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Author Topic: Help with QN8027 FM chip  (Read 290 times)
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PM3295
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« on: May 20, 2020, 08:27:36 20:27 »

People,

Is there anyone who had some experience using this FM chip?
https://datasheetspdf.com/pdf-file/761694/Quintic/QN8027/1


I got the chip working, but the RF output is very low. The data sheet states 121 dBuV but no reference impedance. If I assume 50 Ohm, that means that you should get +14 dBm at the full-power  setting. The best I can get is about -14 dBm. There is a register value that determines the output level, but leaving it at default or writing the max level to it, the level never goes above -14 dBm. It is stated that leaving it at the default value should give maximum RF output power.

I have tried a few chips to make sure I am not dealing with a faulty chip, but they all produce a maximum of -14 dBm.

I watched a few YouTube videos of people using the chip and from what I could see from the one video, the person measured the output level on a SA and it looked like a level around the -15 dBm mark.

Can it be an error in the data sheet? I could not find any other/later version of the data sheet.

Thanks in advance.
« Last Edit: May 20, 2020, 08:47:12 20:47 by PM3295 » Logged
h0nk
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« Reply #1 on: May 20, 2020, 09:18:26 21:18 »

Hello,

if You want a cheap and not to weak FM-transmitter, you should
look for a Sony-Ericsson MMR70 module.
If You set the Register 2 with the value 0xC2 they produce around
2 V at the antenna pin. This is approx. 80 mW.
You can buy this modules on Ebay.
If You need further information about the modules, let me know.

Best Regards
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PM3295
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« Reply #2 on: May 21, 2020, 02:30:11 02:30 »

Thanks for the info. I may look at it at a later date. I got about 100pcs of the QN8027 from a friend and would like to implement it in a small (post stamp size) module. According to the data sheet, this chip can also transmit RDS data.
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bigtoy
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« Reply #3 on: Today at 02:17:42 AM »

Definitely not 121 dBuV into 50 ohms. The datasheet states, in "note 3", that output voltage is presented to a matched antenna (which will have a much higher impedance), and refers you to an application note. I believe this is the application note:

https://cdn.hackaday.io/files/4149177510816/QN8027_SANB_Hardware_Application_Note_V_0_25_102209.pdf

The application note doesn't help too much. Without either the datasheet or app note describing the output impedance of the RF power amp, how are you supposed to calculate power, match to it, etc? I suspect that the -14 dBm you're getting is the truth.
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vern
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« Reply #4 on: Today at 10:14:44 AM »

Quote
Definitely not 121 dBuV into 50 ohms
I disagree, if it can deliver 121 dBuV into a 50 Ohm antenna, it will deliver the same power into a 50 Ohm load if that load is suitable for the frequency.

Quote
that output voltage is presented to a matched antenna (which will have a much higher impedance)
50 Ohms is 50 Ohms
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