Satellites : general discussion and musings

[whatsgoingon]

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[whatsgoingon]

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[Dmitry]

However, as the angle of incidence for the radio wave is increased, the wave enters the ionosphere at an ever more oblique angle, and the Maximum Usable Frequency goes up and up! Right up to 10GHz (thats 10 GIGA Hertz) and beyond!

Oh, really? Any technical data?

In WWII, the practical application of Ionospheric Radiowave Propagation theory was taught to US military personnel over a fortnight in a very short course:

From: http://tf.boulder.nist.gov/general/pdf/2402.pdf

... The first handbook, "Radio Transmission Handbook Frequencies 1000 to 30,000 kc.," was issued in January, 1942, giving the basic principles of radio sky-wave propagation, and such computational procedures as were extant at that time, together with preliminary versions of prediction charts and predictions for the winter. A supplement to this handbook was issued June 1, 1942, which gave summer predictions.

Even if it was issued in December 1941, "kc" stands for "kilo-cycles" (per second), to "1000 to 30,000 kc." = "1 .. 30 MHz". Right the same LUF..MUF range (by order of value).

[Dmitry]

You really helped make your point. Higher bandwidth signals (2-10 Ghz) are able to be bounced locally. I never argued Africa. Thanks for your insights as always.

Excactly, whatsgoingon, locally. At 300 km or less.The range of "2-10 GHz" in not used for satellite TV. Ku band for Europe is 10.7-12.75 GHz.

Now try please to explain why the dish elevation angle varies from 30.9° for London to 45.2° for Sevillle and Catania as it is sown in http://www.europarl.europa.eu/eplive/ex ... ide_EN.pdf, page 11, and lines with constant angles are so round. How could it work without a transmitter high above the equator? With thousands of ground transmitting antennas in Europe?

[whatsgoingon]

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[whatsgoingon]

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[simonshack]

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Allow me to submit a few basic, layman's musings in this thread titled: "Satellites : general discussion and musings".

Firstly, I was wondering why the whole of Europe has - in later years - switched to the so-called Digital Terrestrial TV broadcasting system. In Italy for instance (and I believe in other countries too) it has turned out to be a total, unnerving disaster in terms of TV signal stability/ reliability (there is an uproar about this here - and my neighbors and friends all have lamented dire problems with it - such as constant image disturbance/ random image-freezing / and outright signal blackouts). In fact, here's an article about this in the Italian mainstream newspaper "La Repubblica":

TV, IL DIGITALE DISTURBATO
Schermi neri e voci spezzate - Il digitale peggio delle vecchie tv

translation: " TV, THE DISTURBED DIGITAL - Black screens and jagged audio - digital worse than the good'ol TV"


http://inchieste.repubblica.it/it/repub ... 1570640%2F

Now, Wonkypedia describes it as a "technological evolution" - a claim my neighbors & friends would bitterly LOL at!

DIGITAL TERRESTRIAL TELEVISION
Digital terrestrial television (DTTV or DTT) is the technological evolution of broadcast television and an advancement of analog television. DTTV broadcasts land-based (terrestrial) signals. The purposes of digital terrestrial television, similar to digital versus analog in other platforms such as cable, satellite, and telecommunications, reduced use of spectrum and to provide more capacity than analog, provide better quality picture, and to lower operating costs for broadcast and transmission (after the initial upgrade costs).
http://en.wikipedia.org/wiki/Digital_te ... television

In fact, as that Repubblica article mentions, it seems that TV technology has "gone backwards"... Here's my best translation of a key paragraph of that article: "It was meant to be a revolution for all TV viewers, instead it seems that we have gone back in time. Four years after the first switch-off [of the analog system] in many parts of Italy it is still impossible to receive some channels." And we are talking here about some MAINSTREAM state-owned and Berlusconi-owned channels which Italians have grown addicted to - not about those tiny, commercial channels which sell kitchen-ware or fitness machines!

Well, what exactly is going on here? Why do even these mainstream channels go along with losing huge chunks of their viewership - for as long as four years? What exactly was the reason for switching to "Digital Terrestrial"?

So I decided to look up what the EUROPEAN BROADCASTING UNION's has to say about this. I found this technically loaded pdf file - which I hope our members "whatsgoingon" and "Reichstag Fireman" will help me decipher:

http://www.etsi.org/deliver/etsi_en/300 ... 10102p.pdf

I will just highlight here an interesting paragraph and an interesting graphic - extracted from that pdf file :



INTERESTING PARAGRAPH:

Scope
The present document describes the modulation and channel coding system (denoted the "System" for the purposes of the present document) for satellite digital multi-programme Television (TV)/High Definition Television (HDTV)
services to be used for primary and secondary distribution in Fixed Satellite Service (FSS) and Broadcast Satellite
Service (BSS) bands. The System is intended to provide Direct-To-Home (DTH) services for consumer Integrated
Receiver Decoder (IRD), as well as collective antenna systems (Satellite Master Antenna Television (SMATV)) and
cable television head-end stations, with a likelihood of remodulation, see EN 300 429 (bibliography).

INTERESTING GRAPHIC:

I certainly do not pretend to understand all the technicalities involved here - so what I'm doing here is just asking for help!

[whatsgoingon]

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[reichstag fireman]

Just want to point out a mis-use of terminology here.

Bandwidth is a measure of the theoretical raw capacity of a transmission channel. It is not the same as the carrier frequency that a radio signal is actually transmitted on.

For example, AM commercial radio stations in the USA are broadcast in the "medium wave" band on carrier frequencies between 540kHz - 1610kHz. However, the channel bandwidth of an AM radio station in the USA is just 10kHz. Hence the awful sound quality.

And for FM, in the EU/USA commercial FM broadcast stations transmit on frequencies in the "VHF" band between 88MHz and 108MHz. BBC Radio 1 FM is broadcast on frequency 98.5MHz from the Crystal Palace transmitter in London. However, the bandwidth allocated for the station's audio signal is 53kHz. Plus a few more kHz in bandwidth to carry the station's digital RDS / RBDS data, etc.

In the case of a "satellite" (skywave) broadcast in the "Ku-band", transmitted on a microwave frequency of ~10GHz - 12GHz, the transponder (just a signal multiplexer) has a channel bandwidth of a few tens of MHz. In the case of "ASTRA/SES" and its "transponders" used to refract the BSkyB TV channels into the UK, the bandwidth of a "transponder" (aka multiplexer) is 33MHz.

Without getting into the complexities (Shannon-Hartley et al), channel bandwidth should be used as efficiently as possible. The transmission channel should also be reliable in the presence of noise. That requires an efficient modulation scheme at the physical layer (4-QAM/QPSK), an efficient transport layer and mux-demux system, and an efficient (if lossy) data compression scheme - mpeg2 for DVB-S - "standard definition satellite TV", and mpeg4 for DVB-S2 - "high definition satellite TV".

So channel bandwidth is not the same as the carrier frequency of a radio signal.

[reichstag fireman]

However, as the angle of incidence for the radio wave is increased, the wave enters the ionosphere at an ever more oblique angle, and the Maximum Usable Frequency goes up and up! Right up to 10GHz (thats 10 GIGA Hertz) and beyond!

Oh, really? Any technical data?

Breit & Tuve 1926? Appleton 1932? IRPL 1943?
All referenced further up the thread.

In WWII, the practical application of Ionospheric Radiowave Propagation theory was taught to US military personnel over a fortnight in a very short course:

From: http://tf.boulder.nist.gov/general/pdf/2402.pdf

... The first handbook, "Radio Transmission Handbook Frequencies 1000 to 30,000 kc.," was issued in January, 1942, giving the basic principles of radio sky-wave propagation, and such computational procedures as were extant at that time, together with preliminary versions of prediction charts and predictions for the winter. A supplement to this handbook was issued June 1, 1942, which gave summer predictions.

Even if it was issued in December 1941, "kc" stands for "kilo-cycles" (per second), to "1000 to 30,000 kc." = "1 .. 30 MHz". Right the same LUF..MUF range (by order of value).

Yup.. and in the 1940s, skywave was used for (analog) voiceband, and CW (morse code). Very small channel bandwidth demands. In the case of voiceband, maybe 20kHz at most. So no need for UHF and microwave frequencies.

We could look at this from multiple perspectives..

In the UK in the 1970/80s, analog terrestrial TV shifted from a VHF band to UHF. Why? Because there was a need for more channel bandwidth. The widespread availability of colour TV and a move from 405 to 625 raster lines for "high resolution" required more bandwidth. The signal couldn't easily be modulated on a VHF frequency, so analog TV broadcasts were moved to UHF, which is where they are today..

Although today's digital terrestrial TV (DVB-T/2) is transmitted at an even higher frequency (~700MHz) than the analog TV (~500MHz) it replaced. And there are even greater bandwidth requirements for the DVB-T2 multiplexes (Muxes). Around 8MHz bandwidth per DVB-T2 Mux is needed which use 64-QAM modulation. Each Mux provides a datastream of 40Mbps, for transmitting three or four HD TV channels with mpeg4 encoding, or even ten or twelve TV channels in "standard definition".

Amazing really. Just a shame the technology is wasted transmitting the sewerhole output from the BBC, SKY, et al !

So going back to 1943.. why didn't they use skywave at microwave frequencies back then? Because they didn't need it. In those pre-digital days, they had very limited bandwidth requirements. Just voice and morse code. And that explains why the IRPL Radio Propagation Handbook, published 1943, does not mention skywave propagation at microwave frequencies.

Even if microwave-based skywave systems were technically possible(?) back in the 1940s, they would have been too costly and complicated to implement compared to skywave systems transmitting on shortwave. So they stuck with shortwave. We are talking about 70 years ago. They hadn't even 'split the atom' back then

However the theory and the application detailed in that Handbook - Snell's Law of Refraction, ionospheric electron density and the Appleton-Hartree Equation - are nevertheless just as relevant to today. Whether at shortwave frequencies or in the high-bandwidth microwave skywave systems which are operated today under the guise of "geostationary satellites".

[reichstag fireman]

*Well, what exactly is going on here? Why do even these mainstream channels go along with losing huge chunks of their viewership - for as long as four years? What exactly was the reason for switching to "Digital Terrestrial"?

In the UK, prior to the "digital switchover" with analog TV we were 'limited' to just four or five stations (of which three are state-owned/funded - BBC1,BBC2,C4). It was claimed we had to Go Digital to more efficiently use the limited RF spectrum available, to make room for more TV stations. The channel width (bandwidth) needed to transmit an analog TV signal is many times more than the bandwidth needed for a digitally modulated (and digitally compressed) TV signal.

So along came DVB-T (digital terrestrial TV) and it became possible to pack ten or twenty stations into the same space in the RF spectrum as a single analog TV station. And bandwidth can be allocated dynamically. There are now a handful of high bitrate (~10Mbps) TV stations broadcast on DVB-T2 in "high definition". These are actually higher definition than DVB-S2 - the equivalent on the "satellite" TV platform. But with a higher order modulation scheme (64-QAM), the HD stations require an even higher signal-noise ratio (SNR).

The big problem with digital TV (groundwave or skywave) is that it does not "degrade gracefully". Glitching from channel noise on a critical component of the signal, e.g. corruption to the keyframe in mpeg2, totally ruins the 'viewing experience'. Whereas in the old days of analog TV we somehow learned to ignore the various video artifacts - ghosting (signal aliasing), snow (channel noise), etc.

The migration to DVB-T does however make it easier for them to rollout subscription channels (i.e. porn), since the decryption process is much simpler to implement, being based on a trivial manipulation of the digital bitstream.

So perhaps the simple explanation for the migration to digital TV is the greed of broadcasters.

One point perhaps worth noting is that DVB-S "satellite" TV does not suffer from a phenomenon known as "multi-path fading" (MPF). This is a common problem for signal comms based on groundwave propagation, e.g. DVB-T.

MPF is caused by signal reflections from obstacles in the path of the wave - e.g. hills, mountains, trees, buildings. Every reflection creates a new signal path from TX to RX. And each of those multiple paths from TX to RX is slightly different in length. So multiple copies of the original signal arrive at the receiver, all slightly out of phase. The receiver sees this as noise, and it is more difficult to recover the original (correct phase) signal. That is a common cause of audio/video glitches. With line-of-sight "satellite" (skywave) broadcast systems there just isn't the problem of multi-path fading.

So I decided to look up what the EUROPEAN BROADCASTING UNION's has to say about this. I found this technically loaded pdf file - which I hope our members "whatsgoingon" and "Reichstag Fireman" will help me decipher:

http://www.etsi.org/deliver/etsi_en/300 ... 10102p.pdf

I will just highlight here an interesting paragraph and an interesting graphic - extracted from that pdf file :

INTERESTING PARAGRAPH:

Scope
The present document describes the modulation and channel coding system (denoted the "System" for the purposes of the present document) for satellite digital multi-programme Television (TV)/High Definition Television (HDTV)
services to be used for primary and secondary distribution in Fixed Satellite Service (FSS) and Broadcast Satellite
Service (BSS) bands. The System is intended to provide Direct-To-Home (DTH) services for consumer Integrated
Receiver Decoder (IRD), as well as collective antenna systems (Satellite Master Antenna Television (SMATV)) and
cable television head-end stations, with a likelihood of remodulation, see EN 300 429 (bibliography).

INTERESTING GRAPHIC:

I certainly do not pretend to understand all the technicalities involved here - so what I'm doing here is just asking for help!

Thank you! Interesting. Needs proper study - not immediately sure what it answers about the 'question at hand' !

[Dmitry]

You really helped make your point. Higher bandwidth signals (2-10 Ghz) are able to be bounced locally. I never argued Africa. Thanks for your insights as always.

Excactly, whatsgoingon, locally. At 300 km or less.The range of "2-10 GHz" in not used for satellite TV. Ku band for Europe is 10.7-12.75 GHz.

Now try please to explain why the dish elevation angle varies from 30.9° for London to 45.2° for Sevillle and Catania as it is sown in http://www.europarl.europa.eu/eplive/ex ... ide_EN.pdf, page 11, and lines with constant angles are so round. How could it work without a transmitter high above the equator? With thousands of ground transmitting antennas in Europe?

Wait. Prove Satellites exist. How'd they get up there. Show me a single convincing rocket launch. Sure we can imagine your line-of-sight communications to the Satellite belt on the equator, but then what logical argument proves the existence of satellites. As far as I can tell, for more than a year now. There is nothing but bad photoshops and a couple of NASA jocks doing a few trig functions on here. So this leaves me feeling a little less sure of your technology being anything more than simple ground stations.

What ya trying to hide?

For all we know the equatorial longitudes for these things are the skywave reflection points. Why would that surprise me at all.

Your move. Prove the shiny metal objects exist in the first place.

Suppose you're a lone shepherd living high in mountains. The nearest road ends 100 km far and 2 km lower to your home. One day it happens to me to tell you about cars. You claim that I'm fool and that I must carry one to you to make you believe. You know... I will not. I have nothing to hide, but I simply will not carry tonnes of metal on by back just to hear that combustion engine is fake and the real source of all noise and smoke is Satan.

1. Skywaves do exist.
2. Skywaves were and are used to transfer some signals.
3. Skywaves were and are explored. Legally. Related scientific and technical data are not secret.
4. Receiving 10-12 GHz waves with a parabolic dish mounted at Sicily with the elevation angle of 45° can not be explained as sky wave propagation. The atmosphere can not redirect such signal this way. It can be flying spaghetti monster, but not atmosphere.

[Dmitry]

So as RF is saying, grazing angles, like q = 89.9 degrees makes 1/ cos(q) go to large coefficients making GHz reflections possible. You then get higher electron density on the equator.

But it is short-sighted of you to dismiss the possibility, no?

Suppose the reflection of 10 GHz is possible if you emit it with q = 89.99.....9. This is to say, if it's horizontal.

Can this signal be caught by a dish inclined at 69° to the horizon? (Bogota, http://nhkworldpremium.com/apply/equip_e.aspx?ssl=false)

[Dmitry]

However, as the angle of incidence for the radio wave is increased, the wave enters the ionosphere at an ever more oblique angle, and the Maximum Usable Frequency goes up and up! Right up to 10GHz (thats 10 GIGA Hertz) and beyond!

Oh, really? Any technical data?

Breit & Tuve 1926? Appleton 1932? IRPL 1943?
All referenced further up the thread.

Breit & Tuve emitted 10 GHz waves back in 1926? Or was it Appleton 1932? There are many (completely pointless) references up in this thread, but my be you can give only 4 short entries:

* source (the precise page and paragraph);
* frequency (carrier), in GHz;
* distance, in km;
* receiver elevation angle, in degrees.

Not Jules Verne style belletristic, only 4 short lines please.

[Dmitry]

The migration to DVB-T does however make it easier for them to rollout subscription channels (i.e. porn), since the decryption process is much simpler to implement, being based on a trivial manipulation of the digital bitstream.

So perhaps the simple explanation for the migration to digital TV is the greed of broadcasters.

I agree at 100% with this point. In Russia, the same thing is done even simpler and cheaper, without nation wide digitalization. By simply lowering the quality of freely available signal while aggressively marketing cables/dishes.