OB) vans it’s a different story altogether.

While most OB vans are equipped with encryption hardware, time is of the essence in live reports so that setting up the required encryption is frequently not possible as it takes some time until all parameters are set and checked. Generally, feed transmissions fall back on directly addressable encryption sys-tems such as PowerVu or BISS. The latter, in particular, is protected by a password that is defined by the TV sta-tion.

Even if you try as hard as you can with the help of BruteForce luck will probably not be on your side in finding the correct password during the short time most feeds last. After all, the BISS password consists of 16 hexadecimal digits.

Counting down to the beginning of a feed transmission

MPeG 4:2:2 feed from the German parliament. a standard receiver would not be able to process this signal. With a PC and appropriate software the signal turns into nice video on the PC monitor.

Fashion tV on aBS1 75° east with an FeC of 7/8.

List of today’s feed transmissions

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If a feed is used to transmit content that is protected by copyright laws (for example a rock concert with clearly specified exploitation rights) TV stations will go out of their way to make sure the feed is fully encrypted. If the content is in the public domain anyway the meas-ures used by TV stations generally are less stringent but at the same time lock out as many potential viewers as pos-sible.

Selection of satelliteUsing a popular DTH satellite for feeds

always results in a comparably high number of unintended viewers. In addi-tion, the cost for using hugely popular positions such as ASTRA 19.2° East or HOTBIRD 13° East is enormous, so why would a provider select these birds for feeds in the first place? Dozens of less known satellites are available for that very same purpose and apart from being considerably less expensive they cannot be received by 99% of satellite antenna owners.

In Europe, the most frequently used satellites for feeds are EUTELSAT W2 at 16° East, EUTELSAT W3A at 7° East, EUTELSAT W1 at 10° East or TELSTAR 12 at 15° West for feeds to and from North America, ATLANTIC BIRD 1 at 12.5° West and PAS3R auf 43° West as the westernmost option. Unless you own a motorised dish or top-notch multi-feed antenna you’ll be left without a chance to receive signals from these positions.

MPeG 4:2:2For many years, TV stations have tried

to lock out viewers from feeds using modified colour sub-sampling. Digital TV reception via satellite generally uses the 4:2:0 standard which is characterised by identical colour sampling in both spatial directions, similar to the system used for compressed JPEG images.

MPEG 4:2:2, on the other hand, fea-tures a slightly different colour sampling process which distinguishes between horizontal and vertical colour sampling. Colour sub-sampling has its origin in the analog NTSC colour system and is used for digital video signals based on the ITU-R BT 601 norm.

With MPEG 4:2:2 horizontal colour sampling has only half the size of ver-tical colour sampling, yet this differ-

ence does not result in different colour resolutions for the two spatial directions because of interlacing that is inherent in the analog PAL and NTSC standards. Special receivers are required to cor-rectly process and display such sig-nals and because these receivers are designed for professionals only they carry a rather hefty price tag and thus are unaffordable for most amateurs.

However, most new Linux-based receivers allow real-time streaming of satellite signals to the PC using the built-in network interface. On the PC software decoders (which are available from the Internet at little or no cost) can take over decoding MPEG 4:2:2 sig-nals and display feeds for DX enthusi-asts.

Low symbol rateThis is a clever trick used to make

sure transmissions cannot be received by just about anyone. Almost all DVB-S receivers available today are able to process symbol rates between 2 and 45 Ms/s, with the symbol rate denot-ing the number of changes of state per second of the carrier signal. This is not to be confused with the bit rate which specifies the number of bits transmit-ted per second and thus is an indication of the video quality of a specific chan-nel. However, the two values are in fact interdependent as a low symbol rate automatically means that less informa-tion can be transmitted and as a conse-quence the bit rate used must also be lower.

This means that using a low symbol rate for feeds is a delicate balancing act for TV stations. On the one hand they want to lock out as many unwanted view-ers as possible by using a low symbol rate, but on the other hand too low a symbol rate automatically reduces video quality, which of course is an absolute no-go in the professional world.

In the end, mainly symbol rates between 5000 and 6000 Ks/s are used, which does in fact leave out a substan-tial proportion of DTH viewers, but still allows transmitting a high-quality signal.

Naturally, there are some examples for extremely low values, such as signal feeds of some Italian channels on NSS7 at 22° West which use symbol rates of way below 2000 KS/s and there-fore cannot be received on most digital boxes.

Well-known feed hunters from all over the world:

applesat from Beijing, China

Feed hunter rini from amsterdam, Netherlands

roy Carman from London, england

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Now you might wonder what it is that so many receivers encounter troubles with low symbol rates, while a few brave boxes seem to be unaffected at all. The root problem lies in the quality of the tuner as well as in software fine-tuning. If a transponder with extremely low symbol rates comes in, the bandwidth has to be reduced exactly in line with the symbol rate in order to arrive at a low noise level and achieve an optimum carrier-to-noise (C/N) ratio.

In turn, the frequency has to be main-tained even more precisely for a stable and reliable signal. Many manufactur-ers are trying to cut costs both in the hardware and the software fine-tun-ing fields, which consequently creates problems with ultra low symbol rates. Yet, manufacturers are hardly to blame as their specifications in most cases explicitly state that only symbol rates of 2 MS/s and above are supported.

Low FeCIf a high-capacity transponder is

required for a feed and the symbol rate cannot be reduced TV stations have the additional option of reducing the For-ward Error Correction (FEC). FEC is a mathematic correction process to set off signal errors that occur during satel-lite transmission. If it weren’t for this process, most of us would never be able to enjoy reliable satellite reception with reasonably small antennas.

The FEC N/M value specifies how many M (gross) bits need to be trans-mitted for each N (net) bit. An FEC of 1/2 therefore means that two gross bits are required for each net bit, with 3/4 it is four gross bits for 3 net bits and so on. The higher the FEC value, the lower the possibilities of mathematically cor-recting a faulty signal. If, for example, an FEC of 7/8 is in place you will need a very large antenna for reliable recep-tion.

So basically, the FEC defines the size of the required antenna and this way the FEC of a transponder can be modified to allow for either easy reception with an FEC of 1/2 or very difficult recep-tion with an FEC of 7/8. As a matter of fact, the new DVB-S2 standard brought about even more FEC modes such as 2/3, 3/5, 4/5, 8/9 or 9/10.

Juan Carlos Duarte from Santiago, Chile

Vincent Witjhun from Pontianak, Indonesia

Ingo Salomon from Johannesburg, South africa

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transponders lyingclose to each otherThe reception parameters required

by standard users for their satellite receivers are average values. In other words, a transponder with a specified frequency of 12,600 MHz in general is not received at precisely this frequency but rather at an optimum frequency of, say, 12,598 MHz.

This deviation between nominal and optimum frequency is caused by the LNB converter and cables, among others. Digital satellite receivers are designed to detect the optimum frequency and adjust their internal reception param-eters accordingly.

Strong transponders with sufficient spacing between each other therefore hardly cause any problems due to this impreciseness, but SCPC transponders with identical or similar symbol rates, which are close to each other and of which one transponder is significantly stronger than the other will cause receivers to lock the stronger tran-sponder and ignore the weaker tran-sponder.

The situation is aggravated by the fact that only very few receivers for pri-vate users still have the option of limit-ing the reception bandwidth, which can be used to force the receiver to select its frequency from a very limited range.

The result of all this is that TV stations can easily hide individual transponders behind others. If you’re eager to find out how your receiver at home copes with this, you can try to receive hori-zontal channels between 11,619 MHz and 11,645 MHz on NSS7 at 22° West. The same is true for channels between 12,507 MHz and 12,655 MHz on EUTEL-SAT SEASAT 36° East – here too many receivers will try in vain to lock in a signal.

As you can see there are many ways for TV stations to restrict feed reception for Joe Average even without resorting to encryption. However, if you’re in the know you can react accordingly and use suitable hardware to have your way in the end. In all TELE-satellite reports you will find some reference to a receiver’s SCPC capabilities and an account of how sensitively its tuner deals with weak sig-nals.

Diego rosende from tenerife, Spain

ron roessl from New York, uSa

Satheesan Puzhakkara from thiruvananthapuram, India

Documents

Making life hard for DXers – or: tV stations’ little ...tele-audiovision.com/TELE-satellite-1209/eng/feature-transmission.pdfMPeG 4:2:2 feed from the German parliament. a standard