Project Echoloon: A Small, Open Source, Cross-Band Repeater Board for High Altitude Ballooning

I had an idea to do this on a long drive back from a friend’s wedding. As far as I know, there isn’t a lightweight single-board  [removed 10/11/16] solution for a crossband repeater for high-altitude ballooning. If there was, we’d be hearing about it a lot more. We would have contacts via balloon along with via satellite. I aim to develop something cheap and easy to build, and maybe at some point get someone to mass-produce and develop the project further.

[Added 10/11/2016]: I also just really wanted to write this down so I could sleep at night instead of thinking about this idea, to practice writing requirements, which is a day job thing I do sometimes, and to keep my skills up with electrical projects and development, which isn’t usually a thing I do in my day job.

This has been done before, but not in a very thorough manner. I’ve searched google for high altitude balloon, and found a few things, from a crossband repeater on EOSS’s site, to student senior design projects, and a few other projects here and there, but nothing as organized or mass-produced as it can be. Basically, I would like to take the current APRS high-altitude balloon digipeater and beacon hype and turn it into a crossband repeater high-altitude balloon hype and make a sort of special operating event, contest or award scheme out of it just like today’s ham radio satellite communications.

This isn’t yet a completed design, it’s more like my personal notes on the project. It’s in active development, and it may never be complete – I’m a busy person with a busy life, and I certainly don’t have the time now to devote to it, but hopefully either soon I will, or someone with the time will take it and run with it, so long as open source design practices are followed. You can certainly make and sell the project commercially, just please keep it open.

For those interested in traceability, this is the first release of any information dealing with the project. If it gets momentum, I’ll put it on Github. Edits to this page will be denoted by <thing added> [added <date>]or <removed thing> [removed <date>].

I shall call it Project Echoloon. Not to be confused with Name subject to change lol.

Project Echoloon

Project Echoloon is an Amateur Radio cross-band repeater device that can be lifted by a few helium or hydrogen-filled party balloons. It will also contain an APRS transmission capability so that users can be somehow notified that the repeater is in the area, to know exactly where to point antennas at, and to allow it to be easily recovered. It’ll be very low power so it can operate during several minutes or hours before the balloons burst and the device falls back to earth [added 10/11/16] within recoverable range.

It’ll be powered by a small Li-Ion or LiPo battery and possibly a small array of solar panels. It should allow for at least 8 hours of operation during good sunlight.

It shall be cheap – no more expensive than a Baofeng. In fact, it’ll probably use the same RF chips that are in the Baofengs and other chinese radios. It will have adequate filtering too. $25 is my first guess for an initial price. I’m not doing this for a profit until it’s in a manufacturer state.

It should be recoverable too, being tracked by APRS and having a transmitter to radiolocate. Once it’s impacted, a strobe LED will also blink and an audible alarm will go off. We could even put a Tile on it or something for the last 100ft.

I think a parachute adds too much weight and the device will be light enough so that if it falls at terminal velocity it won’t be damaged. It’ll go in a small foam case to help thermal stress, help cushion its impact and float if it goes in water. It should not be allowed to go too far so that A.) it doesn’t go out of the country and B.) you don’t have to drive too far to recover it. It could be modified for circumnavigation at some point, but it’d have to have a lot more logic to stay legal in every country it may be over.

The design, software, hardware and documentation will be open source. I hate closed source projects in ham radio with a FIERY PASSION. It’s cool you want to make a buck, but you can still make a buck making stuff open and freely available for anyone to improve it or build it themselves. That’s the spirit of ham radio.


  1.  Function(s)
    1. Simulcast half-duplex voice FM repeater
      1. Echoloon (herein referred to as “The Device”)shall receive FM voice signals from 2m band, and simultaneously re-transmit them on 70cm band OR vice versa
        1. Need to do a trade study between TX/RX bands. APRS beacon may favor transmission on 2m band whilst power requirements may favor UHF band for use with high-gain antennas.
      2. The device shall not interfere with any other repeater or satellite repeaters i.e. frequencies must be coordinated.
  2. Control
    1. The Device shall be remote-radio-controllable on an unpublished frequency.
      1. The Device shall receive DTMF codes and convert codes into control input.
    2. In the event of interference caused by the device, The Device shall be able to disable transmission functionality via a DTMF command. [FCC CFR §97.109(d)]
  3. Identification [FCC CFR §97.119(a)(b)(1)]
    1. The Device shall announce its FCC callsign in 20WPM CW every ten minutes.
    2. Every thirty minutes during positive climb or level flight, The Device shall announce “This is Project Echoloon – a high altitude balloon crossband repeater, currently at <height> feet over gridsquare <6-digit gridsquare locator>. Please use <input frequency> megahertz with PL <PL tone> hertz.
  4. Size, Weight and Power (SWaP)
    1. Size
      1. Circuit board shall be 2″ x 3.5″
      2. PCB material shall be two-layer FR4, 0.031 inch thickness.
    2. Weight: The Device shall be capable of being lifted by a number of common party-style latex or mylar balloons. Weight not to exceed 50 grams.
    3. Power
      1. Trade study on battery and solar panel configuration
        1. Battery only
          1. Short duration
      2. Solar only
        1. Not enough power, especially in clouds
        2. Very light
        3. Complex circuit design
      3. Both Battery and Solar
        1. Longer operation
        2. Heavier and more complex circuit design
      4. RF Power Output not to exceed 50mW
  5. Flight
    1. The Device shall be capable of being lifted by common helium-filled party balloons, either latex or mylar.
    2. The device shall be capable of reaching maximum height of 100,000 feet, then bursting.
      1. Upon bursting, the device shall go into recovery mode, where APRS begins to beacon more frequently (see recovery).
  6. Cost
    1. The Device shall be affordable to everybody.
      1. Material cost shall be less than $25
  7. Tracking & Recovery
    1. APRS Beacon
      1. The Device shall transmit its GPS position and a message containing repeater input/output frequencies, device name, and website on the APRS frequency.
      2. The Device shall share the same RF transmitter and antenna to transmit the beacon packet
        1. This will cause a temporary outage of repeater functionality that is not detrimental to its use.
      3. The device shall beacon it’s position every 5 minutes during ascent
      4. During descent, the device shall beacon it’s position as a function of altitude: less height = more beacons.
        1. Beneath 5000ft altitude during descent, APRS path settings shall change to WIDE-2 to make use of digipeaters with greater hops for recovery.
    2. Alternate Modem?
      1. [Added 10/11/16] Unit shall be capable of interfacing with other devices (such as a integrated APRS tracker/data radio) through USB/UART/Serial/I2C/???
    3. No parachute shall be required.
      1. This device will fall at terminal velocity but be protected from impact and thermal stresses by being enclosed in a small foam case.
    4. Post-descent recovery
      1. Upon impact, the Device shall transmit its FM CW ID and a 3 second tone every 30 seconds on it’s published repeater output frequency for RF direction-finding.
      2. The device shall have an audible buzzer and bright strobe LED for locating.
      3. The device shall have contact information written on it.
  8. Licensing
    1. The Device shall be open source.
      1. Hardware shall be licensed under the TAPR Open Hardware License
      2. Software shall be licensed under GNU GPLv3 License
      3. Documentation (including these requirements) shall be licensed CC-BY-SA-4.0. See below.
    2. I don’t know how to properly “license” anything so help shall be given to Sterling on how to do this. Regardless, I don’t care how it ends up but I do not want it to end up in someones hands as a closed-source for-profit project.
  9. Hardware and Software Development
    1. The Device shall use freely available or open source tools for schematic capture and PCB layout such as Cadsoft Eagle Express or Kicad.
    2. Hardware and software files shall be hosted on a public Github page.
  10. Mechanical Design
    1. The Device shall be encased in a small foam block to aid in thermal relief and prevent damage upon impact.
    2. Antenna
      1. Linear or circular polarization?
      2. Wire, dipole, rubber duckie, cloverleaf?

You’ve reached the end of my work so far. Stay tuned on the N0SSC twitter and this post, and soon a GitHub page, to be created.

To do:

  1. Finish requirements
  2. Power source trade study
  3. Research RF system-on-chips and filter designs
  4. Find a volunteer embedded ARM developer or figure out how to do  arduino or something…
  5. Discover how difficult or expensive 90% of these requirements are, and then remove them lol.
  6. Finish Requirements
  7. Develop BOM
  8. Develop schematic
  9. Develop layout
  10. Send to OSHPark for first prototype
  11. Fix problems
  12. Get second prototype with hopefully zero problems
  13. Burn through any money and time I had finalizing the product
  14. Marketing for interest-gathering
  15. Crowdfund $1500 or so, something modest
  16. Fund run of 50 boards
  17. Build them after 4 months of delays and parts stock issues
  18. Ship to backers.

Sorry this numbered list is gross, I don’t know CSS or HTML enough to make it look pretty.


Creative Commons License
Project Echoloon by Sterling Coffey, N0SSC is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Based on a work at



Author: N0SSC

25 year old amateur radio operator. I love everything about ham radio. Trying to learn CW and contest more, and doing my best to promote youth involvement and retention in this aging hobby.

Leave a Reply