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Author Topic: My SETI Project  (Read 4735 times)
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This thread will contain updates on a new project. The goal is to detect radio wave signals from an extraterrestrial civilization.

Please use the General discussion for posts

Mystery Man answered an interesting question about me detecting radio wave signals from an extraterrestrial intelligent civilization.


He said about 400 light years away if he helped me design the receiving equipment. After searching around I just learned that even SETI would only be able to detect a strong tv transmitter about 1 ly away. That’s just great because that doesn’t even put us outside our solar system. Our Oort cloud is about 1 ly in radius. Here’s an interesting page on this.


Scroll down to read the last answer by Rob Jeffries. It turns out that SETI only hopes to detect extremely intense radio signal bursts that would be extremely uncommon. Wikipedia lists some north american broadcasting stations. I’d say 200 to 500 KW is a strong station. I’m thinking that Rob’s answer is very conservative. It would be interesting to see how much voltage such a signal would produce on a high gain receiving antenna. Although it depends on the frequency. A good portion of the radio wave spectrum reflects off the ionosphere, significantly weakening signals that escape the planet.

In order for me to detect the signals coming from that source 400 ly away I would most likely need help from MM in designing the receiving equipment. Although maybe I already have something capable of it because a year or so ago I came up with a method that I’m confident could detect the signal, but the problem is that the method requires a lot of sampling. So I would not be able to hear their voices over the radio waves. My method relies upon the ET signal fading in and out as their planet rotates. As the planet rotates, the transmitter will go behind the planet, thus eliminating the signal. So the signal would modulate. I should be able to tell if it's a signal made by intelligent beings by the spectrum of the signal and how coherent it is.
« Last Edit: 2017-08-23, 23:06:46 by Theoretical Research »
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This has to be one of the most amazing websites I've ever seen. Use your mouse to rotate around. The mouse scroll wheel zooms in and out.


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Here’s some results. I placed a dipole antenna 1,000,000 meters away from a high gain 56 element yagi antenna. I could build that one. The dipole is transmitting 200 KW. A 70 ohm load on the 56 element input element was 20 uA, which comes to 20 uA * 70 ohms = 1.4 mV. Receiving voltage in an antenna is relative to distance. At a distance of 400 ly the voltage would be 3.7e-16 volts. So 56 elements is insufficient.

If we drop the temperature of the load to 190 K, dry ice, with 450 Hz BW (plenty BW to hear voices, at least on Earth) the noise voltage is

sqrt(4 * k * 190 K * 70 ohm * 450 Hz) = 18 nV

One can expect about 1 db gain per extra element in yagi antennas, which increases the voltage by a factor of 1.122. If we add 154 more elements to the 56 element yagi antenna :) the voltage comes to

3.7e-16 V * 1.122^154 = 18 nV

That’s 154 el + 56 el = 210 elements. Sounds crazy.

According to parabolic dish antenna calculators the dish would need to be 4100000 meters in diameter, which is about 1/3rd the diameter of earth. So dish antennas won't work for me.

If we drop the load temperature to 1 K and use a special low temp amp and drop BW down to 100 Hz, then we only need 180 elements.

Anyway, 210 elements is a lot! I’ve seen photos a HAM radio guy with a 100 element antenna. You would have be good with antenna analysis software, make very accurate measurements, and know what you’re doing, and even then I’m not sure if you could get close to the required gain. Also it would have to be in a relatively quiet location on Earth due to the 18 nV input. That sounds like low input voltage, but it’s not. Trust me! I’ve spent lot of time working with metal detector designs that were considerably lower than that.

The bad thing about yagi antennas is it works at one frequency. Unacceptable to SETI, but maybe MM could tell me the magic frequency, if he knows it. ;) Dish antennas are wide BW, but it comes at a cost of being way to large. One third the diameter of Earth!

Does all my math work out?
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I just read in an amateur radio forum that 100 element yagis for SHF are not unusual, they're already on the market. So on google I found people building 200 element yagis, 300, 400. I stopped googling at 500 elements. Looks like it will work. I just need to know the frequency. I'm sure the 210 element yagi would have plenty of BW to hear voice.
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There's an article on a fully electronically reconfigurable 400 element antenna. Sounds like a nightmare to build, but once completed it would allow you to scan a broad frequency range at incredible gain.

According to my calculations a 210 element yagi at 1.5 GHz would be 6.9 meters long.
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For someone who doesn’t know where to look in the sky and what frequency, this might be the best plan. Use my modulation detection method to find a signal, and then use a 200+ element yagi antenna method to hear the signal in real time. That's when you'll be listening for ETs voice.

A planet rotates. So the signal is going to modulate at the rate the planet rotates. You would use a long term sampling method. I doubt you could use a FFT function because you wouldn't have enough memory or cpu power. There are simple relatively low cpu intensive techniques you can do in software to detect the modulation. It might take up to a year of sampling to spot the signals. Once the signal is spotted you build the 200+ element antenna and point it at that direction to hear ET.
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Good news and bad news.

Bad news. I wasted the entire day yesterday working with antenna optimizers. First 4nec2, then Nikiml’s optimizer. Both optimizers have serious issues, which ended up being a waste of a day. I got a 28 element yagi on 4nec to over 60 db. Obviously in error. According to 4nec2, there are no errors or warnings. 4nec2 will tell you if wires are too close, etc. etc. There are some wires very close to each other, but they’re within the legal distance. Maybe at higher gains the nec limitations increase.

Good news. An idea for a digital antenna. Imagine a radio wave in front of you. Lots of wavelengths, traveling at the speed of light. A very long yagi antenna is in front of you. Connected to each element is a simple circuit that takes a quick sample once per cycle. At t=0 the first element takes a sample and sends it to the main circuit. Perhaps via optic cable or whatever. At t=1 the 2nd element takes a sample. At t=2 the 3rd element takes a sample. And so on. The spacing between all of the elements is the same. The spacing is less than one wavelength. So if you have 10 elements, then the spacing is w - w/10, where w is wavelength. I think the math is right... So if the signal is coming directly in front of the antenna, then the net signal to the main circuit coming from all of the small circuits in each element will be DC. The more elements, the better the digital antenna will be. The only limitation is in how much you can afford to make. It could literally be a million elements. Two million would be twice as effective, just as 200 elements would be twice as effective as 100.

The main problem is noise. The second problem is the side lobes. The digital antenna solves both problems, but another problem arises since the ET signal is so weak-- Bandwidth. The more elements our digital antenna has, the lower the beamwidth and bandwidth. In order to overcome noise we have to decrease the bandwidth so low that we won’t be able to hear voices. Not unless ET speaks extremely slow. A quick rough calculations comes to about 500 uHz BW.

Any ideas? The digital antenna was an amazing breakthrough, but it seems we’ll need some magic to get this to work, unless MM comes to the rescue. :) He did say that I would need his help.
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Oh a possible solution to the problem mentioned in the post just made above. Regarding each of the small circuits found in each element, instead of taking a short sample, we can instead shift the phase of the signal by an appropriate amount and send that signal to the main circuit. What will happen is that the main circuit receives signals from the elements are all in phase because each element circuit shifts the phase by a specified amount. The phase shift amount varies from element to element. If we have 400 elements, then the SNR drops by sqrt(400). So great. If we have a 10 billion element digital antenna we can hear ET talking haha. Idk, I haven’t done the math. Maybe it won’t take that many elements.

As a side note, the overall temperature of space is 2.7K, which we’ll be picking up in the antenna. If we place a good reflector underneath the antenna we can shield most of the terrestrial ground noise. Not sure how much atmospheric noise there is. The circuit noise can always be lowered with temperature.

The above is for the 2nd stage. The first stage, which seems solid and easy enough, is where we do long term sampling, which gives us ET’s location and broadcasting frequency.

Any ideas please post in the general discussion
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Success! Assuming my code is bug free. Attached are 3 screenshots of my SETI project stage 2 system simulation. It’s what I would call a digital antenna. The screenshots are for 10 elements, 100 elements, 1000 elements. The vertical axis is voltage that the entire digital antenna system receives. The horizontal axis is in degrees. The far left of the image is 0 degrees. The far right is 90 degrees. So 0 degrees is head on. That’s the direction you want to point toward ET’s home world. Light that enters to the side of the antenna would be 90 degrees. As you can see in the screenshots, the spikes increase in density as we approach 90 degrees. Although the width of the spike decreases. So the average voltage from spike to spike is the same. The number of spikes is relative to the reciprocal of total elements. So if you double the number of elements, the overall unwanted signals drops in half. The signal we want is at 0 degrees. All of the other spikes are unwanted.

Hopefully tomorrow I’ll do some math to see the minimum number of elements the digital antenna will require to hear ET at 400 light years away broadcasting 200 KW.
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A lot of details need to be added to the SETI simulation tomorrow, and then I'll write the stage one simulation, which is the long term sampling method to find ET in the sky and the frequency. The present sim uses an unchanging single frequency, but a real ET signal will be amplitude or frequency modulated, which could change the sim results a bit.

There are several parameters that change the digital antenna characteristics. For example a simple change eliminates the spikes, but it widens the initial (the one at 0 degrees) beamwidth, which is why I did not use that antenna design. If the antenna is inside a deep canyon or inside a wire mesh tube to block side signals, then we may not need to be concerned about the side spikes since there will be no appreciable signals at those angles.

So the side lobes can be sufficiently shielded, the digital antenna doesn’t need that many elements. The 10, 100, and 1000 element versions all had a beamwidth near 0.2 degrees with that design, and that can be decreased. The problem is that decreasing the beamwidth results in more side lobe spikes. The optimum setting will depend where the antenna is. I think if this has a chance to work, then it will need to be far away in a quiet location, perhaps the middle of the pacific ocean, or NRQZ (National Radio Quiet Zone), a large area in the U.S. designated as a radio quiet zone. It’s illegal to broadcast signals in the NRQZ to facilitate scientific research.

One advantage to adding more elements is that SNR decreases since all of the signals coming from each antenna element are summed. In the center of each element will probably have a very tiny high frequency low noise amplifier, perhaps a simple transistor amp. That will feed either a coaxial cable or a high speed photodiode to a fiber optic cable.

That’s the plan. It'll be a miracle if this relatively tiny antenna can detect a 200 KW signal 400 light years away with enough bandwidth to hear ET. Insane. It’s interesting that this digital antenna design relies upon each element shifting the phase angle by a certain amount. The phase shifting will be done by adjusting the length of the cable. So, really it’s ... phase shifting. I wonder if that's what MM was referring to when in September 2014 he recommended using phase shifting to contact ETs. I doubt it.
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I added some info on each screenshot and changed the phase factor to 0.9.  This phase factor makes the digital antenna like a conventional antenna.  bw is beamwidth. At 10 elements it's 18.1 degrees, 100 el is 5.9 and 1000 el is 1.8 degrees. Yesterday screenshots had a higher phase factor, which lowered the bw to 0.17 degrees, but also added the spikes. Please excuse my programs excessive precision display; e.g. 1.797300 degrees. I didn't bother rounding the numbers. The green lines show angle starting at 0 degrees and ending at 90 degrees in increments of 15 degrees. So 0 degrees is facing the antenna head on, and 90 degrees would be when the radio waves enter the antenna from the side.
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Here’s the results of an ideal setup. There’s still more details to add that will probably decrease the SNR. Maybe in a day or so I’ll recheck the math for errors.

According to the simulation results, and given the present digital antenna design, it would take about 15,000 elements to hear ET’s voice 400 light years away broadcasting at 200 KW. That's 2,350,000,000,000,000 miles! Although it would be bad quality audio with an SNR of about 0.5. I’ll have to add some noise on an audio file one of these day to get an SNR of 0.5. I'm betting I’ll be able to understand a lot of the words.

This snapshot shows 180 degree antenna sweep. The green vertical lines are in increments of 15 degrees. Phase factor number was changed to a different format called Phase shift. I was going to put it in units of degrees, but from a design standpoint it was easier to work in wavelengths. The beamwidth is 0.468 degrees.
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