Tuesday, January 19, 2016

Portable FPV Microwave Ground Station in a Backpack

A ground station is an enhancement to improve your video signal from your FPV aircraft.  There are a number of ways to build a ground stations depending upon your goals.  Two styles are popular, backpack builds and larger antenna trackers on tripods.  In my case, I wanted something portable, light weight, with everything I need for a few flights.  If you have built a multi-rotor or two you undoubtably stumbled upon Youtube videos about man packable ground stations.  This is a very simple to build project.  I doubt it offers the range of larger setups but it's great for my needs - park flying.  Quick list of the benefit if your not sure why such a pack could be helpful.

- Very portable: holds 3 flight batteries, 1 battery to electronics in pack, transmitter, aircraft, tools.
- Better FatShark FPV goggle battery life: I have the V1 which only includes a 1000mAh 2S battery.  After the 2nd flight my goggles are beeping low battery.  Moving to external battery reduces anxiety.
- Improved FPV reception: Duo Diversity receiver has two antennas and switches between the strongest signal for added safety.  I chose a high gain patch antenna for flying in front and a omni directional when I pass behind the pack.
- Handy access: plenty of room to carry transmitter, batteries, aircraft, FPV gear, extra props, hex drivers, etc.  Including place to carry tripod on the side, if you wish.  Hang pack from hook on tripod for extra distance.
Click to expand

Parts List
- Lowepro Transite Sling 250 AW (Camera backpack, BestBuy)
- 8" x 6" 1/4" Plywood
- ImmersionRC Duo 5800 V4 Diversity Receiver Race Edition (ReadyMadeRC.com)
- IRC 5.8GHz SpiroNET Omni-directional SMA Antenna Set (RHCP) (ReadyMadeRC.com)
- IRC 5.8GHz SpiroNET Patch Directional CP Antenna 13dBi (RHCP) (ReadyMadeRC.com)
- SMA Female to SMA Male RG316 Extension (15cm) (ReadyMadeRC.com)
- Misc: HTX battery connector, wire, heat-shrink tubing, solder, velcro Command Strips, 2 velcro 12" velcro straps, M3 screws, 2A circuit breaker/fuse(larger if TFT used), etc

I looked at several backpacks but settled on the Lowepro due to it's small size, adjustable configuration of the compartments, the pack sits flat on ground without falling over, and BestBuy had a deal at the time.  Some considerations, the pack must be room enough to safely stow a FrySky Taranis transmitter, 4 batteries (3 for flight, 1 FPV gear/receiver), room at top for receiver and antennas.  When I began I wanted to build a pack with a small 3ft telescoping mast for the patch antenna.  Instead I choose simplicity, in the current design I mount the patch antenna directly to a plywood board within the pack and leave the front flap open when I fly.  I think there is a joke here but ah never mind.The BuildThe build is ridiculously simple and no frills.  First I cut a piece of plywood 8"x6"x1/4".  I purchased a piece of Poplar wood in a hobby store display box or the local hardware.  On this board you will mount the receiver and patch antenna.  Next, cut some holes in on the right side of the board for your patch antenna.  To get correct hole alignment and sizes I taped a piece of paper on the back of the patch antenna and rubbed the holes with a pencil.  Once you have the correct layout, tape the template on the board and drill holes as necessary.  Use self-adhesive velcro Command Strips to securely attach the patch antenna in addition to screwing the antenna to the board.  You will need M3 screws long enough to pass through the board and mount to the antenna.  Next, mount the receiver with the velcro straps. More to do...I need to change the FPV backpack power connector from XT-60 to HTX style.  The reason is that the FatShark goggles support a maximum of 3s battery pack.  All my flight batteries are 4s with XT-60 style connectors.  I know one of these days, when I'm tired, I will plug in a 4s battery and their will be a mushroom cloud in the my backpack.  To make sure I don't make that mistake, I will use HTX style connectors for the backpack power supply and XT-60 style connectors for my aircraft.  I also plan to sew loops on the front of my pack as velcro points to secure my aircraft.  I don't want to carry the aircraft if I'm hiking.  As a safety measure, I need to add a fuse or circuit breaker to the main backpack power supply, 2A-3A should be adequate.  The antennas range is probably attenuated due to proximity to the ground.  I will include future tests to see how this configuration compares to FatShark mounted antenna.  The pack includes an exterior pocket and strap for carrying a small tripod.  I was thinking it would be interesting to hang the pack using the top strap on a tripod to get the patch antenna off the ground.  The interesting testing scenarios I'm considering, open to suggestion, are 1) FatShark mounted antenna, 2) pack on ground, 3) pack suspended via strap on tripod.  I have also considered adding a 5" TFT display so others on the ground can see what I see as I fly.  It's a good way to share the experience with everyone on the ground.  If you add this to your pack you should quickly review the current draw to make sure the circuit breaker\fuse will accommodate the increased load.  I will update this article in the future but hopefully this is enough information to get everyone started.  Happy flying!

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