# Radio technology: Receiving without the ability to transmit

Scenario: In my alternate-Earth scenario, Europeans did not colonize the Americas. They use navigation only to circumnavigate Africa and go to India. Maybe they know there is something to the West, but they don't want to go there for some reason. Anyway, science keeps progressing and they discover the Radio technology.

Problem: I would like the Europeans to discover the Radio and transmit information to the American civilizations, but only as a one-way transmission. In other words, the Americans are able to receive the radio transmissions, but they are not able to transmit it themselves.

This is important in my scenario, because I want the Americans to learn the English language (or equivalent 'franca' language) without the need to both civilizations get directly in touch. Probably other civilizations will benefit from it (Indians, Chinese), but in this case they have an established relationship with the Europeans, which the Americans don't have.

Question: How is it possible to capture long distance radio transmissions without the ability to transmit it back? Is it feasible? I would like to keep this scenario for 10-20 years.

• Yes, if you don't have power amplifiers. Which seems very unlikely. – Karl Aug 23 '18 at 18:45
• In real life, it is a very plausible scenario that you have a receiver but no transmitter. But as far as inventions go, it would be as unlikely as having baseball gloves without the any kind of balls. – Alexander Aug 23 '18 at 18:49
• I'm a little confused by your wording here. Are you describing a scenario where the Europeans are transmitting information to the Americas ON PURPOSE, or the Europeans are just talking amongst themselves, and the Americans are listening in? – Morris The Cat Aug 23 '18 at 19:04
• Learning a language is highly unlikely with just spoken words without context. A better scenario would be to have a lone European wash up on shore to teach them the language. He was lost in a storm and thus the Americas were not 'discovered' yet. He might have had a crude 'fox hole radio' as one person noted but not know how or why it worked and thus would not be able to build a transmitter. – Tracy Cramer Aug 23 '18 at 20:25
• @MatthieuM., they're trying to broadcast to India.... That isn't the Q's intrisic problem. The real problem is that technological development is interconnected. It's a hard nut to swallow that anyone would develop a radio receiver without wanting to transmit in the first place. The behind-the-tech-curve weak transmission power of Cort Ammon's answer is the best answer. – JBH Aug 24 '18 at 16:41

I actually think it IS feasible. Very much so. Your Native Americans would just have to build a radio receiver while intending to build something ELSE.

It's not all that unreasonable to propose that as materials technology developed in the Americas, they eventually began using more sophisticated metals in the construction of their buildings and religious objects. Imaging if they've been building a particular religious object out of copper and various other things that essentially makes it a radio reciever, and one day they build one that just HAPPENS to be the right size and shape to capture the frequency of the European transmissions?

They'd be almost certain to interpret this as hearing the voices of gods, and while they might devote a lot of time to trying to interpret those words, they'd be starting from absolute scratch in terms of trying to figure out how to talk BACK.

I mean... it worked with Lucille Ball's TEETH, so...

• Without amplification at the receiver, it is unlikely in the extreme that AM broadcasts could be detected across the Atlantic. – Martin James Aug 23 '18 at 20:55
• Even if the radio was actually built and the signal was picked up correctly (both unlikely because you need to guess the frequency just right), where would the sound output come from? It's not like they're going to have loud speakers or earphones. – ChatterOne Aug 24 '18 at 8:31
• @ChatterOne In addition to the copper wire coils, their Religious Totem also contains a crystal – Chronocidal Aug 24 '18 at 13:23
• @Chronocidal If you read the link that you provided you'll see that it also needs An earphone to convert the audio signal to sound waves so they can be heard. The low power produced by a crystal receiver is insufficient to power a loudspeaker, hence earphones are used. So even with a crystal, no earphone, no party. – ChatterOne Aug 24 '18 at 13:25
• @Chronocidal That is still a stretch at best. You'd need a crystal that has to be the right type, connected to an antenna, a coil of wire and a capacitor (and they should build the capacitor, too). All of this should be tuned to a frequency that you don't know, be able to somehow pick it up from 10-12.000 km away and connected to another crystal that will act as a piezo tweeter. One heck of a coincidence for something that they built only as a totem. – ChatterOne Aug 24 '18 at 13:41

The answer is to limit transmit power, but there's some real questions as to the feasibility of this as an approach to learn a language.

The simple answer is that the Americas have radio, but not large power production systems. Consider that a small walkie talkie can operate on a pair of AAs, and a radio reciever can also operate on a pair of AAs. However, the radio station transmitters are measured in megawatts. If such localized power is simply not feasible with the way the American technology progressed, then they can't transmit. Perhaps their society valued efficiency over brute strength.

However, I do have to point out a major hurdle for your idea: the Americans probably can't learn English this way. You can't learn a language passively without some shared context. The only thing they could talk about is the weather, and for the most part the weather is very different half way across the globe. Perhaps the Americans might learn the words for the seasons, because both parties are in the northern hemisphere, but this would probably be the limit.

Consider if you had a message like this:

Uvtu cbjre trarengbef ner znpuvarf.

Now you've spent a great deal of time analyzing this langue. You understand the grammar petty well. You understand that if a sentence has the word "ner" in it, it describes something that has some transitive behaviors. You've seen "Znpuvarf ner gbbyf" and "znpuvarf" is on the right side of "ner" in our sentence, so you think it's highly likely that "Uvtu cbjre trarengbef ner gbbyf" would also be a true sentence. Unfortunately you don't have any context to know for sure.

But how could you possibly know that "znpuvarf" was the word the Europeans used for machines? You never got to see one, and you never got to ask the Europeans questions. You need something like the Rosetta Stone to stand a chance of getting the meanings right.

And I'm being kind here. The sentence structure I used for the language in this example is very similar to English. The meanings of the words are also similar. We don't have issues such as the Chinese word "Ch'i," which is brutal to try to capture in English.

In fact, all I did was rot13 encode English to create that language. If you knew English, and I gave you a large enough text, you'd have eventually realized that all I was doing was letter substititions. However, if you didn't already know English, it would have been inpenetrable.

Languages are designed to be used in a common context, such as face to face communication. It is, in fact, mathematically provable that you cannot determine whether a sentence is true or not by doing nothing more than listen to sentences.

It's not until you're face to face with your newfound friend, and someone does something terribly foolish in a cute sort of way, and that friend points and exclaims "baka!" that you stand a chance of understanding what "baka" means.

(In this case, "baka" is not rot13. It's actually a Japanese word which is terribly frustrating to try to properly translate into English. "Fool" is a decently close word, but it misses out on key nuances)

For a wonderful depiction of what happens when you lack proper context, I highly recommend the movie Galaxy Quest. In it, they have an alien species which passively observed our Star Trek like TV show, and then tried to interact with us based on those observations. Hilarity ensues, and they don't even try to approach this language question. It's the engineering that goes horribly wrong when they build their Star Trek like ship.

Edit Reading the comments has been fascinating. It appears this task is less clearly impossible than I had thought. HAM radio operators demonstrate the ability to connect across the globe with very low power, though such connections are spurious. This suggests that transmission may be possible, but they might not find it valuable because they can't control the environment enough to maintain a reliable connection to one individual over long periods.

The second interesting tidbit was finding out that AIs were having great success in identifying words which have the same semantic meaning in two language without an interactive back-and-forth pattern or parallel sentences. This would make it possible to identify, for instance, the word for "leaf" and "tree" by using their relationships.

I still believe the Native Americans here could not achieve this. At the very least, it would require a robust computer hardware production capability, which is at odds with the "low power" argument. However, it does show there's a sliver of hope. It's possible, though I'd still argue improbable.

• This. I also can't imagine a way one could learn a language by just hearing it spoken. Audio learning includes significant chunks of speech in a language you know in order to work. Imagine you know neither Italian nor French and stumble upon an audio tape of learning French for Italians. In this case you might reasonably deduce some words in both languages such as "Hello" or "Thank you" from their placement and intonation, but hardly anything much else. – Gnudiff Aug 24 '18 at 4:43
• Excellent answer. Let me give you one more thing to consider - In Polish there are often sentence where if it is a statement or a question depends on an intonation only. You can say Masz czas (You have time) with an intonation going down and say Masz czas? (Do you have time?) with an intonation going up or varying with an end going up. We're still in the same language family (Indo-European) as English (and most languages in Europe) and with just hearing those sentences you'd probably be lost in the grammar as well as the vocabulary. – Ister Aug 24 '18 at 8:16
• Another example - during WWII one of the Indian tribes was providing transmission encryption. All they were doing was translating the message to their native language. It was the best encryption used during the war, never even close to breaking it. You can imagine the same will happen in case of reversing which language you try to break/understand. – Ister Aug 24 '18 at 8:19
• @Gnudiff without knowing a languages grammar it's difficult to know even were simple words are placed in a sentence. Take the time 6.30 in English we describe it as half past six, German speaker says half before seven. There may be different grammatical conventions that cannot be understood purely by the audio. – Sarriesfan Aug 24 '18 at 9:50
• Your premise here is simply wrong. Radio transmitters for transatlantic operation need not be measured in megawatts - 100 watts is well more than needed, and under good conditions a watt or two will do. Try to develop the industry to manufacture tubes or semiconductors without being able to produce that much electrical power - not going to happen. Lack of RF power amplifiers would be vaguely feasible; lack of basic power supplies not. – Chris Stratton Aug 25 '18 at 1:46

There are other potential issues with your scenario, such as CrossRoads brings up in another answer. If I recall, the Germans actually tried to see if the English were using radar technology in World War 1, but they were not checking in the same band that the English were transmitting, so their engineers reported back that their enemies were not using radar technology yet.

But you suggest this is a modern (or at least closer to it) time and technology, so I will ignore the other issues for a moment and just assume that both sides have some radio capability and that they either randomly happen to be using the same frequency ranges or that they are tuning into ranges they've found each other to be using (like SETI searches/tunes to other stars looking for life)...

The answer to you question is that, yes, you can have the ability to receive without having the ability to transmit. There could be multiple reasons for that, and any 1 or more of them could be thwarting your Americans simultaneously.

• Transmitting takes more power. This is my favorite for you, as all you have to do is say that the Americans don't have the ability to transmit all the way across the ocean. That is easier than saying they cannot transmit at all.

• The signals can be highly directional. This is related to power, but it deserves its own mention. Maybe the Europeans figured out earlier how to send directional signals so that they could send at reduced power.

• Though the physics behind transmitting and receiving is similar, and you can use the same antenna to do both, the hardware to send and receive need not be the same. You can make one without having the other.

• Did the Americans even make it themselves? If you want to keep to history and say that the Europeans were technologically a bit more advanced, you could have the Americans find a European radio receiver washed up on shore.

• Maybe the Americans don't even have an electrical power source at all. Maybe they just stumbled onto a way to passively collect the signals and don't even understand how it works. Picture a cartoonish funny-looking huge receiver connected to the good old string and cup telephone method.

• The list could go on, but the point is yes, there are many ways that the Americans would be able to hear the European broadcasts but either not be able to broadcast back or at least not have the Europeans be able to receive the broadcasts back.

• Here is another possibly realistic one: the Americans have developed more sophisticated radio technology, but the Europeans have developed better power technology. This also helps with the "but they're probably not on the same channel" arguments. Let's say the Americans have developed radio technology that lets them scan and search for intelligent life on other planets continents, but their electrical power technology is much more limited. The Europeans have developed powerful batteries or other means of pumping a lot of power through their very limited radios. If the Americans transmit with very low power and/or Europeans have not developed good amplifiers, then in this scenario too you can get what you want. Though the Americans can probably transmit over very short distances in this one.

Another argument against the "they aren't going to be on the same frequency" challenge is this: we use very narrow frequency ranges for communications now, but that was not always the case. The ranges used to be a lot wider. Before techniques were developed for tuning into a specific frequency, receivers would be receiving across an entire large band. If the transmit and receive devices are both operating on very, very loose bands, the likelihood they will overlap is greatly increased. If they have the technology to limit themselves to narrow bands, then they probably also have the tech to scan over the band and look for communications.

OP did not specify what level of technology this is, only that there are radio communications. And OP should not need to specify that, especially since there is no science-based tag. It is sufficient to say "They have the tech to do this, but not that," and to change their mind to suit the needs of the world building.

• I think the 'washed up on shore' is the most plausible way to explain this scenario. They don't know how the receiver works - it just does. And since the Europeans made it, it will be tuned to the proper frequency. As others have noted though, learning a language based purely on sounds with no context, body language, props, etc., is likely impossible. – Tracy Cramer Aug 23 '18 at 20:21
• Aaron you recall,wrongly it was WW2 that the Germans set Zepplins along the British Coast to see if there was radar in operation. Apart from that the essence of the story is correct. – Sarriesfan Aug 24 '18 at 9:42
• Your idea about power needed to emit is brilliant. Americans could chat on their continent but they don't need to build inter-continental emitter. While Europeans need to build radio which could be recevied in Africa and India. At the beginning of radio era, beaming was not a goal so these transmissions could detect (accidentally!) at America. – ADS Aug 24 '18 at 10:44
• @Pureferret For directional, as per my previous comment, that is only true for certain areas of land. For a transmission from eastern Europe to western Europe, there will be a linear or triangular area that could extend across America in which the signal could be received. – Loduwijk Aug 24 '18 at 15:46
• Sorry, but the power arguments are based on a complete lack of understanding of both radio and industrial technology. You really only need a few watts to transmit across the Atlantic, and you need far more than that to manufacture radio components. The directionality arguments are similarly ignorant, of the fact that paths and gains are reciprocal. – Chris Stratton Aug 25 '18 at 1:52

How is it possible to capture long distance radio transmissions without the ability to transmit it back?

Is it feasible?

Definitely not. No one just invents just a radio receiver, if for no other reason than you can't test your receiver without having a transmitter.

Even if you develop a receiver that -- through wildly dumb luck -- just happens to be on the same frequency that Europeans are transmitting on, no inventor worth his salt is going to just stop there. His first thought will be, "how do I transmit back?"

EDIT: specifically, anyone smart enough to have knowledge of EMF and invent a receiver will be smart enough to (quickly) build a transmitter.

• Maybe the answer to "how do I transmit back" satisfies my initial condition: 10-20 years receiving without transmitting. – Chaotic Aug 23 '18 at 19:32
• Crystal detectors, the first radio receivers, were originally invented as a laboratory microwave optics detector. There was a gap of 8 years before they were utilized as communications receivers, and then at a much lower frequency. So "quickly" was nearly a decade. Similarly, there was 7 years between the transistor and the transistor radio. – user71659 Aug 23 '18 at 20:14
• @RonJohn Crystal rectifiers can easily be created by accident, all you need is the appropriate materials touching (pencil lead and razor blade). Second, the technology behind transmitters, to this day, is more difficult than receivers, due to the higher power levels necessary. Third, as you trace the development of radio, people initially tried too high in frequency (microwaves), then they got it to work at, what turns out to be too impractically low of a frequency (LW/MW), before accidentally discovering HF propagation. There's a lot of phenomenological unknowns that took decades of work. – user71659 Aug 23 '18 at 21:03
• Maybe it is possible to [accidentally invent a receiver]( newscientist.com/article/…). – Gary Walker Aug 23 '18 at 22:58
• @RonJohn You have the natural transmitters. Say lightning strikes. They are going to be transmitting, and have a very large bandwidth. You could notice that your device reacts to lightning strikes. – AndrejaKo Aug 24 '18 at 4:57

Many of us have heard stories about people picking up radio broadcasts like baseball games on their tooth fillings or dental braces. Perhaps some type of jewelry or adornment worn by the Americans works the same way. They don't quite yet understand how it works, but they can duplicate the item's construction, and even tweak it a bit to improve reception.

• If the OP doesn't want to have the Americans technologically advance themselves, this would be the only option. If the Americans do technologically advance themselves to where they were able to build the technology required to produce a vacuum tube or get a crystal just right (consistently), draw very fine wire, etc. then they'd probably also be out sailing around and be the ones doing the discovering instead of the europeans... – ivanivan Aug 24 '18 at 0:33

The only reason I can conceive of that a civilization would develop receiver radio technology, and no transmitter would be some form of radio telescope.

As others have pointed out, its highly unlikely someone would stop there, and not try to figure out how to generate the signals; but if for some reason someone made a Foxhole Radio, you could find a creative way to hand-wave it.

• This is a great and simple answer. I even like it better than mine. This perfectly allows OP to have great receiving tech but little to no transmit for the Americans. Similar to how other cultures had various technologies which they just didn't put to the same uses as the Europeans, like gunpowder. Similarly, here Americans were using the tech for something else and developed it without using it for another potential. They could get great receive tech, and later realize they are getting communications in and it could be a while before they transmit. – Loduwijk Aug 23 '18 at 19:27

What about an European ship lost at high seas, that somehow ends up on American coast with just a few survivors after months of starvation?

The ship would carry a radio receiver but the transmitter would have been broken or doesn't carry very far. The few survivors could help the native Americans get started in English language, which they could then better learn more about using the radio.

If it is important for the story, the few survivors could later die and fall into obscurity, while more radio receivers could be manufactured if they had some electronics knowledge to start with.

This topic

https://ham.stackexchange.com/questions/574/what-bands-and-modes-will-give-me-voice-at-3-000-miles

makes that seem pretty unlikely without some coordination between the 2 sides as to frequency to be used. Also the hardware needed is not something one could just throw together.

If you really want voice to anywhere in the world, you'll want a huge yagi antenna on a large tower, transmitting at the full legal power in a quiet RF area. Other than that, you will have some compromise

• Please quote some relevant sections from the link. Otherwise it might be closed as too much like "link only". – RonJohn Aug 23 '18 at 18:45
• Note that the question you refer to asks for something that will always work, which is a very tall order for anything shortwave. (That's why frequencies above 1.5 MHz -- yes, 1.5 MHz -- were originally considered to be useless, and therefore were assigned to radio amateurs. In 1936, all above 110 MHz. If you're interested, look up 200 Meters and Down by Clinton B. DeSoto.) It takes far less to have something that will work at least some of the time, especially if you only want to receive and the transmitter side is high powered. – a CVn Aug 23 '18 at 19:50
• @RonJohn, when the link is to another SE site, link rot isn't really a concern. – Wildcard Aug 25 '18 at 2:04

Yes. It could be possible. With some assumptions.

You don´t need advanced technology to build a receiver. Perhaps even some of you built at school a "Crystal Radio". It is an AM receiver. It uses only the power of the received radio signal to produce sound, needing no external power (no batteries, no plug). It is named for its most important component, a crystal detector, originally made from a piece of crystalline mineral such as galena. (This component is now called a diode).

The complete description is here: https://en.wikipedia.org/wiki/Crystal_radio

So, to make America able receive the signal, you need to find out a "reason" for them to have built something like this. Perhaps they were trying to build another type of machine for some other thing, and suddenly the "thing" started to talk in strange languages.

Although they don´t need to have developed radiocommunications, some technology will be neded (they need wire and a coil). And finally they need a way to listen (earphones). Piezoelectric earphones could be theoretically used if they have not developed their electromagnetic science enough.

What's to stop a container of them washing up on the America's shore? Downside is they're normally fairly short-range FM radios and are unlikely to receive local FM broadcasts from Europe or Africa.

Then lets say the transmitter culture has no particular power restrictions and has powerful transmitters capable of going a lot further.

OR how about a set of crank-powered shortwave radios getting washed up? Something a survivalist might have? https://www.ambientweather.com/kakahacrsopo.html#caption is capable of AM/FM/SW1/SW2 reception.

This could be seen as "deus ex machina" where the answer just comes from the sidestage and will distract from your plot.

Theres more to making a radio than the sum of its parts

Without prior communication, the Native Americans would need to have developed radio independently.

However, to make a radio you need a fundamental understanding of magnetism, electromagnetism, conductors, capacitors, sound, and perhaps even integrated circuits. To get these you need metallurgy, refinement and mining.

None of the above would be possible without the steady education and scientific rigour established in an Enlightenment, when scientific principles began trumping superstitious ones.

Even means of production would need to match - with experimentation coming from the constant bouncing of ideas in a scholarly manner in cities, and for this the cities need to be stable, large enough for a population to exist free from hunter-gatherer tasks. Which also means you need institutions established to promote cities, farming, engineering and sewerage, water distribution, waste disposal. To develop these, you need a sophisticated writing system to transmit knowledge, including also an understanding of mathematics.

These all go hand-in-hand with the development of science and education, leading after a long process, eventually to the creation of a radio.

If the above happened than it is equally likely the Native Americans would be as advanced as the Europeans - likely to that the would have travelled extensively too. They may even be teaching Europeans a thing or two.

• There is absolutely no need for integrated circuits to make a simple radio receiver, or even transmitter. Not even semiconductors in general are required (the term transistor radio was coined for a reason). Very basically, a tuned circuit (which can boil down to a capacitor and an inductor, chosen appropriately) with a linear mixer stage will form a workable, though very low audio output power, AM receiver. Add a power amplifier stage after the mixer and it's actually useful. Add a beefier amplifier stage and rearrange the components slightly, and you pretty much have a basic AM transmitter. – a CVn Aug 23 '18 at 19:41
• Such an AM transmitter wouldn't pass the spectrum purity requirements of today, but it would allow you to transmit. FM is a bit more involved, but FM (on any frequency) is terrible for intercontinental transmissions anyway for reasons unrelated. – a CVn Aug 23 '18 at 19:41

## The Two Go Hand In Hand, Scientifically

Generally speaking, the scientific background knowledge required to build a receiver is the same as for a transmitter. It is not really believable that someone could do one and not the other. At least, not for long.

High-power, noise-free transmission, however, is very difficult to achieve. In practical terms, your choice is between disparity in power generation or ignorance of radio/electromagnetism.

Radio transmission requires power, and the power level increases dramatically with the distance you intend to transmit.

It is entirely possible that your European broadcasters are pushing hundreds of watts, or even kilowatts. In the right bands, those signals could be received around the world.

Your American natives could have the exact same radio tech---and even communicate with each other via radio---but still lack the power required to respond to the Europeans.

A radio would need far more power to transmit overseas than to receive. A modern radio needs only ~5W to receive and power its speaker (and some work with less), but it could output 100W+ broadcasts and still not be heard overseas.

## Technological disparity

The Americans could have a primitive device they built, or they could have a European device which they do not fully understand.

It is possible that the natives' European-built radio was acquired via theft, trade, or salvage. Perhaps it is damaged and cannot transmit.

They could even have a device capable of communicating with Europe and just not know it. Maybe they're held back by nothing more than the flip of a switch or the press of a button.

• Almost, but you're making the same transmit power mistake as all the the many more uninformed answers. Transatlantic transmissions are really a function of ionospheric propagation, not transmit power. Propagation is mostly a function of frequency vs. sun activity and time of day. Differences in transmit power only matter when there is a marginal path you are trying to make the most of. When there is a decent path, you really don't need much power - 100 watts is sort of a convenience norm desktop transceivers are built to, but you often need far less. – Chris Stratton Aug 25 '18 at 2:00

Radio receivers can be very, very simple. A badly done dental filling can end up making one out of one of your teeth and suddenly there are voices that only you can hear.

A crude crystal receiver could easily be accidentally created as a piece of artwork if both an amplifying crystal and a piezoelectric crystal were part of a wire sculpture and things got wrapped in just the right way. (Teeth are both, hence why a bad filling can make a radio.) From there add some tinkering to make it work better and they could conceivably end up with decent receivers.

The North American groups didn't really attain the level of technology where it would be likely to do this, but several of the South American tribes did, and even had what appear to be primitive acid batteries in some of their ruined temples, though what they used them for we don't actually know for sure. Had there been intelligible transmissions at the time they might well have stumbled upon a receiver at some point.

The amount of power necessary to transmit that far would likely be prohibitively expensive for the Europeans of the time though and learning a language with no reference context is rather impossible, so that will be your big problem... but I have run across theories that South America may have been visited by the ancient Greeks and/or Romans at some point, so if your transmissions were in Latin there's a tiny possibility that someone on the receiving end might understand them. But you'll still need a reason for the Europeans to be running megawatt transmitters when kilowatt ones would serve their needs perfectly well... Maybe they're communicating with colonies in Africa?

Honestly, I don't think the above scenario is feasible.

The Native Americans could not know about these transmissions from Europe without having the means to receive them. This means that they would have, for unrelated reasons, developed radio technology independent of the Europeans.

Moving on, why would they develop a device that could receive but not send transmissions? I simply can not think of a practical purpose for this.

And so if they had developed radio technology they would almost certainly have the means to send AND receive the transmissions and they would be able to reply to the Europeans.

Maybe a scenario where the Native Americans for some reason (religious or otherwise) decided not to reply to the radio transmissions that they had received would work better.

I recall an old Radio Shack kit that was a very simple crystal AM receiver. I had it as a kid, though I don't recall if I ever got it to work very well, but it certainly was simple enough and needed no outside power, or not much.

In any case, in aviation, we use receive-only radios for a lot, including navigation and weather. Even some communication is done with split radios using one object, like a navigation station, to receive, and a completely separate channel to transmit.

The biggest problem I see with the OP's presentation is creating a receiver that operates on the correct frequencies being transmitted, and suitably notching the correct frequency or otherwise suppressing spurious noise and transmissions, to make the intended transmission intelligible.

Would they really want to transmit back ?

It is straightforward to find transmitters using radio direction finding methods.

If for example SETI found signs of extraterrestrial life, would you really want to send a signal to them to meet us ? (to invite them to take our resources etc. ?).

Another idea: in the movie 'Galaxy Quest', extraterrestrials see our daily TV transmissions as 'historical documents' since their civilisation is much more advanced. Probably it was quite amusing for them but as far as I remember they did not see a need for communication or visit for a long time.