EME Moon Bounce: There has to be a signal in here somewhere!

I am not sure how close this is to what you want but the article by Bill Carle (VE2IQ).

If there is anything closer it might be on the ARRL web-site.

From 1946:

The moon is actually a pretty big target.

It is impressive how good an RF link can be. I can unlock my Audi from almost a block away, with the little key fob transmitter, and no visible receive antenna.

Radar bounce has been done on other planets, Venus and Mars I think.

One should be able to put up an antenna and detect the moonbounce of, say, a TV station signal. It would take some signal averaging.

Bit of a daft question, I know, but what sort of range would say a 10W transmitter in free space orbiting the moon have at the optimum frequency for maximum range and a practically feasible beam antenna (or an isotropic radiator if there are no figures available for anything fancier)?

What bitrate?

I forget what power level, but the Pioneer and Voyager probes aren't far from that range (directional antenna, probably a few watts), and obviously, much more distant than the Moon. They're still being picked up (what ones are still transmitting, anyway), albeit by rather elaborate receivers. The signals are deep in the noise floor, recovered partly due to their low bandwidth and high stability, and through long integration times and interferometry across multiple receivers.

I recall hearing that aliens won't be knowing about us after all, because after a good 50 light years or so, there really just isn't enough left to detect. Even if you know what you're looking for (correlating against, say, a known perfect recording of a given vintage transmission), the SNR from that integration time just doesn't give enough confidence interval to say so. And that's already having the transmission, which defeats the purpose of looking for it anymore. :)

Tim

The "unlocking" distance is heavily influenced by the RF pollution. That is, the receiver in the car doesn't have much filtering. Your distance can be reduced greatly if you are in the present of one of those Navy 380MHz land mobile radio systems.

What is -170 dB! ?

-170 dBm ?

-170 dBW ?

-170 dB under Tx power about -170 dBW = -140 dBm ?

The noise density for 300 K noise temperature is -174 dBm/Hz.

Since the data to be transferred is about 100 bits to be transferred in 18 minutes or about 1000 seconds, so th effective data rate is about 0.1 bits/s and hence the required bandwidth in the order of 0.1 Hz and the thermal noise in that bandwidth -184 dBm.

That would be the case with a simple white noise channel. However, the EME path is quite nasty, first of all, there is the libration fading due to the elliptic orbit of the Moon and hence the Moon does not _exactly_ turn the same side to earth (there is about +/-5 degree variation).

The other is the relative motion of the Moon and rotation of the Earth, causing Doppler shift (easily predictable) and the issues with transmitter and receiver frequency stability and accuracy.

One way to get around these is to use some form of direct sequence spread spectrum signals, but again, the Rx bandwidth after despreading is still well below 1 Hz to reach such sensitivity levels.

Of course it helps if the antenna beamwidth is so narrow that the dark part of the lunar disk can be used during the first quarter, since after a two week lunar night, those areas are about 150 K, reducing the thermal noise.

Ham radio operators have been known to do it with ~kW class transmitters and beep and nothing very special on the receiver.

That isn't so good. A bad guy with one of the Russian digital lock code grabbers can snatch your cryptokey if they are inside the key fob range. Mine is good for about 50m I think the car antenna is hidden in the rear view mirror since not all models have a bluetooth fin on top.

And imaging grade delay-Doppler on loads of asteroids since then. See:

Basically they transmit exotic almost orthogonal waveforms so that the ground based correlator can obtain exquisite temporal resolution and signal to noise of the echo profile from the target.

I knew a radio ham who used to do it for a demo Morse code. Crude ~2kW xmit fairly directional aerial and a moderately sensitive reciever.

Optimum frequency is answerable assuming no new super low noise technologies have emerged since 1985 (probably they have). 2.5-4GHz with a 15K HEMT (fancy MESFET) best or a 4K maser front end.

Noise floor limited by galactic noise at any lower frequency, microwave background in band and amplifier system noise above about 5GHz.

You'd probably want to transmit inside the radio astronomy protected band if you wanted to be seen from the maximum distance. There is a lot of background noise from WiFi etc at some otherwise good frequencies.

I'll give you the definition of the Jansky and let you try plugging in a few numbers:

Back in the 1980s it was possible to say that the entirety of all the signal that had ever been observed from pulsars was less than the energy released by dropping a match head 1mm. These days it is probably an order of magnitude more in total as many more ultra faint pulsars have since been discovered using realtime FFT hardware.

What difference should the temperature make?

Actually, what *is* the albedo at radio rather than optical frequencies?

Tim

Depends what waveband you are measuring in and whether the moon is like a black body at the relevant frequency. A typical big dish ground based antenna telescope like the VLA has a system noise temperature of ~20K if it is a Cassegrain design with the sensitive bits facing cold sky.

Penzias and Wilson worked at 4.08GHz and with their big horn got:

Zenith temperature observed = 6.7K @ 4.08GHz

Of which the accounting was as follows:

Atmosphere 2.3 +/- 0.3K Ohmic losses 0.8 +/- 0.4K Sidelobes 0.1K TOTAL 3.2K

The difference 6.7 - 3.2 = 3.5K got them a Nobel Prize (after they had cleaned every last trace of "dielectric material" aka pigeon s*it out).

Telescopes where the receiver is at the prime mirror focus and so facing the ground have much worse noise performance since there is always some sidelobe sensitivity from the ground at ~300K.

No idea off hand.

I expect it is related to the dielectric constant of green cheese.

Well if the -170dB is relative to the Tx power, this isn't that spectacular a radio.

It's a 34dB NF.

Typical spec's for a generic SA.

This one perhaps? The mode is called PAU43. PUA43 uses 43 tone FSK with adaptable very long-term integration.

I suggest you join the DSP-10 mailing list: Or, you could ask him. His email address is at the bottom of the first web page above.

You might also get some useful DSP info by joining:

Ummm... dB is a ratio. dBm is a signal level (above 1 mw into 50 ohms).

I know the feeling. I currently have a cold or flu. My mind is very boggled, which I presume means that it feels like it's stuffed with cotton.

Ultimate DX experience - Mars

Once you've "worked" Mars, you can move on to hearing the Voyager spacecraft: I use the calculations as a template for weak signal sanity checks.

Dunno.

One should always remember that EME records are two way contacts, in which case one station might be using a huge antenna (e.g. VE3ONT using the Alconquin 46 m dish) and a large transmitter power. Thus the other (your home) station can be quite low power with small antennas.

A few years ago, it was possible to exchange call signs (about 100 bits in an half hour period) with 100 W Tx power on VHF and a single yagi antenna at both ends with some advanced signal processing.

Unfortunately the Moon (even new Moon) is quite hot (more than 150 K), compared to the cosmic background (2.7 K) or the galactic background radiation in the Milky Way plane.

Receiving data from Voyagers etc. is "easier" at least when they are outside of the noisy galactic plane.

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I would suggest trying some rec.ham-radio groups.

?-)

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Pretty damn cool. This is a real lesson on how losses and SNR really work. 8dB SNR is getting rather difficult to dig out.

And to think that humans can dig out -8 dB SNR speech in a noisy room in real time. That's some impressive signal processing.

optics, etc.

Please remember with all these negative SNR claims (e.g. GPS), look carefully about the actual noise bandwidth. If the noise bandwidth is

However, the actual human bandwidth for speech is 3 kHz (telephony) or even less.

For GPS the real bandwidth (after despreading) is 1 kbit/s or for actual data extraction is 50 bit/s.

Thus, there are claims that the signal is usable at -xx dB SNR, when you chose the noise bandwidth accordingly :-)

With optics, we are talking about Poisson distribution and quantum efficiency issues. The quantum efficiency is quite good these days.

I have a TV on, I have WinTV on one computer, an internet radio streaming WSM, and reading newsgroups at the same time. I an keep all four of them separate. I need the multiple sound sources to mask my Tinitius.

On Wednesday, February 12, 2014 4:48:43 PM UTC-5, snipped-for-privacy@downunder.com wr ote:

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ngth at the receiver was -170 dB!

Yes thanks.Frankly, I am not versed in the BW-SNR-dB way of thinking, and I plan to study it more. In the case of the 1 watt, it was a bounce using a

Let me know, anyone, what the dB figure means and what it says about receiv ed energy. The dB definition says it is 10 x the exponent base 10 of a powe r difference. How would this relate to the return intensity i this case?

jb