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Many analog terrestrial radio and tv transmitters have been replaced by digital ones like DTT and DRM technologies. Analog radio signals include FM, MW and even SW. Although the quality of reception of the digital technology far outweigh the analog ones, analog based receivers are far cheaper and suitable for developing countries.

Due to DVB standard compliance including forward error correction implementation, digital radio and DTT receivers are still not a cup of tea for most people. For people living in developing countries, OTT is still not a viable option for the mass either as streaming cost data.

Terrestrial antennas have omni directional signal patterns, but such a proposed satellite base antenna can be directionally polarized reducing the huge power requirement. A broadcaster can feed data to the satellite based analog transmitter through Starlink.

Can a LEO based satellite constellation revive the analog radio or TV era? Is it even practicable?

seccpur
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  • That almost sounds like streaming video via Starlink! Too much power would be required at the frequencies used for analog television channels. – fred_dot_u Jun 05 '21 at 00:54
  • Interesting question! I'm not sure digital TV demodulation is more expensive than analog any more. Digital radios are central to cell phones and GPS chips for example, and can have bandwidths of MHz to tens of MHz. They are mass-produce and therefore cheap. The cheapest way to build a receiver for analog transmission would probably be to implement it digitally as well. With DSP and FPG implementations of signal processing, cost will be low. What's expensive is the giant screens necessary to take full advantage of DTV's potential. – uhoh Jun 05 '21 at 00:58
  • So a small box that picks up TV from the sky or the ground and feeds it to a phone (which many folks in rural areas, and third-world settings have (often even before access to safe drinking water) will be the way to to. I think that's a lot cheaper than them buying dedicated TV sets. Use whatever screen device they already have. – uhoh Jun 05 '21 at 01:00
  • Digital receiver uses digital modulation and error correction techniques that complicates the receiver hardware and makes it much costlier. Streaming cost data hence not suitable for wide audience. – seccpur Jun 05 '21 at 01:13
  • @fred_dot_u: Sounds logical, the power requirement will be more, but is it practicable at the first place. – seccpur Jun 05 '21 at 01:16
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    If you wanted to revive analog radio and television, on what frequencies would such transmissions be broadcast? In some countries, when the analog radio and television services was abandoned in favor of digital services, the radio frequencies used for the analog services, particularly those used for analog television broadcasting were sold by the governments to telecommunication companies to so they could be used for mobile/cellular telephone networks. – Fred Jun 05 '21 at 08:30
  • "Not that you would, but you could" digital is far more noise-resistant at far lower power levels. – Carl Witthoft Jun 05 '21 at 13:58
  • I am not focusing on the spectrum for radio broadcast nor the cost comparison of receivers. GEO sat is the choice for communication but LEO sat constellation will persistence of signal as well as distance from Tx to Rx within the reach of analog radio Tx. A 10 KW TV signal has about 60 KM radial coverage. – seccpur Jun 05 '21 at 14:34
  • @seccpur, if you are not thinking about cost of receivers, then you should consider removing the "suitable to for developing countries" in your statement of problem. – Ng Ph Jun 05 '21 at 17:33

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In the current state of technology, the answer is definitely no: analog transmission of TV and radio will not make the receivers cheaper.

First, this is because the receiver's antenna cannot be omnidirectional. It would pick-up too many signals from many satellites. A directional antenna that can track the wanted LEO satellite, then switch to another one when the current one disappears over the horizon would be expensive (its cost represents the majority of the cost of a Starlink terminal).

Second, you cannot reuse traditional AM/FM-receivers because of the high and varying Doppler effect. A new technology has to be developped.

uhoh
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Ng Ph
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    Not convinced any of this is true (other than cost). Modern heterodyne FM receivers track signal drift once locked on, for example. For sufficient $$ you could build one with much wider tracking capability – Carl Witthoft Jun 05 '21 at 14:00
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    @CarlWithhoft, I think money is a constraint in the developing countries for which the OP is considering the analog revival ;-) –  Jun 05 '21 at 16:26
  • If cost is not a KPI (key performance index), I wonder what else could be cited for arguing for analog transmissions? In fact, the LEO factor seems irrelevant in the debate on whether there is a sweet spot for analog vs digital transmission of information. – Ng Ph Jun 05 '21 at 17:38
  • For example GPS antennas are omnidirectional and pick up signals from a dozen or more at the same time. All GPS satellites transmit in exactly the same frequency band and correlators are used to pick out individual signals. Since TV signals pass through the ionosphere, it's not likely that there are lots of satellites transmitting towards the ground in TV bands. – uhoh Jun 05 '21 at 22:52
  • Thus "It would pick-up too many signals from many satellites" is unlikely to be at all true. This is unsupported and unlikely conjecture, can you add supporting links or sources? – uhoh Jun 05 '21 at 22:53
  • @uhoh, I assume that you are familiar with the Starlink constellation? You must then know that the Starlink terminal must select the best satellite from many that it can see in the sky at >40° elevation. A terminal without directional antenna will see many more satellites, by design. For a broadcast service, the geometry of LEO constellation constitutes a challenge. In fact, do you know of any broadcast service via LEO/MEO? – Ng Ph Jun 06 '21 at 12:04
  • @NgPh the question is about possibility, not economic viability. Starlink has to make money soon while simultaneously delivering low latency, high bandwidth to high latitudes. Question does not cover economic viability and asks about equatorial customers, with a lower analog TV bandwidth and no constraints on latency. Apples and oranges, one does not prove/disprove the other. It's not an easy question to answer, so broad, sweeping and unsupported generalizations won't do. – uhoh Jun 06 '21 at 12:20
  • @uhoh, "Although the quality of reception of the digital technology far outweigh the analog ones, analog based receivers are far cheaper and suitable for developing countries". If you remove the economic aspect, the question doesn't make sense (at least to me). I answered precisely this: why not take advantage of cheaper receiver accepting inferior transmission quality. One of my points is that, technically, the antenna system cannot be omnidirectional, and that will defeat the economic argument. Are you challenging this? – Ng Ph Jun 06 '21 at 13:17
  • @NgPh as long as questions are clear and answerable, they don't have to make sense; they are simply questions. We are invited to answer them or not answer them. I've added an answer now. Certainly nobody would try this but it at least addresses the question quantitatively. – uhoh Jun 06 '21 at 15:15
  • @uhoh, the question is clear (to me). Only when you decide to obfuscate the economical aspect that it doesn't make sense any more. In your Answer, you stated that LEO has the potential to revive analog transmission. For the sake of argumentation, let's ignore the economics (either in the cost of receivers or the cost of the space segment), let's say for a public service a country doesn't care about cost, would you advise that country to "revive" analog? – Ng Ph Jun 06 '21 at 18:30
  • @NgPh no I wouldn't! So reviving one analog FM radio frequency is in fact doable but if you are looking to get rich quick it's not going to work that well. +1 For making me think so hard! – uhoh Jun 06 '21 at 23:04
  • @uhoh, It's good that we stimulate each other intellectually. Can we converge to the following conclusion: It's doable, but people/governments would not do it for economic reasons? – Ng Ph Jun 07 '21 at 08:58
  • @NgPh Yes I think we can! It's conceivably doable, it's not impossible, but it seems like a very bad, awful idea given current satellite technology. :-) – uhoh Jun 07 '21 at 17:54
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Can a LEO based satellite constellation revive the analog radio or TV era?

Yes, potentially.

Is it even practicable?

No, not in the least, at least not for TV. For FM radio you might get one channel working with 100 satellites at 2,000 km and 4 kW each.

Per Prediction of the ‘useable’ coverage of FM radio services an FM radio with a rod antenna will receive STEREO FM at a power level of about -75 dBm which is about 3E-11 Watts. The rod antenna is shorter than a wavelength but will be part of a resonant LC tank circuit so their receive cross-section will be of order one square wavelength. Let's call it a third of that, or only 3 m^2.

Prediction of the ‘useable’ coverage of FM radio services

note: FM radio rod antennas are not really directional. If you point them vertically they won't receive from the zenith but they will from the sides. So our satellites will be using broad inclined beams to the front, back and side, and skip the nadir so as to best excite the vertical rod antennas.

So we need 1E-11 W/m^2 over a strip of land that's say 10,000 x 40,000 km^2 or 4E+14 m^2 or a total of only 4000 Watts if you could spread it evenly!

That sounds amazing, but it seems to be back-of-the-envelopish, spherical cowish true.

But let's throw in a factor of 100 for fun and say there are one hundred satellites in a low-inclination multi-plane constellation at an altitude of say 2000 km. This old SpaceX Starlink plot (back when they were thinking of higher orbits, from SpaceX's 4,425 satellite constellation - what's the method to the madness?) says for an altitude of 1000 km you have a useful radius of about 1000 km. We'll use the same triangle and say each satellite has a footprint of order) 2000^2 or 1.3E+07 km^2 which is 3% of our 10,000 x 40,000 footprint.

So one hundred satellites of 4 kW FM broadcast, directed in annular or conical beam should be able to give fairly good FM reception to the developing world. It will not be excellent, there may be occasional dropouts (it may be more like listening to Short Wave than Sirius XM), but it certainly may work.

A 8 kW solar panel is nothing to shake a stick at (4 kW power, 50% of the time in eclipse), it's pretty big, like 25 m^2 roughly. And the antenna, while mostly very light weight dipoles, will be nontrivial in size. But it will be a lot smaller than the one discussed in answers to Why do AST SpaceMobile satellites have antennas much larger than Starlink, whereas they both aim at providing network coverage anywhere on earth?

So reviving one analog FM radio frequency is in fact doable but if you are looking to get rich quick it's not going to work that well.

method to the madness

Source: old SpaceX FCC filing, from SpaceX's 4,425 satellite constellation - what's the method to the madness?

uhoh
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  • This reasoning seems to assume that the satellites do not move. However, as they are not GEO, they do move (very fast indeed, ~7Km/sec for sat at H=2000Km). To continue with the back-of-envelope calculation approach above, if the coverage is a (flat) circle of R=2000Km, the fly time over he coverage is about 9.5mn, in the best configuration. For a broadcast service, receivers must be able to frequently switch satellites (and frequency) to provide continuity of programme. – Ng Ph Jun 06 '21 at 17:20
  • "A strip of land 10,000x40,000Km²..."(?) The total land mass of Earth is ~ 150 Million Km²! – Ng Ph Jun 06 '21 at 17:26
  • @NgPh There is a challenge in the overlap region but it's not as bad as you think. This is FM radio and FM radios use phase-locked loops to receive. It will lock on to the strongest carrier frequency within it's bandpass. As long as the carriers are offset a small amount, ~ a few kHz, they will not be confused. While a vintage 9 transistor AM/FM radio may not have a PLL, anything with a chip in it will. FM is amazingly good at rejecting all but the strongest signal. There's a long and sad story about its invention and delayed adoption. – uhoh Jun 06 '21 at 22:58
  • @NgPh ...of FM radio. (Edwin Howard Armstrong) I've drawn a spherical cow on the flat back of an envelope for an order of magnitude calculation. All arguments or nit-picks smaller than a factor of 10 are hereby summarily dismissed :-) – uhoh Jun 06 '21 at 23:00
  • so in your strawman system, the LEO speed effect on FM radio would be like the one we experience while driving long-distance, occasionally leaving one coverage area and moving into another one. Except, that the frequency of drops would be higher (the 9.5mn is the ideal configuration), more irregular and less intuitive. I take note that you assume each satellite will have a distinct frequency (although they broadcast the same content). – Ng Ph Jun 07 '21 at 08:45
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    I am a retired and lazy engineer, so I am a fan of back-of-envelope approaches. That what I told my young engineers, an engineer who is confident of himself must master the art of approximative computations. – Ng Ph Jun 07 '21 at 08:49
  • @NgPh I proposed that the carrier frequency be shifted by only a few kHz, but the bandwidth of a stereo FM signal is roughly 75 kHz! So it's not exactly "different frequencies", you wouldn't touch the knob or need to fine tune, it's just a simple trick to help the FM radio distinguish between different satellites. If you're listening to 101.5 FM it doesn't matter if it's 101.505 or 101.495 MHz. You can see the FM signal makeup here and here for example. – uhoh Jun 07 '21 at 18:02
  • I am lost. First, I assume that the 75kHz is the frequency deviation and not the bandwidth (cf Carlson rule). If 2 satellites (say one setting while the other is rising above the horizon) can transmit FM radio at carriers close by kHz, why do we have the often quoted 200kHz channel spacing (for +/-75kHz deviation)? Sorry, FM planning is such a fainting memory for me. – Ng Ph Jun 07 '21 at 20:39
  • @NgPh The 200 kHz spacing allows the listener to hear the weaker station by tuning to a different channel. If there's a strong signal and a weak signal (e.g. the towers are 0.5 km and 50 km away) the listener can easily hear either one they want by tuning from one to the other, and the stronger does not interfere with reception of the weaker. Here it is just the opposite; we want the stronger signal to BLOCK the weaker one. We WANT interference. – uhoh Jun 07 '21 at 22:33
  • "We WANT interference" (?). FM modulation cannot do that trick. If you are referring implicitly to the "capture effect" of FM, beware that there is no "blocking" (=zeroing) of the weaker signal. It makes its output looks like random noise so your ear cannot hear it (as voice or music). But your overall quality (S/N) will be degraded. You can take advantage of the FM capture effect in some special applications (eg wireless MIC), but not in high-quality strereo sound. Otherwise the ITU-R is all wrong in its recommendation on protection ratios Rec (cf ITU-R BS 412-9, 1998). – Ng Ph Jun 09 '21 at 18:10
  • My memory is coming back. The 200kHz is channelization (not spacing). FM stations that transmit several carriers space them at nx200kHz, n>=2. In frequency congested areas, most likely n=2. Check where you live whether this is true (your broadcasting authority must have a list of authorized stations and the frequencies allocated to each). – Ng Ph Jun 09 '21 at 18:21
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FM radio (at near 100MHz carrier) is pretty much local (the visible horizon is almost the limit). It is up to local authorities to allow FM analog broadcasting in the 88-108MHz band and up to local businesses to find a viable business model, no space technology needed. A few kW transmitter is damn cheap and works flawlessly.

My country (Bulgaria), while not really 3rd world, delayed its transition to digital radio for a variety of reasons, to the point it became pointless - both established FM radio stations and startups emerged online, mobile Internet connection is acceptably cheap and everyone has it on their phone. The transition to digital radio is expensive and no one sees any point for paying it up.

That's why we still listen to analog FM radio - including 2 government-controlled and quite a few private stations.

If one wants to establish a new station, they can get an FM frequency pretty cheap. And no one bothers anymore.

In short, FM radio is alive and kicking without any rocket science involved.

What about the analog TV? Well, we somehow succeeded in the transition from analog to digital TV. The TV band is already re-occupied by the digital broadcast. You are not allowed to broadcast analog TV anymore - no matter if you do that from a satellite.

And even if we talk about a country where digital TV is not on the table, your potential auditory will need to find analog-TV receivers.

And the usual kind of sat-tv is pretty much popular exactly in the developing countries. So no business model either.

MW and SW: they don't really play well with space.

First, one needs pretty much large antennas for them (not suitable for a satellite). How about 50m for a simple dipole?

And second, the same ionosphere that makes possible MW/SW reception over the horizon will make a Sat MW/SW quite a challenge.

A quick walk over the MW/SW band reveals a great deal of stations from all over the world alive and transmitting. These are alive as well and the space offers no possible improvement.

The peculiarities of the MW/SW bands makes them safe against any attempt of digitalization.

fraxinus
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  • I agree FM TX are still in vogue but rugged terrains and high-rise buildings can be create shadow regions, there terrestrial tx signals range are limited in such areas. – seccpur Jun 06 '21 at 16:40
  • @seccpur this is nothing new in FM world and the space will rather not solve much of it. – fraxinus Jun 06 '21 at 16:44
  • @fraxinus, Good observation (FM radio is not dead). One reason why, compared to TV-broadcast (not only in Bulgaria) is because it occupies only 20-MHz spectrum. Let's not forget that the real benefit of digitalisation is spectrum efficiency, which for TV broadcast (UHF) served the purpose of allocating more spectrum to the powerful mobile telephony companies. Coming back to the original question of "reviving" (something which is dead or in terminal state), eg FMTV, I don't see any potential reason, whether technical, economical or institutional, from LEO infrastructure (or else). – Ng Ph Jun 06 '21 at 20:31
  • Of course things like images (facsimile via radio or "radiofax" is quite old and was a critical tool in data transmission historically, and is at least arguably a digital modulation scheme transmitting 1's and 0's in the HF band. https://en.wikipedia.org/wiki/File:Krant_per_fax_-Faxed_newspaper(4193509648).jpg and these days amateur radio operators still use morse code and some other digital modulation schemes in the HF bands, but ham radio is not commercial radio. – uhoh Jun 06 '21 at 23:17
  • I now realize the somewhat hidden rationale of seccpur. The potential advantage of LEO is high-elevation geometry. As pointed out by fraxinus, ionospheric fading will play against FM radio and FMTV (if we remain in VHF/UHF). What you gain by avoiding shadowing and blocking, you will pay back in terms of scintillations fadings. Moving to higher bands to avoid ionospheric impacts? You will pay in space loss, inter-systems interferences (and run the risk of being in the radar of the mobile operators). – Ng Ph Jun 07 '21 at 12:57