Foundations of Amateur Radio QRP EME project update #1 Over the past year and a half I've been working on a secret project. Today I'd like to share what I've been up to. To set the scene, I'm not doing this on my own, a fellow co-conspirator is Randall VK6WR who became an amateur about 20 months ago. Randall has a long association with the Engineering Development Array and the Murchison Wide Field Array, two of several radio telescopes that are built on one of the few radio quiet areas in the world and located near the future home of the Square Kilometre Array, the SKA. One day Randall and I started talking, as you do, new amateur, new topics, interesting new fields and ideas. We hit on the idea that radio astronomy telescopes are able to receive 2m signals. This started a discussion about using a radio telescope to receive a moon-bounce signal. So, the idea was born. Can we create a 5 Watt signal, bounce it off the moon and have it be heard by a radio telescope? Randall and I have been working on that on and off since our first discussion. Let me start by pointing out that we've not managed this yet, but we think it's a project worth doing, to forge cross skill exploration by various different groups. I have a strong background in IT and a few years as a radio amateur; Randall brings with him a wealth of radio astronomy engineering expertise, not to mention signal processing, communications and myriad other skills. We started to do this on the quiet, why talk about something that hasn't happened, might never happen, could be done by someone else who'd claim the glory before we did, and so-on. I've come to the realisation that while those things all hold true, this is a non-trivial project to achieve and anyone who puts in the work and gets there is welcome to claim the glory. So, in the 20 months gone by, while both working full time we've done lots of things. Let's set the parameters. When we first started, both of us were holders of an amateur foundation license. This means hand-keyed Morse, 10 Watts and band restrictions. Because I'm me, I decided that the difference between 10 Watt and 5 Watt wasn't significant enough to make or break this, so we went with 5 Watts QRP. Our license precludes the use of WSJT modes, invented by another radio astronomer, Joe K1JT, so the signal had to be something else. We settled on a manual slow Morse signal. We're using a radio telescope at one end, so it had to be on 144 MHz. Those decisions made, our first project was to attempt to calculate if we could actually achieve this. Conventional wisdom says no, but our ongoing calculations revised several times since our original effort, show that we're right at the edge of what is possible. We then started the process of determining if the radio telescope could actually hear moon bounce radio signals. We have a limited field of view, roughly 20 degrees around vertical, so the moon has to essentially be above the telescope. The galactic centre is a very noisy place from a radio perspective, so it has to be at least 20 degrees away from the moon. Similarly the sun, also very noisy, needs to be 20 degrees away from the moon. That started a process of me learning Python, so I could use Astropy to create a table with observation times that match those criteria. I'm still working on that. Having been a programmer for 35 or so years, I'm not a fan. We did some manual calculations to do some test runs and had two amateurs send a signal to the moon, which for several reasons, we were not able to detect. Traditional Earth Moon Earth, EME, communications benefit from ground gain, something like 3 to 5 dB of gain based on the path essentially ducting across the earth, but that requires the moon to be near the horizon, so not relevant for our project, since the moon needs to be overhead. Of course, it might mean that I need to travel half-way across the globe, so I can get the gain, but that's another project for another day. We get some effective gain from having a very stable signal. You might recall I purchased a high stability compensated crystal module, a TCXO, for my radio a while back, this project is why I did that. Another thing I purchased at the time is mechanical filters which also provide a little effective gain. We started the process of acquiring some high gain 144 MHz Yagi antennas, but through some miscommunication with the amateur who was selling them at a really nice price, we missed out and haven't yet bit the bullet on another set. Initially when Randall and I started this, we were working on it on our own, we tried to learn as much as we could and test the waters ourselves. We've been at it now for a while and it's become apparent that this is going to be something that is likely to involve several other amateurs. Some have already been helping, Allen, Allan, Keith, Alek, Leigh and Marcin all contributed time and material. No doubt this list will grow as the project continues. At the moment I'm still trying to write code to create a calendar of dates that will suit the radio telescope with the restrictions we have in relation to the moon, sun and galactic centre, so we can actually prove that the telescope can hear an amateur radio signal. We'll need to source some high gain antennas, likely more than two. Once we've done a one-way test, that is, me sending and the radio telescope hearing, we'd like to do the same but between two QRP stations. No doubt the road ahead is paved with spikes, potholes and road-blocks, but as adventures go, this one has been sustaining me for nearly two years and so-far it's showing no signs of abating. I'm Onno VK6FLAB To listen to the podcast, visit the website: http://podcasts.vk6flab.com/. You can also use your podcast tool of choice and search for my callsign, VK6FLAB. Full instructions on how to listen are here: https://podcasts.vk6flab.com/about/help All podcast transcripts are collated and edited in an annual volume which you can find by searching for my callsign on your local Amazon store, or visit my author page: http://amazon.com/author/owh. Volume 7 is out now. Feel free to get in touch directly via email: cq@vk6flab.com, follow on twitter: @VK6FLAB (http://twitter.com/vk6flab/) or check the website for more: http://vk6flab.com/ If you'd like to join a weekly net for new and returning amateurs, check out the details at http://ftroop.vk6flab.com/, the net runs every week on Saturday, from 00:00 to 01:00 UTC on Echolink, IRLP, AllStar Link and 2m FM via various repeaters.
It's not an 'adventure', its 'physics'. IMO, this is a foolish enterprise that indicates profound absence of knowledge of the basic physics. The fact that you didn't walk us through it is really an insult to the many hams who understand moonbounce, and radio astronomical techniques. Your knowledge of the Friis equation, and 'target illumination' is disturbing. On CW, your choice, you simply cannot make up for -25+ dB compared to conventional QRO installations, at 144 MHz. And if you use Murchison for higher RX-end gain, you will under-illuminate the target. Breaking it into sub arrays and post-observation averaging is really not a 'contact'. Post- observation pseudo-coherent averaging won't buy you the QSO. You will need to do so much correction for Doppler over the long time average that it really questions what exactly is the point. Elsewhere you have told us to 'forget the physics' when it comes to antennas. That's really unacceptable, and this is an excellent example of what happens when you do so.
VK6FLAB said-- "Without going into the physics of the how and why..." at: http://forums.qrz.com/index.php?threads/how-do-i-get-a-better-antenna.637731/ We live in a deterministic universe. A great accomplishment of the species is the ability to build a knowledge base and understand it and its governing rules, known as 'physics'. Before we proceed in ignoring that knowledge base, and rules, it behooves us to understand the cost and the risk of that enterprise.
I don't perceive any insults. I applaud you for undertaking the idea. This is a great way to gain knowledge through solving a practical problem. There is no mystery here or any unique solution for you do 'discover'. Boiled down to basics this answer will be found in a link path budget. Put in the gain and loss number numbers for each piece of equipment, the path, the moon, and the answer will be a figure in black in white. You can't cheat the physics, no matter how clever you are. No need to buy antennas, scrounge parts, etc. trying to sneak up on a contact. This isn't HF with highly variable propagation. With EME you either have the excess power for contact or you don't. Keep up the project. EME is worthwhile as is your gaining of knowledge. In the end I believe you will find you would need to use a massive transmitting antenna array (probably beyond all practicality), given your limited receive antenna capability and chosen power level. The easiest solution will be to build a practical transmit antenna array and use more input power. Again, a few minutes of calculation with a link budget will tell you precisely the antenna gain and input power required. Good luck with your project! Bill
IOW, go back to step zero--- that is check the physics--- and don't do QRP. Again, gain does not buy you anything (or very little) if you underilluminate the target. Your gain goes up but your RCS goes down.... VK6FLAB wants us to DO stuff without understanding what goes into it. To wit: "Without going into the physics of the how and why..." No one says you have to know diffraction and Cornu spirals, but a certain basic level---much of it in the actual ham exams in the US-- is required. If you find the physics tell you it WON't work, you have TWO options: A) Try some other interesting project (with a priori knowledge of the physics); B) Ask what assumptions went into the physics and ask if there are other --physically viable-- ways of getting around it. B) is OFTEN the path to new innovations. 73 Chip W1YW
You are doing everything the hard way. This is well trodden ground. Most fundamental, do you know the radar equation? Look for VK3UM EMECalc, download it and use it. On 2m EME, 200W and 1 long yagi is QRP. Chip didn't mention it, but look up target illumination. The big dishes have enough gain but will only look at a small spot, not the entire disk of the moon. Read the ARRL Handbook chapter, Space Communications. Oh and get the source code for WSJT, you want the astronomical data window. You can use that and WSJT CW mode within your license privs. Sheesh.
If he doesn't get the Friis equation and mirror illumination (RCS), then doing a second bounce to get him the radar equation is way beyond him...:-( BTW, I did mention target illumination... 73 and HNY, Chip W1YW
I was wondering earlier in the thread how the 240 db +/- path loss was going to be made up with 5 watts Tx power! I don't doubt the Rx system can hear 'a signal' but you have to get it up there first to be reflected back. Even then it is spread out and phase reversed. It's like spitting in the wind and trying to detect it 10 seconds later a half a world away.
Onno, I have to congratulate you and Randall for thinking up this effort but want to ask why are you limited to a Foundation License? What is the upgrade path? Can you get an experimental waiver to use one or more of the JT modes? As one who was present, as a helper, aka gopher, 18' Kennedy dish mover, etc at the W1BU 1296 MHz EME site shortly after the historic first 2 way EME I have followed a lot of the development over the decades. I made many trips from Arlington to Medfield MA with Jack Wilson, W1QXX, who defied the laws of physics with his wild driving! I never had an EME QSO but have heard my own 2M echos with 1500W and a pair of long yagis at the horizon but never got interested enough to add it to an already busy life back then. Carl
While I agree that QRP EME is going to be difficult.... I don't see it as impossible. I've spent quite some time working with Amateur Radio Astronomy and have done a little SETI research. If you run the numbers, you will see that the bounced signal will indeed be tiny, but it will still be stronger than those from Voyager a few years ago. Those signals were being heard by some of the larger radio telescopes. I do have one suggestion though: switch from 2meters to 70cm. At 70cm the Earth's atmosphere is virtually transparent. At 2m this is not the case.
There is one BIG difference between a signal received from Voyager and one reflected of the surface of the moon. The signal from Voyager is all in phase, just weak. The signal coming back from the surface of the moon is not in phase, because the moon is not a smooth surface. Rege Edit: brain teaser, suppose you have a antenna with enough gain (narrow beam with) so that the entire signal "hits" the moon. Would you receive a stronger, weaker or the same signal to noise from the light side, or the dark side of the moon, and why? Rege
