Few questions about FM searching

 

There are very few FM searching machines. This problem should be divided into two categories,

Category 1: If you manually adjust each station, you can hear clear radio stations. You only need to change the stop threshold of the station

The number of search sites has increased,

Another type: manually adjust to a radio station with poor signal, and compare it with the FM of the brand mobile phone, it is found that the FM effect is obviously worse than that of the brand mobile phone, for example, the brand Mobile Phone is clear without noise, however, the FM performance of your machine is poor, and it is a murmur. This is because the FM is disturbed. You must modify the hardware parameters to solve this problem;

There are three ways for FM to be disturbed,

1. noise is introduced from the antenna input end;

2. noise is introduced from the power supply end;

3. noise is introduced from the ground;

4. Radiation interference;

Solution:

1. Identify whether the noise at the input end of the antenna is caused by disconnecting the line from the input end of the FM antenna to the earphone and directly welding a length

Headphones and other long thin lines when the antenna, if

At this time, the noise disappears, proving that the noise was introduced from the antenna. This problem is better solved, and the noise usually passes through

The Baseband Chip is introduced to the headset in terms of left-right channels, etc,

As long as a large magnetic bead is attached to the left-right channel, mic, and earphone detection line, such as a magnetic bead with a frequency of 100 Mbit/s impedance of 1.8 kb. of course, the larger the impedance of this magnetic beads, the better the noise blocking performance, the recommended frequency of 100 m impedance 2.5 k magnetic beads. this prevents the noise in the FM band from interfering with the headset antenna.

In addition, the plug-in end of the earphone prevents some of the ESD components from having a large parasitic capacitance, which may cause loss of the air signal induced by the FM antenna. You can also disconnect and try again.

2. The noise from power supply can be in the vicinity of the FM chip power supply, and the capacitance of 1nf, as well as a string of one in the FM power supply entry

A 100 m impedance 2.5 k magnetic beads can help filter out interference of about 100 m in the FM band;

3. The PCB must be re-painted for ground interference. For details, refer to the PCB layout guide: rda5800c.

PCB layout guide_v2.0.pdf.

4. Radiation interference,

To determine the radiation interference, you can find a mobile phone, such as a Nokia mobile phone, enter the FM, and find a station with a weak signal (it sounds like

When the mobile phone or mobile phone antenna is close to each part of the machine

When the disturbance is large, it can be found that this is a radiation interference source, the radiation interference source, generally can be shielded by a metal cover dry

Source to solve the problem;

Such as audio Class D power amplifier, switching power supply, DC-DC, DRAM control bus, RGB screen and so on are relatively large sources of interference;