I'm just going to go with the scenario of 'the specific part of the EM spectrum that we use for comms is no longer accessible to us'.

So, mobile data and GPS are out. A heck of a lot of people suddenly get very lost, and the immediate aftermath would include a lot of car crashes- mostly from people trying to play with their phone while driving, or just generally being distracted. Long term, people would get used to having to find themselves on a map. I doubt street directories would make a comeback, as it's relatively straightforward to download a map to a phone by plugging it into to a computer, or USB to Ethernet. Oh, in that regard- The shortage of USB to Ethernet adaptors would probably hit before the toilet paper shortage.

There's a large portion of the world's population who like to stay inside and listen to the radio or watch TV, the internet still being an unwieldy thing that the yung'uns use. These people will start getting their entertainment and news by walking outside and congregating - At least until they get a computer or phone setup wired. Hopefully, many will continue to go for walks around town to see their friends and eat a meal. A lot of households are going to have a whole lot of Ethernet cables run all over the floor for quite some time. People will start buying switches and routers to get more outlets next to the couch, for example.

Massive queues will form around the few existing payphones, until businesses and homes at central locations will start offering up ethernet ports. Because this started soon after the Blackout, rooted in generosity and helpfulness, this will just become a free service.

Taxi drivers will start congregating at these spots, plugging in and updating their location, moving to other locations where there is few drivers- and hoping that others aren't getting the same idea, unable to know that until they arrive. The old guard of taxi drivers, who worked pre-Uber and have an encyclopedic knowledge of the local streets are in high demand, and people seek them out.

A lot of scientists are out of a job. People who worked with radio astronomy are suddenly having to peer through optical telescopes again, and keep talking about the good old days. Whole divisions of people at space agencies, responsible for things like monitoring and control of satellites, space probes, and rovers are suddenly retasked to creating ways to create autonomous return probes to find out what the fuck just happened. Some start trying to work out ways to replace radio by using giant scaled up versions of television remote controls, putting giant infrared lights on mobile phone towers, with smaller repeaters on top of houses and cars. (For funsies, I'm assuming point to point microwave comms are out- which has the implication that microwave ovens don't work any more, with the associated knock on effects of house fires from people melting microwave dinners in ancient, unmaintained conventional ovens).

People who worked with wireless stuff- from FM radio DJs to antenna design engineers are all out of work. Perhaps they start selling coffee to people stopping by those public ethernet locations? Unfortunately, there's a noticeable economic downturn from so many vacant jobs, people being out of work suddenly, and commerce becoming so much more difficult. Cash becomes much more useful, and those handy dandy wireless payment terminals don't work so good anymore, and while waiting for wired replacement terminals to arrive, people get used to cash again. There's a knock on effect of people keeping cash to themselves, despite the government being almost completely unchanged. This downturn, along with jobs that don't exist any more, puts a lot of people out of work. However, they are likely to start filling the jobs left vacant by the thousands of people who perished in the utter chaos that was every aircraft on the planet trying to land at the same time in utter confusion.

A couple might make it safely down, but it only takes one accident- say a little Cessna coming in low, not seeing the 747 coming in faster from above, to turn the runway into a total mess of burning jet fuel, wreckage, and stunned people slowly bleeding out, surrounded by smashed bodies and assorted socks. Aircraft block major highways attempting to use them as runways, often causing huge multi-car pileups by giving already already distracted drivers a totally insane thing to have to deal with. Many pilots take the opportunity to 'do a Sully'. Hundreds die as waterways around major airports become congested with crashed aircraft, with many potential rescue personnel sleeping through the whole thing, because who the heck has their landline phone number, even if they have an actual phone plugged into the wall?

In short, I'd watch that movie. Maybe a series in three parts, immediate, a few months later, and then years after. Great question OP, thanks!

Oh, also- people who made special effort to get a phone that has a headphone jack will be smug as fuck for a very long time.

Their transmitting power they use is so powerful, its jamming signals are 1000 times stronger than the strongest radios we have

Strongest (declassified) radio transmitter is (likely) the Eglin AFB Site C-6. https://en.wikipedia.org/wiki/Eglin_AFB_Site_C-6. Peak radiated power is 32 megawatts, it operates at a bandwidth of 10MHz.

32MW is about 105dBm. Times 1000 will add 30 dB, so the alien transmitter will be at least 135dBm, which corresponds to 32GW.

Given the Friis Transmission Equation, 135dBm with a transmit antenna gain of 1dBi, at a distance of 12,756km (diameter of earth), a receive antenna with a gain of 1dBi, will receive a signal of: 22.44dBm at 1MHz, 2.44dBm at 10MHz, -17.56dBm at 100MHz, -37.56dBm at 1GHz, -57.56dBm at 10GHz, adding an additional 20dB of loss per decade. This is completely ignoring all effects like atmosphere and ionosphere, signal traveling through or around the earth, reflections, any funky propagation, or constructive/deconstructive interference patterns that may occur. Also ignoring antenna gain.

A rule of thumb is that the signal-to-noise ratio (SNR) should be at least 5x (or about 7dB) in general and some digital modes will tolerate it. 20dB is usually the minimum recommended in general, with 25dB or more being recommended for voice.

AM radio at about 1.5MHz will still work- but only for about 1km from the tower. At this point the AM signal from a 100kW transmitter would be about 46.03dBm for a specially designed antenna and receiver, but the noise level would be about 22.44dBm. Realistically, AM will not work and may even blow out a receiver front-end. Television at about 88MHz will be usable for only about 1km using a specially designed receiver, normal TV likely won't work at all.

GPS is around 1.5GHz and the typical levels received are about -130dBm. Our noise is about 90dB or 1,000,000,000 times stronger than the received signal. No chance of GPS working at all. Wifi is around 2.4GHz or 5GHz and a "perfect" signal is about -30dBm. The received noise at 2.4GHz would be about -45.17dBm, and at 5.6GHz this would be -52.53dBm, so feasible that wifi could still work if you are close to your router/antennas.

Cell Phones have an extremely wide range of frequencies. On the lower frequency end, they likely won't work. For something like K band at 10GHz, the phone itself would be transmitting about 33dBm. At a distance of 2 km, the cell tower will be seeing about -83dBm from your phone, while the the noise received will be far higher at about -57dBm.

Lastly, Submarine communication is typically done at ELF (3-30kHz). They typically need about a whole power station dedicated to powering it, and the effective transmitted power will be something like 5 watts or less. A submarine at 100km might pick up a signal of -2.99dB on the surface (realistically, far far less when submerged due to sea-water attenuation). The noise level on the surface from noise would be 52.9dBm.

This is all assuming that somehow, the aliens have a perfectly efficient wide-band transmit antenna. And have landed on earth with their super transmitter. And all of these numbers assume that max transmit power takes up the same bandwidth as the signal of interest.

In practice, the aliens would want to be far away from us. No closer than the moon, let's say. And they probably will want an array surrounding the earth to maximize line-of-sight. To maintain the previous numbers, they would need an additional 25dB of transmit power. And probably an additional antenna on a ship, opposite to earth from where the moon is. So that's an additional 3dB of power required (x2 for 2 antennas).

They could probably knock off about 20dB if they used high-gain antennas. But let's say they use that power to further overwhelm earth's ability to use radios, even for edge-cases.

They would require 163dBm- about 20TW of power. To jam a single frequency listed above.

Let's say to jam the TV station, they were broadcasting over a bandwidth of 6MHz. That gives a power-spectral-density of 3.4MW/Hz. To cover the entire spectrum at the same time, say 10kHz to 300GHz, they would need just over 1 exawatts. 10^18 watts. That's a lot of power! They could use a partial dyson sphere with the sun, but we could say the aliens are nice enough to still allow the sun to illuminate the earth and other planets to keep everything else the same.

My phones/tablets would be dead in the water, but I avoid wifi for almost everything not actively mobile. So all my iron - even the laptops - are hardlined.

Unless they’re looking to employ Carrington-event-class interference, my networks are fine.

This is an underpinning of the plot of Final Fantasy VIII, where a sorceress with incredible power is entombed and sent to space, and her screaming drowns out all the radio frequencies on the planet.

Pulls out my big box of old CAT5 cables... Who's the packrat now?!

Wired communications would take over immediately and it would be a massive pain in the ass, but we'd ultimately adapt.

If the EM jamming is enough to also degrade the signal in copper lines, which at 1000x the strongest signal, might happen, then basically all modern society would collapse within 48 hours

we use wired communications until the issue is solved.

What does it look like in the long term?

If they don't stop, we'll start using their jamming as a source of power for small mobile devices. It's free energy at that point.

In the three body problem books one of the main plot points is a very similar scenario (although not identical). No spoilers but it might be worth a read / watch.

Jamming isn’t so trivial because it’s not really the volume but the signal to noise ratio that really matters no matter how much energy the aliens use. Therefore, I propose that this question doesn’t make technical sense.

Take for example GPS. The signal strength is way below the noise and you can’t really hear it at all because it’s so weak. The background noise is overwhelmingly loud already. You have to process the signal out of the noise using special techniques to collect the energy you care about using statistical correlation. While can still jam the signal in general, jamming requires that you understand how the signal is being used to impact that signal to noise ratio and stop the information flow. Simply screaming into all frequencies might not have all that much impact unless you understand what a signal means for each use case. Many wireless applications are even point to point links that are great at rejecting inputs outside of the intended direction and even the wrong polarization. There are physical limitations that preclude a general all signal jammer.

That said, let’s say the aliens understand all of our wireless communication protocols. I think people would adapt after a short period of disruption because it wasn’t all that long ago that we were using wires for business and critical functions. Heck, some industry still use fax machines and famously a lot of old government tech still has software stored on floppy disc. I think we’ll be OK. Might even be better for our mental health once the phones stop working.

I am sure someone will use it as a pretence for invasion. I loosely remember reading somewhere that jamming can be classified as an act of war but I don't recall where I heard it.

My whole family is going to start complaining that the WiFi is busted and I need to fix it.

(Please don't say "kill the aliens" they have tech so advanced, its impossible to do it)

Usa would send all their nukes in an attempt to kill the aliens anyway, because otherwise some top militarists would feel their whole life meaningless.

So, EVERY radio on the planet is suddenly overwhelmed by broad-spectrum jamming from orbital sources? Every cell phone, wifi, broadcast TV, satellite, AM/FM?

A bunch of people die,.due to distracted-driving car accidents with no way to call for help. News and government adapt modestly quickly, since the Internet itself runs mostly on already-shielded wires. There is a run on ethernet cables and phone modems for a bit, though, since not everyone has one. Navigation and timekeeping get harder, since no GPS or radio time sync, but humans adapt to those fairly quickly.

Long-term consequences depend on how long the aliens keep it up. It's definitely a holy crap there are aliens! moment, though, since a bunch of sudden radio transmitters would be detected in the sky and identified as alien tech way before the toilet paper shortage even starts.