In my latest project (more data-logging stuff), I’m using an LS20031 GPS module alongside a ConnectOne NanoSocket WiFi module, and when I say alongside, I mean, alongside, like practically right next to each other, about two inches between the GPS module and the WiFi SMT antenna.
I initially thought the GPS module was dead…well, wasn’t so.
While playing with the project, I semi-accidentally unplugged the WiFi module, and amazingly enough, the GPS module started working, and of course I spent X hours searching for why the WiFi module quit working
So, a quick bit of searching and I figure out that the GPS L2 signal is 1227.60 Mhz, which if doubled, 2445.2Mhz, falls inside the WiFi 802.11b/g frequency range, not exactly on any one channel frequency, but close enough to where I think I’m wiping out the incoming GPS signals with the outgoing WiFi signals with a bit of harmonic action going on here.
I’ve got the GPS module and WiFi module power sources sufficiently decoupled, running the whole thing off a decent sized LiPo batt pack with good wiring/regulators/etc, a generous sprinkling of .1uf cap’s all over the place, along with a 47uF bulk storage cap at the WiFi module.
I’m guessing that no amount of decoupling is going to fix this issue, and that the only fix here is going to be to just plain increase the distance between the two modules.
I am not an RF engineer, but I did stay at a Holiday Express once…
Self jamming is a distint problem. But it may not be from the radio waves from the antenna but rather the local oscillators on the two units. My experience with other systems has shown that a GPS unit can be sensitive to EMI at multiple bands other than the L1/L2 frequencies. Consider an RF shield (Faraday cage) around both the WIFI and GPS units. This may greatly lower the jamming you are experiencing.
fll-freak:
Consider an RF shield (Faraday cage) around both the WIFI and GPS units. This may greatly lower the jamming you are experiencing.
Wwwwwwwhhhhhhaaaaaa???????? :shock:
Might also remove the chance of receiving ANY GPS signals and/or transmitting or receiving ANY WiFi signals too! :lol:
Not really. I smell what your cooking. And I get what your saying about the L/O’s on either module. Just at first thought, I smelt something fishy when I found L2 * 2 = WiFi-ish frequencies.
I guess I should have mentioned that the only thing penetrating the cages should be the antennas! Just to be clear, I am suggesting a cage for each of the two units. Copper foil is often your friend in these cases.
First of all, no GPS module sold by sparkfun uses the L2 frequency. They’re all L1 only, at 1575.42 MHz.
Nontheless, there can be jamming/interference problems between two frequencies, without necessarily one frequency being a multiple or submultiple of the other. For possible solutions, I’d try
filtering the GPS using a SAW right after the antenna, possibly followed by a LNA and perhaps another SAW
Physical distance between the two antennas (as you already suggested)
time-multiplexing the use of Wi-Fi and GPS. If you can get a (hot-start) GPS fix in a few seconds, just shut down the Wi-Fi chipset during that time. In many application scenarios this can be worked out.
First of all, no GPS module sold by sparkfun uses the L2 frequency. They’re all L1 only, at 1575.42 MHz.
DOH! I knew that! Somedays...I tell ya...
Nontheless, there can be jamming/interference problems between two frequencies, without necessarily one frequency being a multiple or submultiple of the other. For possible solutions, I’d try
filtering the GPS using a SAW right after the antenna, possibly followed by a LNA and perhaps another SAW
Physical distance between the two antennas (as you already suggested)
time-multiplexing the use of Wi-Fi and GPS. If you can get a (hot-start) GPS fix in a few seconds, just shut down the Wi-Fi chipset during that time. In many application scenarios this can be worked out.
E
Both the GPS and WiFi modules are using built-in antennas. Ain't no breaking out nothing for nuttin' :)
Tried the time-multiplexing. Not digging the amount of time it takes the WiFi to re-lock. The GPS usually hits within about 5-10 seconds, but the WiFi takes significantly longer, upwards of 30 seconds depending.
Think I’ll just go with the distance fix for the issue.
I guess I should have mentioned that the only thing penetrating the cages should be the antennas! Just to be clear, I am suggesting a cage for each of the two units. Copper foil is often your friend in these cases.
:) It's all good.
But besides that, as mentioned above, the antennas on both modules are integrated on the PCB.
I’ll just stick with whatever distance I find that keeps the two from bugging each other.
I’d get a meter or so of separation between WiFi and GPS.
And ensure the Vcc/power is well decoupled.
A WiFi client device should not transmit anything unless it is hearing beacons from an access point (WiFi router). If configured in 802.11 Ad-hoc mode, the client may transmit its own beacons.
Shouldn’t be a difficult issue. Also, look at the specific WiFi frequency (channel 1, 6 or 11 are the most prudent WiFi channels in 2.4GHz).
GPS receivers work with incredibly weak signals and thus are prone to interference. But gee, smart phones (like my Android HTC) have GPS and WiFi and Bluetooth (also 2.4GHz) and GPS works fine. The antennas are inches apart.
Don’t overlook the obvious too, such as the WiFi or GPS device is causing the Vcc current consumption to increase to a point where the regulator ceases to work properly. Symptom of removing one device could give false symptoms!
I’m out in the sticks, so WiFi interference from the guy next door isn’t a problem. I’ve tried the oddball channels for the heck of it. No dice. Tried a little ‘experiment’ in the basement earlier tonight. Almost impossible to get a decent GPS lock so it’s a bit of a ‘worst case’ as far as the GPS goes.
~1ft got me barely a GPS lock, 2ft worked good enough, 3ft was almost perfect. I’ll stick with that.
