Quick Answer
Your GPS module cannot find satellites because of where you mounted it, not which module you bought. The VTX, ESC noise, and carbon fibre shielding all jam the weak GPS signal. A mast mount that lifts the antenna 30mm above the frame, with the patch facing skyward, fixes most acquisition problems.
Why Your GPS Cannot See Satellites
We see this in the workshop every week. A customer brings in a build with a HolyBro M10 GPS module strapped flat to the top plate, sitting above the VTX antenna. The GPS finds two satellites and gives up. The fix is placement, not a better module.
GPS signals arrive at roughly -130dBm, below the noise floor of most RF environments. Your VTX at 5.8GHz pumps out up to 1W. Even harmonics far from 1575.42MHz L1 are strong enough to desensitise the GPS front end within 20mm. ESC switching noise adds interference in the 1-2GHz range. Carbon fibre blocks and detunes the antenna. You have built a GPS jammer.
Three Placement Rules We Follow on Every GPS Build
1. Get the antenna above the frame. We use an anti-interference GPS mast mount on every 5-inch build. The mast lifts the ceramic patch at least 30mm above the top plate, clear of the carbon shield and VTX radiation. On micro builds, we use a small foam standoff on the canopy.
2. Face the patch skyward. GPS patch antennas are directional. The ceramic element receives best from directly above. Mounting it sideways cuts received signal by 15-20dB. That is the difference between twelve satellites and zero.
3. Route the cable away from power leads. The Flywoo JST-SH GPS cable carries UART data and 5V. Route it along the frame edge, away from ESC motor wires. We once traced a GPS dropout to a cable running parallel to XT60 leads for 40mm. Moving it added six satellites.
The Three GPS Killers on an FPV Quad
The VTX is the worst offender. Even though 5.8GHz is far from L1 at 1575MHz, the power amplifier generates broadband noise extending below its fundamental frequency. A VTX running 800mW can desense a GPS receiver from 50mm away.
ESC switching noise is the second culprit. BLHeli_32 and Bluejay ESCs generate RF hash across a wide spectrum including L1. The mast mount solves this by getting the antenna physically above the noise source.
Carbon fibre is conductive. A GPS patch on a carbon top plate has its sky view blocked below, and the conductive surface detunes the antenna. The mast mount lifts the element into free space.
Checking GPS Lock in Betaflight
We consider eight satellites the minimum for a reliable 3D fix. If the count jumps between three and eight, you have an interference problem that will cause GPS Rescue to fail. Watch HDOP too: below 2.0 is usable, below 1.5 is good. HDOP above 4.0 with eight satellites means marginal signal quality.
FAQ
Q: Does a more expensive GPS module solve interference?
A: No. The M10 chip in the HolyBro is one of the most sensitive consumer receivers available. Mount it poorly and it performs worse than a cheap M6 on a proper mast. Buy the mast first.
Q: Can I mount the GPS on the bottom of the frame?
A: Not recommended. The bottom plate has the battery, PDB, and ESC wiring radiating noise upward. The sky view is also blocked by props. Top-mount on a mast is always better.
Q: How far from the VTX should the GPS be?
A: As far as possible, at least 40mm vertically separated. On 5-inch builds, we put the GPS mast at the rear and the VTX antenna at the front for 80-100mm separation. See our antenna placement guide for layout diagrams.
Q: Why does my GPS take five minutes on cold start?
A: Cold start means the receiver must download the almanac at 50 bits per second. With a well-placed antenna, expect two to three minutes. Longer than five means placement is the problem. See our GPS modules guide for module-specific tips.
Q: Will GPS Rescue work with only six satellites?
A: It will attempt it, but position accuracy will be poor. We set the minimum to eight satellites. See the GPS Rescue setup guide for configuration. Browse our GPS modules collection for hardware options.