Synaps3
Member level 1
I have built an FM transmitter circuit using the RDA5820. (It is one of those all in one FM stereo transmitter chips).
Anyway, it has a problem with what I think is the PLL unlocking after a few minutes of transmitting. It makes a loud popping noise and the carrier is shifting on the analyzer. I am pretty sure there is nothing wrong with my circuit. The only thing I am unsure of is the antenna matching. Right now the antenna output goes through 100p and into an op-amp.
I found that the problem is fixed by placing a small piece of metal on top of the chip. However, it only works once the problem has started. If I leave the metal on there before the problem, it doesn't fix it :bang: I know it seems like some type of interference, but I tried shielding everything and nothing changes.
I really don't know much about RF yet, so could you please give me some ideas of what to try? It's also possible that the module I am using is defective (I am not using the chip directly).
Here is what I am talking about:
Anyway, it has a problem with what I think is the PLL unlocking after a few minutes of transmitting. It makes a loud popping noise and the carrier is shifting on the analyzer. I am pretty sure there is nothing wrong with my circuit. The only thing I am unsure of is the antenna matching. Right now the antenna output goes through 100p and into an op-amp.
I found that the problem is fixed by placing a small piece of metal on top of the chip. However, it only works once the problem has started. If I leave the metal on there before the problem, it doesn't fix it :bang: I know it seems like some type of interference, but I tried shielding everything and nothing changes.
I really don't know much about RF yet, so could you please give me some ideas of what to try? It's also possible that the module I am using is defective (I am not using the chip directly).
Here is what I am talking about:
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