Hi
Can anyone give me any good ideas what might cause spurious responses?
I have a product we are making that has a microcontroller with wifi receiver/transmitter. The problem is that sometimes the spurious response is too high.
I have found that in some cases, it is caused by a bad soldering of a LCD screen (the screen works ok) on the product. How could that cause too high spurious response?
But there are other reasons, sometimes heating the microcontroller with adding flux helps. Can bad solders effect it that much (even if they are not in the rx/tx path)?
Also, I haven't found any useful information about spurious responses. Caould anyone suggest some resources?

 

any non linear connections in the rf field can cause mixing of signals and / or harmonics. corrosion, dissimilar metals, and such. even certain metals, such as nickle can cause spurious signals.

 

Is the spurious signal only on one board or a chronic problem? Where is the spurious signal compared to your desired signal, above it, below it or all over? In the WiFi passband or outside it? How does it compare in amplitude.

First you need to find the source of the spurious signal. One way to do that is to use a spectrum analyzer with a short wire on the probe. Sniff around the circuit to find where the spurious signal is strongest. It may be the oscillator or amplifier circuits.

Often it's due to impedance mismatches. A poorly soldered LCD screen could change the impedance enough to cause spurious signals. Besides having good solder joints you may consider isolating each part of the circuit from the others with a copper fence. You also may want to look at your ground plane and make sure you don't have any ground loops. I have even seen copper foil soldered over the tops of ICs to prevent them from oscillating. Another solution is to cover everything with RF absorbing foam.