Interference w/ GPS

[danstah]

So we are using a 2.4 GHz video transmitter on our UAV's and have been getting a lot of interference with our ublox LEA-4P using an 18mm patch antenna on a ground plane. The problem is that the transmitter itself is leaking RF and interfering with the gps not the antenna (or at least i think so). Does anyone have any suggestions for how to stop this interference. Also does anyone know any high quality small transmitters for any frequency's that don't have as much signal leakage?


We have tried wrapping the transmitter in grounded aluminum foil with little to no success as well

Also does anyone know if you can buy a single transmitter that can broadcast on multiple channels simultaneously?

[clolson]

So we are using a 2.4 GHz video transmitter on our UAV's and have been getting a lot of interference with our ublox LEA-4P using an 18mm patch antenna on a ground plane. The problem is that the transmitter itself is leaking RF and interfering with the gps not the antenna (or at least i think so). Does anyone have any suggestions for how to stop this interference. Also does anyone know any high quality small transmitters for any frequency's that don't have as much signal leakage?


We have tried wrapping the transmitter in grounded aluminum foil with little to no success as well

Also does anyone know if you can buy a single transmitter that can broadcast on multiple channels simultaneously?

I'm no RF expert, but we have seen problems with both our 900 Mhz and 2.4 Ghz transmitters interfering with GPS reception. Not being an expert, our simple solution was to move the GPS antenna further away from the other transmitters. We've also had success with lowering the transmission power of the conflicting transmitters. At 100mw output I think I could directly wire the 900mhz or 2.4ghz transmitters to the gps receiver and not have a problem. At 1watt output, I have to move the gps antenna about as far away as the cord will reach (maybe almost a meter?)

Curt.

[dmgoedde]

I've been OK at 1 full Watt output from XTend 900 MHz modem, in the case of GPS receiver having built in SAW filter.

[matttay]

So we are using a 2.4 GHz video transmitter on our UAV's and have been getting a lot of interference with our ublox LEA-4P using an 18mm patch antenna on a ground plane. The problem is that the transmitter itself is leaking RF and interfering with the gps not the antenna (or at least i think so). Does anyone have any suggestions for how to stop this interference. Also does anyone know any high quality small transmitters for any frequency's that don't have as much signal leakage?


We have tried wrapping the transmitter in grounded aluminum foil with little to no success as well

Also does anyone know if you can buy a single transmitter that can broadcast on multiple channels simultaneously?

Note that wrappign the antenna in grounded foil means that it's grounded at DC...it could in fact be a poor ground that appears as an open at 2.4GHz. If you don't have a network analyzer, you won't know this for sure.

Find some copper tape, and competely encase the transmitter in that (except for ant + power), and then solder the seams. If that helps, then indeed it means your interferer was being radiated out of the transmitter. If it doesn't help, then it means your interferer is being conducted out of the remainig openings (wire for power and antenna) and in that case you've got a tough problem because the interferer (~1.5GHz) is so close to the TX freq (2.4 GHz). Filtering that will be hard.

All transmitters will "splatter" outside of their band. It's tough with GPS because if you are transmitting at 20 dBm (100 mW), then your noise as seen by the GPS needs to be knocked down about 170 dB from 2.4 GHz to 1.5 GHz. A digital transmitter will have much less splatter usually than an analog video transmitter because most digital modulation schemes have a fairly high linearity requirement. But much depends on the quality of the design too.

[DrDon]

Because you are using a passive patch antenna, you will be susceptible to antenna de-tuning/saturation by RF equipment near by. Locating your transmitting antenna FAR away from your GPS antenna and changing the orientation of the antenna can improve results. Also you may want to use an active/external antenna which are much less susceptible to impedence mismatching and RF interference.

Dr Don
http://www.iat-llc.com
Automation Sensors, Systems, and Services