Welcome to the Issue #1 of the Radio-Sky Journal Since this is our first issue, I especially value your comments and suggestions. It will be difficult to make every issue of profound interest to every reader, still, I promise to strive to put something of value in each one. This issue is text only, to keep things simple. Future issues will include projects and graphics will be just about mandatory. In such cases, to see the project articles you will have to follow a link to a web page. If you have something which you would like me to consider for inclusion in a future issue of RSJ, please send it along and I will give it my sincerest attention. -------------------------------------- Contents: Feature - Interview with Ned Lewis Amateur Tip #1 Featured Radio Astronomy Website Radio-Sky Info Board Feature Implemented -------------------------------------- An Interview with Ned Lewis Our feature in this issue is an interview with Ned Lewis, an amateur radio astronomer who exemplifies the creativity and zeal of the prototypical amateur. RS. Before you began experimenting in radio astronomy, what did you read, and what were your sources of inspiration? NL. About four years ago I happened across the "Bambi" website ( http://www.bambi.net/ ). While the focus of the Bambi Project is SETI, what really caught my attention was that they had observed Cassiopeia A and a couple of other discrete sources with backyard amateur equipment. Before that day, I had not even imagined that it might be possible to detect any radio sources or even the Milky Way with amateur equipment. Right away, I read everything I could find on the internet about amateur radio astronomy and went to the library to get a photocopy of Darrell Emerson's "Radio Sky" article in QST and anything else I could find. Within a month or two, I ordered Bill Lonc's book. It wasn't long before I knew I was going to try it myself. I think the "Radio Sky" article (Ed. the QST article) and the 70cm observations at the back of Bill Lonc's book are the two things that made me think I might be able to do something similar myself. From the very beginning, what I really wanted to be able to do was detect the Milky Way and a few sources like Taurus A and Cygnus A. I read everything I could find about each of the brighter radio sources and visited used book stores looking for radio astronomy books. Cygnus A has a very interesting history in radio astronomy, and of course the crab nebula is a very famous super nova remnant with a pulsar and other interesting radio properties. One book that is quite good and is seldom mentioned is "Cosmic Radio Waves" by the Russian radio astronomer Shklovsky. RS. What is your electronics background? What would you recommend as essential electronics skills for someone who wants to begin experimenting? NL. I was a ham radio operator when I was a teenager ( WB6LIM ) but never gotback into it after I went away to college. So I already knew about Ohm's Law and resonant circuits and the basics. Several years before I got interested in radio astronomy, I built an A/D converter and some simple circuits to receive APT from weather satellites and WEFAX through a shortwave receiver. Typical for me, once I got it working really well, I pretty much lost interest. If nothing else, this hobby has taught me some things about myself that I did not know before! I am a computer programmer, and have tinkered with computer circuits quite a lot over the years. I don't have any formal training in electronics, but do read lots of books. Many people at the SARA conference are professionals and know much more about electronics than I do. In the past couple of years, I have learned quite a lot, and now most of my electronics are at least partly my own design. The more you build the more you learn! I still read lots of books and am always looking for new and interesting circuits. I think it is possible to start off by building simple circuits by copying designs in books. Some of the circuits in Bob Sickles "handbook" are fine. The more you can read about HOW a circuit works the better. After some time, you begin to know which parts of the circuit are critical or can be adjusted for certain purposes. A good book on Op Amps is probably a good idea. My main advice to a newcomer would be to focus on the basics. A well regulated power supply is a must. Many "regulated" power supplies are not nearly good enough for what we do. RS. You mention on your website that you do not have expensive electronics test equipment. What do you use and what would you recommend to someone getting started? NL. That is a tough question!. I miss having an oscilloscope, a good signal generator or a good calibrated noise source, and a sensitive power meter, but each of these items is only needed at certain points and I 'm not sure I would recommend purchasing them. I have managed to get by with just a good DVM and a scanner to generate harmonics on frequencies of interest. I guess it really depends on what you want to do! I make up for my lack of equipment by patiently and slowly adjusting things until they perform as expected. I remember you mentioning an episode with Bob Sickles and the resistor across the output of your diode detector. (Ed. Bob was able to diagnose an error with my first radiotelescope without ever seeing it. It was simply a bad choice of a key resistor value.) I don't know how much test equipment will help with that one... it seems too often be a matter of trial and error to balance the best change in signal with a reasonable stability. These days I adjust that value by seeing how much the signal changes when I turn the LNA on or off, and also by looking at observations of the sun. I also have over time built up a large collection of circuits, so that when I need this or that, it is usually either already built or can be constructed quickly. I have tended to take a "modular" approach, and this has turned out to be a good thing. I would definitely recommend building one thing at a time, and learning how it works. If your setup has 8 new untested circuits in it, and it doesn't work, then you have a lot to sort out! Try changing ONE thing at a time and seeing what the result is. Sometimes, there will be an improvement in one area at the expense of something else. For example, a TL082 chip is not too noisy, but has fairly bad thermal drift. RS. As an urban experimenter, you must face a lot radio frequency interference problems. What tactics have you come up with to minimize the effects of interfernce on your experiments? NL. Very true. In fact, I finally had to give up in the UHF TV bands-- even the cable for cable TV leaks. Moving up in frequency was a big step. Right now I have telescopes operating at 1.4 GHz, 4 GHz and 12 GHz. Even at these microwave frequencies, interference is a big problem from strong out of band signals. Also, the choice of antenna is very important. I built 4 different versions of the SARA quagi, and while I was able to observe the sun with them, the amount of RFI precluded detecting much else. Even if a sidelobe is "20 db down", it might not be good enough if the interfering signal is 60 db above what you are trying to observe! I have had the best luck with horn antennas... as the main antenna and also as feeds for dishes. Horn antennas do not let in much radiation from the sides and are relatively easy to build. I try to design the horn so that the -3db points are 1/2 way to the edge of the dish. I have tried a number of different kinds of dish feeds, and it is critical that they don't let in much noise fromthe sides. RFI isn't the only problem in an urban setting, the sun reflects off of nearby houses and structures and causes trouble too. At 70 cm, I ended up using a shortwave receiver with a bandwidth of about 15 KHz, but at least I was able to observe the sun with it! In some cases, narrow bandwidth can be a good thing. Even at 1.4 GHz and 4 GHz, I have to search around a bit to find quiet part of the band to use. My attempts at increasing the bandwidth ( currently both are about 30 MHz ) have always met with more RFI problems. At 12 GHz there is less of a problem. Right before I gave up on UHF I had been playing around with a couple of corner reflector antennas spaced about 55 feet apart. Looking back, I think those had a good chance of working well, and there were other things that could have been improved in my setup. Sometime fairly soon, I'm going to give them another try. RS. It appears you have tried radio astronomy on several bands. Which is your favorite and what frequency range(s) would you recommend for someones first experiments? NL. I enjoy all of them! 1420 has some advantages. It is high enough that you begin to get away from the worst interference, but low enough that the Milky Way and some of the brighter sources still produce a fair bit of energy. As for first experiments, it really depends on the circumstances. If you have lots of land in a rural setting, then it might be best to try 70 cm or even lower. If you live in a city like me, then I would recommend starting with 4 GHz or 12 GHz solar observations. I realize that this isn't as glamorous as Tau A or OH line observations, but you have a really great chance a success in a short amount of time. Also, you will needmost parts of the setup for any radio telescope, so why not learn how to build detectors and DC amps and get all your recording equipment ( A/D converter or whatever ) figured out while having the fun of actually observing something! RS. What has been your biggest thrill as an amateur radio astronomer? NL. Observing the sun for the first time was a thrill. There was also my first interferogram with definite fringes. The several weeks leading up to finally being able to make consistent observations of sources like Tau A and Cas A were thrilling.... I knew that I was close and the early results were noisy and drifty and I couldn't quite be sure if the "bumps" were real. At the time I was having some email correspondence with Bill Lonc and as he sent suggestions back and things were falling into place, it was a really exciting time. Every day I couldn't wait to see what had happened! I'll always remember the first scan of Tau A when there could no longer be any doubt. Meeting all the folks at Green Bank was really fun too. Many people from SARA took time to answer my questions and help me via email and it was fun to meet you all in person. I think one thing about this hobby is that I really enjoy it all the time. There is always a new project or something that can be improved. It is fun to try to dream up new things to try, and then actually try them! It seems the longer I do this, the more things come up that I want to try. I've been working with SARA member Kevin Finley, and it really helps keep my enthusiasm up. RS. If you were assigned the task of writing a motto for amateur radio astronomers, what would it be? NL. Well, for amateur radio astronomers like me, it would have to be: "Patience and Perseverance!" Visit Ned's great website at http://www.jps.net/ned/ra/ _____________________________________ The featured website is the PARI (Pisgah Astronomical Research Institute). If you haven't heard about this place please take a look. There are two 26 meter dishes, as well as others, being fitted for radio astronomy use. This used to be a government owned tracking facility. There is a strong leaning towards amateur involvement at PARI. They have occasional volunteer work weekends when you can visit the site, pull cables, and contribute your talents in many ways. This is a unique opportunity. Visit PARI at: http://www.pari.edu ______________________________________ Amateur Tip #1. When building temperature sensitive DC amplifiers, use high quality metal film resistors and only the best OP amps. My favorite OP amp is the LT1012. These devices are about $5 each from DigiKey http://www.digikey.com , but the extra cost is far outweighed by the better temperature stability you will achieve. A little less expensive is the LT1001 which is in the very good category. Both are pin compatible with the 741 (which should never be used in this application). RadioShack now sells a good variety pack of metal film resistors to get you started. _______________________________________ New Info Board Feature at Radio-Sky We have added a great new feature to our website. The Radio-Sky Info Board will be the new repository for help requests (non-order related) and discussions pertinent to radio astronomy. Post your questions here and search for topics of interest. Help a newcommer with your own experiences. Over time, the content of the new feature should grow rich with information. The info board URL: http://www.radiosky.com/discus ________________________________________ If you would like to unsubscribe to the Radio-Sky Journal, you can do so by visiting: http://www.radiosky.com/journal.html Simply, put in your email address and click the Unsubscribe radio button, then Submit. _______________________________________ Copyright 2000 by Radio-Sky Publishing website: http://www.radiosky.com snail mail: P. O. Box 3552, Louisville, KY 40201-3552 Journal commentary: journal@radiosky.com