Announcing OpenFHSS project (902-928MHz Frequency Hopping Modem)

I recently started an open-hardware project based on my RF work for the past several years.  Although I was targeting challenging real-time data collection in a tree-fruit orchard envrionment, UAV telemetry seems like a very good match for the design due to the inherent attributes of Low-latency and High reliability.  This modem is very similar to the performance characteristics of something like the original MHX910 from Microhard Systems.  Let me know what you think.

----------- from the project page ---------------


Project Development Site For Valhalla Wireless OpenFHSS. OpenFHSS is a community-based effort that includes schematic, eagle design files, BOM, gerbers, and firmware for a 902-928MHz ISM, 50-channel, FHSS frequency hopping spread spectrum modem.



  • High Performance, Long-Range Frequency Hopping Spread Spectrum Modem
  • Synchronous, Multi-Hop Repeater Chains
  • Ethernet Bridge Mode
  • Automatic, over-the-air firmware updates. Master updates all slaves simultaneously
  • 4uA MCU initiated sleep current
  • 2ppm stability for frequency and system timing reference.
  • Industrial quality enclosure, connectors
  • Real-Time Data Collection System with user defined scripts
  • LM3S6965 32-Bit Stellaris ARM-core MCU, CC1101 transceiver, CC1190 LNA/PA
  • Highly immune to multipath fading, interference
  • 5mS Channel Dwell Time
  • -107dBm sensitivity, 27.1dBm output power enables communications range in tens of kilometers. Depending on installation, ranges of >50km are easy to achieve
  • Applications include battery-powered data collection, Low-Latency Telemetry Links (UAVs), long-range internet communications. Quality Skype phone calls have been achieved with point-to-points links.
  • 230 kbps RF Data Rate
  • very low phase noise performance (see emc plots in images/emc_testing)

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3D Robotics
Comment by Chris Anderson on April 2, 2011 at 9:44am
Sounds very interesting! What your planes to produce prototype hardware?
Comment by Todd Elliott on April 2, 2011 at 10:13am

Hi Chris,

I have already been through the prototype phase and proceeded to have 24 machine built units produced.  Due to the small quantity, high quality of the manufacturing process, high-end connectors, these units were relatively expensive to produce as you can see from the BOM.   I'll attach a couple of images of the final product.

Comment by Marco Glattfelder on April 2, 2011 at 10:55am

What about 868MHz EU ISM?


Comment by Ed Stewart on April 2, 2011 at 11:25am
Keep us updated........
Comment by Todd Elliott on April 2, 2011 at 11:49am


It should be possible to modify the design to work at 868MHz.   First, you would need to change the Fujitsu 902-928MHz band pass filter to a filter centered around 868MHz.   Firmware would also need to be changed to operate the transceiver in accordance with the EU regulations for 868MHz ISM.   Other than that, it should work just fine.  Might need to tweak a few components and the antenna, etc for optimal operation.  One of the nice things about open designs is that someone with experience in EU regulations can jump in and help modify the design for EU compliance.

Comment by Jack Crossfire on April 2, 2011 at 11:58am

Let us be the 1st to request a data rate over 1 megabit, since the need for higher bandwidths has been ranted about in many a past blog post & 256kbit is easily achievable with $2 FSK chips.  The reason people want higher bitrates is for HD video.  1 idea is to gang together multiple transceivers.  The added value would be synchronization done in your product.

Comment by Todd Elliott on April 2, 2011 at 12:09pm


230kbps is very close to the maximum data rate possible for an FSK, 50-channel, high power frequency hopper due to the 500khz channel bandwidth requirement in the FCC regulations.  To achieve higher data rates, you will have to resort to 26MHz DSSS or much lower power levels (like zigbee) to keep the power spectral density below 8dBm in any 3khz band width.  In any case, performance will be significantly degraded by designing for a higher RF data rate.

Comment by Bill Porter on April 2, 2011 at 3:40pm
Maybe i'm blind but I can't find a BOM. What is the cost to build these?

At those specs especially 500mW, this seems like a real competitor to some of the commercial products.
Comment by Todd Elliott on April 2, 2011 at 4:08pm


The BOMS are located under openfhss/vikingXE_hardware/bom

I see now that I included cost columns for PCBA BOM, but I didn't include cost for the final assembly BOM.  For reference, my cost to build 24 units minus adc calibration and testing was app. $330 USD each.   That did include x-ray inspection, and final assembly.  The manufacturer I use is very high quality production:   Their #1 priority is quality in manufacturing.  I have 21 units in stock and can sell them for $794.39 each.  I realize this is a relatively high cost for hobbyist endeavors, but that is the reality.  By opening this design to the public,  it is possible to get the cost down by not including the enclosure, connectors, etc.  Changing the RF design,  however, may result in degraded performance.  I put a lot of effort over several years to arrive at this design.  As you can see from the images/emc_testing plots, this is a high-performance design.  For comparison,  competing systems from Microhard, Freewave are going to be in the $1500 USD range.  They are not open designs.

Comment by Bill Porter on April 2, 2011 at 4:23pm

'Your cost' to the selling cost (330 to 794), what causes the jump? Did you mean "That did NOT include x-ray inspection, and final assembly"?

I'm curious to see where your design goes and if it gets picked up for regular production. I work for the U.S. Navy building Unmanned Systems, and we always use Freewaves. We get 1 Watt 900s for about $1100 because Freewave wants to keep us as a costumer.

I would like to see the money spent on supporting open source products like this, though it's tough to replace 'mission proven' hardware with new designs without just cause. Thankfully there's new regulations we have to follow were bids must go to 'disadvantaged business' (the PC way of saying small businesses) whenever possible and doesn't compromise product performance.


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