Posts Tagged ‘Satellite’
As I mentioned in passing yesterday I have a number of Arduino based projects buzzing around in my head. One of them is to produce a satellite antenna pointer/indicator.
I have used an Android AR tracking solution before (flaky at best) and can see the relevant information in Orbitron or SatPC32 to know where to point the antenna but it is difficult to see a PC screen when stuck out in the middle of the lawn!
My idea is this, I will make a large tripod to which I can attach appropriate antenna as I need, then during the satellite pass it has indicators to show where to point the antenna manually.
I envisage the azimuth indicator to be a large horizontal circle with 36 LEDs positioned at 10 degree intervals, the elevation will be a quarter circle with 20 LEDs positioned at 5 degree intervals. Then during the pass the appropriate LEDs will light and assuming I keep the antenna aligned to these I should in theory get the best signal... Crazy??
Yes I know I could make or buy an azimuth/elevation rotator, eBay is full of low speed high torque geared DC motors with auto-stop/hold and numerous software solutions exist to drive them but this would require a bit more engineering and isn't something I can easily fabricate at the moment. My contraption would be much more rustic being made of rough cut timber!
Bright LEDs are ridiculously cheap and controlling this number from the Arduino will require the use of multiplexer drivers. The popular ones are the MAX 7219/7221
I won't go into the details of exactly what multiplexing is, other than to say that each display element (LED) is driven one at a time but by switching the electronics at high speed combined with the persistence of vision make the viewer believe the entire display is continuously active.
This technique can be used for individual LEDs, an LED grid matrix, or for 7 segment displays. Last night I successfully got a MAX7219 based 8-Digit 7-Segment LED module working.
The next stage was to investigate how an Arduino could calculate the appropriate azimuth and elevation data. Thankfully a library already exists qrpTracker (code is here), within this library is a port of the Plan-13 algorithm first written in Basic by James Miller G3RUH in 1990, subsequently ported to C by Edson Pereira, N1VTN and further updated by Howard Long, G6LVB.
Plan-13 processes keplerian elements, time and (optionally) observer location, and uplink downlink frequencies; it outputs satellite latitude and longitude, azimuth and elevation, and Doppler shifted frequencies. At the standard 16 MHz Arduino clock speed, this code can complete these calculations in approximately 30 ms. This code is reported to be highly accurate, if provided with proper data.
The important data are the observer location (longitude/latitude) and the current time. Step forward my well used GPS module which once lock is achieved can supply that data.
The next is get the appropriate up to date Keplerian twin element sets (TLE) and extract the appropriate information from it and pass that data to the Plan-13 functions.
The standard TLE follows the following format
You need to extract the Epoch Year/Day (including partial data), Inclination, Right Ascension, Eccentricity, Perigee, Mean anomaly and Mean Motion for a calculation (drag/orientation aren't critical) For the moment I have just extracted this manually from the latest TLE and entered it directly into the program.
After just an hour or so of research and programming I have the LED displaying the current azimuth and elevation of the FUNCube-1 satellite (AO73) based on the current position and time derived from the GPS!
The first four digits is the azimuth, the second four the elevation.
Last week, I had lunch with an old friend, Bdale Garbee (KB0G). Bdale and I had both worked at HP for a number of years and we have been involved in some common ham radio clubs and activities. I followed the test and measurement path with Agilent Technologies when that company was formed, while Bdale stayed with the HP computer business. He is a recognized industry expert in Unix, Linux and all things open source. It is always cool to catch up with him and find out what he has been doing. He recently took early retirement from HP…I am not sure what “retirement” means for Bdale but its not playing shuffleboard at the retirement home!
Coincidentally, a few days later, I came across this video from HamRadioNow of Bdale talking at the ARRL/TAPR Digital Communications Conference. In this talk, Bdale discusses the general theme of making stuff and the satisfaction that is derived from that activity. It is about an hour long so grab a cup of your favorite beverage and take a seat.
By the way, check out the other HamRadioNow videos, especially the videos of the DCC technical talks. Good stuff!
73, Bob K0NR
I’ve had a mechanically completed SatNOGS ground station sitting in my garage in need of some care and attention for a while. Its just one of the projects that that I have filed under ‘ working but not very robust’. Essentially after I killed off the first driver board we have not managed to get it to drive properly (that is without smoke pouring out of motor driver’s).
Fortunately the SatNOGS gang have made it much easier to load up the client software on a RPi and run a rotator free ground station on the development site. So over the weekend I have produced a standalone set up in between going to the 2nd harmonics rugby festival under the moniker Ground Station 170
The set up is very simple get yourself a RPi 3, an rtl-sdr dongle and a simple antenna (I used this one which took all of 10 minutes to make) and have scheduled a few passes to see if it works. There is some info here if you’d like to have a go
If you have a few moments you can look at the other SatNOGS stuff such as the recently presented video.
If you’re like me and have been wanting to receive signals from ARISSat-1, it is pretty easy. Here’s is a simple way that you can do it in the field, with just something to record audio and a receiver that can hear the satellite on 145.950MHz.
Like many hams, I started trying to simply receive ARISSat-1. My first opportunity was today around 7 AM MT (1300z). ARISSat-1 was successfully launched (really tossed) from the ISS on Wednesday, 3 August. I blogged about these events which you can read here. While I have the Arrow satellite antenna from Arrow antennas, due to work commitments beginning also at 7 AM, I would be unable to go outside and receive the transmission properly. This meant my only real chance of hearing anything would be via my Diamond 2m/70cm vertical I have attached to the side of my house. While this solution is less than ideal, I should be able to copy some of the transmitted signals as the satellite passed overhead.
The 7 AM pass would be my most ideal opportunity with the setup I had available to hear anything. As you can see from the image to the right, the ARISSat-1 would pass just to the north of Denver metro area. By the way, the image is a screen capture of the iPhone app titled GoSatWatch. This app is available in the iTunes store for iOS devices (there is even an iPad version). The price is $9.99 and is well worth it if you enjoy working the satellites and don’t want to have to lug around a laptop everywhere you go. In my situation, I can’t easily work satellites from my QTH. I don’t have a large enough yard and trees and other houses are in the way. I drive up to a parking lot which overlooks Cherry Creek reservoir. From this position I can very easily operate the birds without trees and buildings getting in my way.
Again, I would not have time to drive up to this parking area and would only be able to hear what my vertical antenna was capable of receiving. My expectation level was set very low and just simply hearing a faint signal would have been considered major success. I had no expectation of actually being able to copy any audio or data/video. I had heard reports of other hams being able to hear via an HT and stock rubber duck antenna, so the wait began.
Around 1150z I turned on the digital recorder and just simply set it next to my Yaesu VX-6 hand-held transceiver connected to the outside Diamond antenna. I’ve used the VX-6 to listen to other birds before and have setup frequencies for some of the common amateur radio satellites. My interest in satellite operations has sort of come and gone over the last 3-4 years. I’ll admit I’ve yet to have an actual QSO via satellite. But have my process for receiving down fairly well. I do plan to try for QSO’s on AO-51 this weekend.
Anyway, around 1157z I began hearing faint noises in the static. I had the squelch open and from 1157z through 1204z I managed to hear both audio (female and male voice transmission) as well as SSTV tones. Thankfully the conference call just required me to listen and I sort of did this at about 50%. Most meetings never start on time and this one was no exception. By the time the satellite had traveled further south, the signals dropped and I shut off the recorder and turned down the squelch.
Once my meeting was finished, I listened to the audio recording and managed to pull out the “secret word” and I plugged the recorder into my Rigblaster and used Ham Radio Deluxe and DM780 to decode the SSTV data. The image to the left is what I managed to copy. I’m impressed, especially considering I wasn’t actually pointing an antenna in the exact direction of the satellite pass. Just about anyone with an external antenna can do the same thing. You just need to know when to expect the satellite and listen for it.
If you want to try your hand at listening for ARISSat-1 just set your 2m transceiver on 145.950 and at the very least setup an external antenna. At present time, ARISSat-1 is just slightly ahead of the ISS which can be tracked here. You might also want to check out Orbitron. Orbitron is PC software available to track just about any type of satellite orbiting the earth. I would expect ARISSat-1 to be added very soon. But just track the ISS and you should be OK for now.
Until next time…
73 de KD0BIK
Like so many fellow hams I follow on Twitter, Facebook and Google+, yesterday I sat glued to a small 6 inch window which showed the events unfolding up at the ISS (International Space Station) during the launch attempt of the ARISSat-1, amateur radio satellite. The 6 inch window was a browser window I had sized to fit in the upper corner of my screen so I could also still work.
I had heard of the ARISSat-1 launch a few days before and to be honest at the time I wasn’t aware of just how the satellite would be launched. The past few days have been busy for me at work and the assumption was it would blast into orbit on the back of a Titan rocket along with other payload. It really wasn’t until I began streaming the NASA channel (since Comcast doesn’t offer it) that I realized the event wasn’t going to be as “eventful” as I had first thought.
My morning started off busy like most and the spacewalk had already begun by the time I settled in to watch. The two Russian spacewalkers were already outside of the ISS with ARISSat-1 in hand. I heard mention ARISSat-1 weighs in at 70 pounds and appeared to be about the size of a toaster oven. At one point the satellite was un-tethered and perhaps moments from being launched when it became clear something was missing from the satellite. The missing item was the 70cm UHF uplink antenna.
This immediately caused a flurry of conversation on Twitter and Google+ regarding what happened to the 70cm antenna. Really unsure just how the ARISSat-1 arrived to the ISS, I tweeted “I wonder if anyone found an extra antenna in the glove box of Atlantis STS-135”. Others imagined it sitting behind some books or boxes on someone’s desk back on Earth. Of course, it could have easily been floating around in the ISS. We later heard an update which ruled out the missing antenna was on Atlantis as the ARISSat-1 arrived some time ago on board a Russian supply mission.
The launch of ARISSat-1 was the first of several projects to be completed during the EVA. The Russian spacewalkers eventually returned the satellite to the holding bay and started work on project number 2 which was to install a laser based communication system. The comedy of errors continued. At one point one of the two Russian spacewalkers either unscrewed a wing nut or was trying to attach a wing nut. It went missing and was then discovered floating off into the deepest, darkest depths of space. More space junk?
This little boo-boo spurred more chuckles on social media and the entire event sort of reminded many of us of a typical field day weekend. It also reminded me of the time I had left my house on a Saturday morning for a DAREC training meeting. We were meeting just a few miles away from my house and I was extremely early. So early that I realized I had my hand-held, but no antenna. I quickly returned home to grab the antenna and still made it to the meeting with time to spare. Of course…returning to Earth to pickup the 70cm antenna was out of the question and this was well outside of the scope of “What can brown (UPS) do for you”?
My morning soon turned into lunchtime and I had a 12:30 dentist appt. By the time I arrived back home it was a little after 2 PM. I checked in with friends on Twitter to learn they had launched ARISSat-1 successfully without the 70cm antenna. This left many of us on earth scratching our heads. I saw this posted on Google+ “It appears that ARISSat-1 was deployed…without the UHF antenna. My brain keeps saying WTF?”
While I (and many) found humor and poked fun at the events unfolding some 240nm above Earth, the brave men and women (regardless of nationality) are true modern day pioneers. The duties performed are as important as those performed hundreds of years ago by names like Columbus, Magellan, Lewis & Clark and two brothers named Wright. These duties are performed in an environment which very few could or would even want to journey. Thank you to all these modern day pioneers for what you contribute to the rest of us on Earth.
As I said, once I returned around 2:15 PM MT, ARISSat-1 was tumbling away from the ISS. I guess the decision to launch without the 70cm antenna was weighed against the next scheduled EVA wasn’t until February 2012. It was confirmed the missing antenna will have no impact to the satellites ability to transmit to stations on earth, and receiving capabilities will only be marginally impacted. ARISSat-1 was given a gentle push by one of the two Russian spacewalkers and it began its 1-3 month journey.
Hams all around the world began pointing their antennas to the sky in hopes of receiving the signals from ARISSat-1. Images like the one below slowly began making their way into social media streams. This one received by Peter Goodhall, 2E0SQL in the United Kingdom. This was a low elevation pass, but clearly shows the onboard cameras are active and audio was also received. Similar images and audio have been received by many other hams and will continue to do so for many weeks to follow.
If you would like to learn more about the ARISSat-1 Satellite and working satellites in general, please check out the AMSAT website. You might also find this document a helpful read. In the US, hams holding at least a technician class license can operate most amateur radio satellites with nothing more than a dual-band hand-held transceiver and an external antenna. There are many plans available on the internet (Google is your friend) on how to construct your own. Also, the Arrow II satellite antenna is used by many hams (including myself). Check out this link for this antenna and watch videos by Randy Hall, K7AGE. Randy also produces many other helpful “how to” videos and makes them available on his Youtube channel. Please check them out.
Until next time…
73 de KD0BIK