Step 2: The Radio Communications

Radio communication is a difficult thing on Planet Earth. Radio waves won't travel through water or dirt very well (this includes hills and plants). To keep communication with an object you typically need "line-of-sight." The further away from an object you get the larger window you need to have line-of-sight. This is what's known as the Fresnel zone (http://www.afar.net/fresnel-zone-calculator/). Luckily for us the balloon flight will be high in the sky and the only challenge will be staying close enough to the balloon's ground position to have line-of-sight when it lands. If you aren't close to the payload when it lands you may have to search a long time to find it because you won't have the exact GPS location of where it landed.

My last balloon used the XTend 900 radio module from Digi (http://www.sparkfun.com/products/9411) as the main communication system. This 1 watt, 900 MHz radio allowed me to keep communication with the payload for the entire flight while getting flight data updates once every 5 seconds. The XTend 900 can interface to the XCTU configuration software to change the serial data rate in a user friendly GUI way (http://www.digi.com/support/productdetl.jsp?pid=3352&osvid=57&s=316&tp=5&tp2=0).

On the PC side of things you need to connect the XTend 900 to the PC's USB port. The best way to accomplish that is to get the uUSB-MB5 USB to serial converter from 4D Systems (http://www.4dsystems.com.au/prod.php?id=18) and the XTend breakout board from Sparkfun (http://www.sparkfun.com/products/9596). Solder the breakout board onto the XTend 900 or buy the proper connector. Then solder wires from the uUSB-MB5 to the breakout board in this order:
-uUSB-MB5 RX to breakout DO
-uUSB-MB5 TX to breakout DI
-uUSB-MB5 GND to breakout GND
-uUSB-MB5 +5V to breakout VCC
-On the breakout board you will also need to solder a 10k resistor between SHDN and VCC.

The balloon payload is similar and you'll need another breakout board to make things easy. Solder between the GS407 and XTend 900 breakout board like so:
-GS407 RXD to breakout DO
-GS407 TXD to breakout DI
-GS407 GND to breakout GND
-GS407 VCC to breakout VCC
-On the breakout board you need to solder a 10k resistor between SHDN and VCC

We almost have a fully functional radio link between the GPS and PC. Keep going to the next step to fire it up!
<p>Hello,</p><p>Is there an easier/cheaper way to retrieve the location of my payload if I don't need to know its location at high altitudes? (If I only know it's location at the begginingg and end of the flight?)</p><p>Thanks,</p><p>Joey</p>
<p> Hi, great work. I am curious that if I need to get a HAM license for the XTend 900 radio modules?</p>
You probably guessed by the title that you don't. 900 MHz is in the ISM (industrial, scientific, and medical) band. This is an unregulated frequency. The down side is that someone else with a higher powered radio may interfere with your transmissions. The XTend 900 uses spread spectrum, so you should be able to receive no matter what.
<p>So I don't need to get a license, right? But why doesn't it need a license? just because that spread spectrum won't influence other wave bands?</p>
You don't need a HAM license. As to why...it just isn't required. Has nothing to do with spread spectrum.
<p>I am very appreciate about your assistance. A simple question, I saw other people who launch HAB usually use Arduino or Raspberry Pi. Why didn't you use them?</p>
Since this design only needs to transmit the GPS, there is no need for an extra processor. If you want to add on sensors and transmit that data, then you will need to read all sensors into a processor and compile a serial data stream to send over the radio. Launching and recovering a balloon is much more difficult than you expect. Be sure you take your time and do your research. It's very deflating when you lose a $500 payload because of a silly mistake.
<p> I am very interested in HAB, and I really wanna launch this thing. So if there is personal email or something else that I can contact with you? I may encounter some problems in the future when I make my own design.</p>
<p>and I don't either get a license from FAA as long as I make sure the weight of the payload is below 8 pounds?</p>
There are some rules about unmanned balloons in the FAA regulations. I can't give you the answer for your particular situation, but typically a balloon under 8 pounds with a tether that breaks at 50 pounds pull does not need FAA approval. Be sure you do not launch or land within 5 miles of an airport, and you should file a NOTAM report. You can google search for the NOTAM hotline number in your region
<p>So the GS407 is now discontinued. Any alternate advice you might recommend? I assume hookup will be different as well... Great work by the way!!! </p>
You'll have to do your homework on this one. The U-blox chipset allows you to get position above 60k feet. That's really the only thing you need to find in the new GPS receiver. Good Luck!
<p>Hi, great ible. Quick question: I am wanting to have a photo stream transmit to me from the balloon during flight. I am very new to this area, what do I need for that? I assume I can't just hook up a camera to the breakout, I need to connect it to a Pi or Arduino. Also, what is the point in having the radio module on the ground? You are not transmitting TO the balloon, so all you should need is just a receiving antennae....</p><p>Help is greatly appreciated, thank you. </p>
I give the same advice to everyone doing this for the first time. Keep it simple, or you'll lose a lot of expensive equipment. Balloons seem very simple, but you'll be panicking on launch day. Launch your first balloon with just the tracking information coming at you. Once you can track and find your balloon on the ground, then move on to multiple data streams.<br><br>When you get to trying to transmit the picture, you'll find you need to convert the picture to a serial data stream. That is going to be a lot of data, and the data rate you get over a 40+ mile radio link is very slow. You're not going to be getting real time video or more than a picture a minute with inexpensive radios. Do your research on picture formats and baud rates. A little math will tell you just how long it takes to transmit a picture.<br><br>As for having a transciever on the ground, it was easy to write the firmware once and use the same module on the balloon and on the ground. Keep it simple, reuse known equipment and code, things will fail on launch day, and with some luck you'll find your first balloon.
<p>I am running through these links and I have come across a bad one. Is there a website that I can be directed to instead of </p><p>(<a href="http://www.4dsystems.com.au/prod.php?id=18" rel="nofollow">http://www.4dsystems.com.au/prod.php?id=18</a>)</p>
<p>That tracking software you use it is accurate? I am North West of you in Southern BC. I have played around with this other website but it gave me a completely different flight path from the one that you use. I figure if it is accurate for you it should work for me here too. <br><br>Thanks. <br><br>Great instructable!</p>
I found their prediction to be right on the money. What wasn't on the money was my ascent and descent calculations... The balloon ended up traveling twice the distance over ground because the ascent rate was half what I planned for.<br><br>Wind patterns at different elevations and different locations are extremely variable. You should run predictions right up to your launch date just to see what might happen if something changes.
<p>Good to know. Any suggestions on adjusting for the ascent rate? Don't want to get caught in the mountains before I clear the valley bottom. </p>
<p>My ascent rate was 16.5 ft/s, which seemed to be half of what the prediction expected. If you can't get your balloon to the 33 ft/s that the model expects, then you should find a different predictor that you can adjust the ascent and descent rates. It's always good to get a second opinion, so using two models from different sources is a good idea anyway.</p>
<p>Thanks again. </p>
Also would the RFD 900 Radio Modem work instead of the xtend 900? <br>http://store.rfdesign.com.au/rfd-900-radio-modem/
Looks like a good radio. I haven't used the RFD900, though. It has enough output power and TTL serial interface, which are the most important things for this application.
I have this for my gps would this work work instead of the GS407?&nbsp;<br> <a href="http://www.makershed.com/Ultimate_GPS_Breakout_V3_p/mkad47.htm" rel="nofollow">http://www.makershed.com/Ultimate_GPS_Breakout_V3_p/mkad47.htm</a>
The description says it has been tested up to 88k feet altitude. I can't say for sure that it will work, but it seems like that should do for you.
Hello, I'm slightly confused as to which parts go onto the payload and which stay on the ground. From your descriptions I got: <br>Payload <br>- 1 GS407 <br>- 1 breakout board w/ resistor <br>- 1 battery <br>- 1 antenna <br>Ground <br>- 1 XTend 900 radio module <br>- 1 uUSB-MB5 <br>- 1 breakout board w/ resistor <br>However, the numbers don't match up and I can't seem to find where/how the second XTend 900 radio module connects. Any mention of the XTend 900 radio module only refer to it being connected to the PC. Could you please clarify? <br>If I follow the numbers you give in step 9, would that would suggest that the second antenna is on the ground connected to the XTend 900 radio and the second XTend 900 radio is in the payload, connected to the antenna (by the way, does that connection need an adapter?) and the breakout board. Since the GS407 also needs to be connected to a breakout board, do they share one? <br>Thank you
Step 2 says that you need to solder the wires from the GS407 to the XTend breakout board. I assumed you'd know to plug in your second XTend radio to that breakout board. You'll have this set of connections when you're done: <br>Balloon payload: <br>-GS407-&gt;XTend breakout-&gt;XTend radio-&gt;antenna <br> <br>Ground Station: <br>-Antenna-&gt;XTend radio-&gt;XTend breakout-&gt;uUSB-MB5-&gt;Computer
Hey! Great tutorial but I was wondering- how could get immidiate data transactions? <br>If you live on a small island, it tends to fly into the sea :P Any suggestions will be appreciated!
There won't be a way to stop it from flying into the water, unless you plan on a payload that can fly itself back to you (this is illegal in the U.S. without impossible to get waivers from the FAA). <br> <br>You can increase the rate of NMEA messages from the GPS reciever to 5 per second on the GS407. Your best bet, if you must launch from an island, is to make your payload waterproof and buoyant. Do very careful flight plan predictions, fill your balloon precisely to get the rate of ascent right, pick your parachute for proper rate of descent, and get a fast boat so you can be at the landing zone before the payload lands. If you make the payload so it floats with the antenna facing up, you should be able to receive the signal well over a mile away from the payload. If the antenna is under water...you'll never hear from it again. <br> <br>Might be cool to make the payload an autonomous boat that drives itself back to the closest shoreline.
what was the peak altitude that your gps module was able to function at? Many of the devices I see on spark fun show that they have an upper limit of 18,000 ft due to COCOM regulations. Also the module you used is retired however there is a new model GS407, will the Airborne adjustment work on this new model?
The altitude measurements aren't actually limited by regulations and neither are the speed of movement...unless you plan on exporting your device outside the country (this statement is sure to get a bunch of comments from armchair experts). Using the dynamic platform setting of &lt;2G airborne for the GS407 I had, you can get altitude readings from ground to the maximum theoretical GPS altitude. <br> <br>With the new GS407, the setting is the same &lt;2G airborne, but it is no longer under the NAV section. It's now in the NAV2 or NAV5 depending on the firmware version you have. You'll still see the NAV, NAV2, and NAV5 sections with any firmware version, so the easiest thing to do is set it in all three. Then it's done and you didn't have to worry about reading out the firmware version.
How about an update on connecting the GPS with the new model GS407. It doesn't look like the same connectors are available to solder to? I'm pretty much electronically challenged, so figuring it out is way beyond me.
Ok, so it's a bit easier now actually. The GS407 uses a better connector and Sparkfun is offering cables with the connector attached. Get yourself one of <a href="https://www.sparkfun.com/products/9123" rel="nofollow">the cables</a>. Then clip off the connector that you don't need, strip the wires for TX, RX, VBAT, and GND. Then follow the rest of the instructions in this instructable using those wires. You can see the pinout of the connector in the <a href="http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Sensors/GPS/SPK-GS407A.pdf" rel="nofollow">GS407 datasheet</a> on page 4. Pin 3 -&gt; RX, Pin 4 -&gt;TX, Pin 6 -&gt; VBAT, Pin 1 -&gt; GND.
Dear NearSpaceLuke, <br>I am an AP Physics teacher. I want my students to do this as a class project. I will get all the materials then they will follow your instructions. Do you think 17-18 year old students would be able to complete this project? <br>Thanks in advance for your advice.
This is a good project for 17-18 year olds until the balloon gets in the air. Small balloons take about 4 hours to launch, track, and recover. The kids will probably get tired of waiting for it to land. If you aren't paying attention to the balloon and following it closely you may not be able to recover it.
Hello everyone. I've been researching and preparing for my first launch for weeks and recently have been scouting launch and landing sites. I'm working with the CUSF Landing Projector program now and have a minor question. When inputting my launch date, it already shows the date one day ahead of where I'm located now (I live in Florida ). I'm having a few issues converting EST to UTC time when it crosses over to the next day. For instance, if it's 9 pm here in Florida right now and I'm planning on a 10 am launch, what would I need to do. How far ahead will the program let me predict? Thank for any insight. <br> <br>** I'm just running simulations to get used to the program for now as I research and build my payload etc. I do seem to be able to run current simulations if I leave the date as it is and launch tiem by default.
In regards to the CUSF Landing Predictor, I'm following the step by step instructions I saw on this page and inputting my payload weight info etc correctly I believe. The projector y path and landing site look correct, but when compared to the wind directions I see on local Dopler it seems to be going to wrong direction. Is this normal, or am I doing something wrong. Local wind directions are out of the NE which I would think would make my payload travel SW. Thank you for any insight. <br> <br>Jason
Ok, so I apparnetly was not looking at the jetstream wind direction! Looking closer at my projected path, I now can see the lower level winds effecting the path correctly and then the upper level winds taking over. Learning more each day: <br> <br>Jason
If you're interested my new instructable on near space balloons is published! <br> <br>http://www.instructables.com/id/My-Space-Balloon-Project-Stratohab-Success-High/
Hi nearspaceluke<br><br>It would be great if you help me build the tracker. I am based in Australia and would love your input. <br><br>Up to it?
Here is a better site: http://nearspaceventures.com/w3Baltrak/readyget.pl
I actually don't like that site at all. The predictions come out just fine, but the user interface is garbage. The plot track to Google Maps never works, either.
That's the only one I use. It's usually VERY accurate. I've had it the prediction be off by less than a mile. I also like that you can look at the raw data and see lat., long. and alt. throughout the prediction (so I can compare it to the actual numbers during the flight). <br> <br>I also don't think I've ever had a problem looking at the prediction in Google Map.
Is there a reason why you are using helium, rather than hydrogen, as the lifting gas? I kinda thought that H2 would be cheaper, and provide more lift for the same volume balloon, but maybe there's some other reason, like maybe your local welding store won't sell you hydrogen.&nbsp; Just curious about that part, I mean your choice for lifting gas.<br>
Hydrogen is probably cheaper, and it is a marginally better lifting gas. It's also exponentially more dangerous than helium. Sellers in my area don't like to sell in large quantities to amateurs and the tiny bit of extra lift isn't really worth the added dangers in my mind.<br><br>However, I'm thinking about making a rockoon in the near future. The balloon would lift a rocket to altitude and then the rocket would shoot right through the balloon. It would be crazy awesome to see a giant hydrogen explosion as the rocket goes through the balloon!
Actually, the probability of it actually exploding is very high because Hydrogen is one of the alkali metals (not exactly.)
I wouldn't say the probability is high. It will burn. If mixed with oxygen it will explode. But for either of these to happen there has to be an open flame or a spark. Don't smoke and ground everything.
Remember what happened to the Hindenburg???
Yes, and remember what has happened to the dozens of other groups who do high altitude balloon flights and use hydrogen all over the country....nothing. A pencil is dangerous if you don't use it correctly. <br> <br>I've done five high altitude balloon launches (www.thetalon.smugmug.com/misc/space). If you use it safely, there's nothing wrong with using hydrogen. It's cheaper (a cylinder rents for $60. The same size helium is over $100) and it has more lift by volume. We are looking at doing a flight to break the altitude record in June. If we try it, we will be using hydrogen.

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