Actions
Forum Thread Details
  • State Verified Answer
  • Replies 5 replies
  • Subscribers 93 subscribers
  • Views 397 views
  • Users 0 members are here
Related

FM transmitter noise

spekis

 Hi. I'm an hobby diy enthusiast. I was trying to find a simple and stable FM transmitter circuit. Found one with MAX2606 voltage control oscilator.

image

 At first the circuit workd well so I went to the next step and connected the input signal from COOLAUDIO V2902 digital audio processor. And then everything got complicated.

image

 The signal started to distort and pop once I enabled the digital output. However the noise becomes quiter when i touch the signal components.

 So my question. Is this an shielding issue? Should i put the transmitter board in a metal box?

 Thank you in advance! 

Parents
  • +1

    Other than shielding or grounding issues I would check signal levels. Distorted sound and "pop" also happen when the signal is constantly saturating the input of your transmitter.
    First, I'd use the analog outputs of the IC not the digital. I Googled the transmitter circuit that you are using and it looks to me like it expects an AC signal. The analog output voltage levels of this V2902 seem to have a 0.5V DC voltage, that you should get rid of with dc-blocking caps (as the picture shows).
    It would also be wise to add an op-amp or buffer between your audio IC and your transmitter.

    I'm definitely not an expert though, but that's what I'd check in that situation.

Reply
  • +1

    Other than shielding or grounding issues I would check signal levels. Distorted sound and "pop" also happen when the signal is constantly saturating the input of your transmitter.
    First, I'd use the analog outputs of the IC not the digital. I Googled the transmitter circuit that you are using and it looks to me like it expects an AC signal. The analog output voltage levels of this V2902 seem to have a 0.5V DC voltage, that you should get rid of with dc-blocking caps (as the picture shows).
    It would also be wise to add an op-amp or buffer between your audio IC and your transmitter.

    I'm definitely not an expert though, but that's what I'd check in that situation.

Children