Even small countries have a few ~30 m diameter parabolic antennas but nobody reported signals coming from the landers on Mars. How is it possible? [duplicate]

The parabolic antennas with diameters of ~30 meters are all over the world. Even small countries have them. However, nobody, except DSN or other entities controlled by the US government, has ever heard an American rover or lander transmitting from Mars.

One might argue that not all these antenna have 7-8 GHz receivers. They can be fitted in a matter of hours. This involves just a minor change at a small cost. Besides this, there are numerous smaller antennas with diameters of 10-15 m that are enough for detecting simple carriers of martian origin.

Random example:

Source and technical characteristics:

Also most countries in the World are well capable of hearing the noisy landers on Mars, no one reported man made radio signals originating from them. How is it possible?

• please take your conspiracy theories elsewhere. Not only are they based on poor data and assumptions, you could answer most of them yourself with a bit of research. – GdD Mar 2 at 8:21
• So now that non-US entities have both photographed the lander and picked up its signal, you're going to gracefully accept that you are wrong and stop posting this junk, right? – Organic Marble Mar 2 at 12:58
• I am trying hard to understand your stance with all of your questions that imply that Perseverance does not exist. You ask questions that have a conspiratorial bent but then accept answers that disprove the conspiracy theory. It appears you might not be a conspiracy theorist but instead are trying to debunk those conspiracy theories. That is not what we do at this site, and that is why you are questions that are heavily downvoted, closed, and sometimes deleted. It is axiomatic at this site that the Earth is not flat, that humans did plant footprints on the Moon, and that spaceflight is real. – David Hammen Mar 2 at 13:01
• Arguing with conspiracy theorists, of whatever bent, is an unwinnable game of Whac-A-Mole. If one does smash down one nonsense conjecture, another pops up (or two more pop up). We just don't play Whac-A-Mole here. – David Hammen Mar 2 at 13:14
• Stripped of their conspiratorial tone, I find the questions quite reasonable and curious. I've learned a lot answering them. Unfortunately the OP's denial and goal post shifting and agenda pushing has tainted the whole endeavor. – Schwern Mar 2 at 17:35

tl;dr: Anyone with the capability is either working with NASA or has better things to do with their dish.

Nobody except DSN, has ever heard an American rover or lander transmitting from Mars.

This is not true. Both Green Bank Observatory and Max Planck Institute for Radio Astronomy received signals from the Perseverance EDL (entry, descent, landing) using their 100m antennas. They did the same for Insight. You can watch Green Bank's live stream of the event, they discuss the observation at 2:35:00 (not a lot of technical content).

But the premise of the question is that any old 32m antenna should be listening in, right?

The technical issues with hearing a Mars rover with a 32m antenna have already been addressed, it's pretty hard. And I'll let someone else address how difficult and costly it would be to fit an existing dish to receive the X-Band signals Perseverance transmits.

Receiving signals from Mars isn't like turning on the radio in your car. Dish antennas are directional. In order to receive signals from Mars a dish has to be pointed at Mars. So that limits it to steerable dishes.

The apparent size of an object in the sky is its angular diameter. For a distant object like Mars its diameter divided by its distance equals its angular diameter in radians.

Mars is currently about 200,000,000 km away and about 7000 km in diameter. At that size and distance it covers $$\frac{7,000}{200,000,000}$$ or 0.000035 radians or 0.002 degrees of the sky. This is quite small. To compare, the Moon is 400,000 km away and 3500 km in diameter covering $$\frac{3,500}{400,000}$$ or 0.00875 radians or 0.5 degrees of the sky. The Moon appears 250 times larger than Mars.

Which is to say, a 32m dish won't just happen to be pointed at Mars. They would, at minimum, have to be deliberately pointed at Mars. They aren't.

Why aren't they pointed at Mars?

Because they're extremely valuable and expensive pieces of equipment in high demand by radio astronomers and others. It's not their job. The DSN and their auxiliaries like Green Bank do it just fine.

The exception is Goonhilly, a commercial operation who are attempting to receive from Perseverance to demonstrate the deep space capabilities of their new GHY-6 32m antenna.

Goonhilly will be leading the world’s first commercial deep space network service to provide additional capacity that will extend existing NASA and ESA deep space networks.

• Did the Max Plank institute receive signals from Perseverance itself while descending or from an orbiter that retransmited the data? What communication system (the characteristics) did Perseverance use during its descent? Did the Max Plank institute continue, for a while, receiving signals after Perseverance landed? – azot Mar 2 at 7:40
• @azot Thank you for accepting the answer. I don't have details for Max Plank. I think that's a new question. – Schwern Mar 2 at 7:45
• @azot Doing some more research, Perseverance also relays through the ESA ExoMars Trace Gas Orbiter and the ESA's own Estrack network. No US. No DSN. Can we be done now? – Schwern Mar 2 at 8:20
• @azot Nothing involving liquid helium is easy, nor at the sensitivities required to listen to a ~50W transmission from Mars on the surface of the Earth. And, again, what would their motivation be to spend all that time and money? Perhaps you have your next question: what would it take to upgrade a 32m dish to receive X-Band from the surface of Mars, and what else can that capability be used for? You can also ask the folks at Goonhilly who are doing just that, their motivation is profit, but be respectful. – Schwern Mar 2 at 20:39
• – uhoh Mar 3 at 0:24