Mavic Mini (A Look Inside)
- Thread starter Drone Master
- Start date
I found the full datasheet with application circuit diagram and evaluation board of the SKY 85748-11 5GHz front end IC:
Based on Blithe74’s photos, it seems, there are three paths from the Atheros WIFI controller to the antennas:
1: 2.4 GHz at CE power level (using the Atheros internal RF power amplifier?)
2: 5.8 GHz at CE power level (using the Atheros internal RF power amplifier?)
3: 5.8 GHz at FCC power level (using Skyworks 5GHz front-end/power-amp)
In the CE version, path 1 and 2 are equipped on the PCB. In the FCC version, only the path 3 components are soldered in.
1: 2.4 GHz at CE power level (using the Atheros internal RF power amplifier?)
2: 5.8 GHz at CE power level (using the Atheros internal RF power amplifier?)
3: 5.8 GHz at FCC power level (using Skyworks 5GHz front-end/power-amp)
In the CE version, path 1 and 2 are equipped on the PCB. In the FCC version, only the path 3 components are soldered in.
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I would be interesting to measure the integrated logarithmic power detector output level of the SKY 85748-11 (Pin5) in a MM FCC version while operating in USA and compare it to the output level of a MM FCC version while operating in Europe or another CE-country.
In CE-countries, it should be lower because even in the FCC version the output power is reduced based on the MM‘s GPS location.
In CE-countries, it should be lower because even in the FCC version the output power is reduced based on the MM‘s GPS location.
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The datasheet is very easy to find.... do we know if I guessed the part number correctly?
Blithe74
Active Member
Is this main question 748 or 746?
Can You make some better photo the chip SKY74??? and answer to us it SKY8574?
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Blithe74
Active Member
I think You a right. One photo of CE version:
If the Chip 213GAA is SkyWorks AS213-92LF, it is not amplifier, but Tx/Rx switch, and CE version not have amplifier for one of two frequence range...
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I think, the middle path is the 5.8GHz-CE version - as you suggested without power amp.
Thus I believe, the left path is the 2.4GHz CE subcircuit.
It would be interesting to know, what the black 8-pin IC in the upper left corner of the photo is. May be a 2.4G power amp including switch or a RX/TX-swith only.
Based on this video
It looks like the FCC version just disables the 5.8Ghz amplifier on the SKY chip if it sees GPS coordinates outside of EU.
If someone can check the logical level of pin 6 on a FCC version first in US and then fakeGPS to EU. If it changes from 1 to 0 then a simple permanent hardware fix would be to jumper pin 6 to 3.3V VCC somewhere on the board. This will permanently force full power on the SKY chip. Someone more experienced in electronics to correct me if I'm wrong.
If someone can check the logical level of pin 6 on a FCC version first in US and then fakeGPS to EU. If it changes from 1 to 0 then a simple permanent hardware fix would be to jumper pin 6 to 3.3V VCC somewhere on the board. This will permanently force full power on the SKY chip. Someone more experienced in electronics to correct me if I'm wrong.
Reading further the datasheet I might be wrong, because the chip utilizes 4 states, in 3 of which the PA_EN pin should be off. Which means it's constantly switching between TX and RX and only in TX state the PA-EN should be enabled. Maybe in EU even in TX state the PA_EN is still low and thus giving the lower output power....
Blithe74
Active Member
Yes, small change in hardware can resolved low output signal.
I think the transmitter level may be adjust by pin 5 (VDET) = 1V - full power.
I am following with great interest this hot topic. Big thanks to all tinkerers who do the research.
EDIT: When reading the datasheet it looks like VDET is an output, not an input?
It would not be a good idea to control RF power output via analog voltage input, as you'll have to somehow control the voltage on the MCU output pin, PWM is not an option here...
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Blithe74
Active Member
I 've been thinking a lot about this conclusion. I couldn 't understand why I needed a Pin that showed the output transmit level, if I set the output level myself. After looking at the documentation for other amplifiers, I came to the conclusion that this output is used to set the output power. But I might be wrong. If there is a person with knowledge of this matter, please help us.
Your question is valid, but think of this. Since you can't actually measure how much power you're outputting (to meet regulations) in order to be 100% sure you need a real feedback on the output. And this probably is the VDET pin which gives you accurate measurement of how much power you're actually outputting.
Blithe74
Active Member
Do you think the Pin VDET is feedback? In this case, the amplifier has a strictly set gain factor, for example 10 times, and the output power depends on the level of the input signal. In My opinion, difficult, but I may be wrong.
I thought the input signal level should be the same, but the output power should be set on the pin at amplifier, but I may be wrong.
Yes, I think the amplification is fixed, it's just being turned on or off. Let's see if anyone else has an opinion on this.
Blithe74
Active Member
You are right. VDET is output Pin, for feedback (I very bad know English). In this time to deceive AR1021X we can decreased signal from VDET. But question, what will be with signal in FCC mode?
Blithe74
Active Member
Need documentation for AR1021X-CL3D for understand, how made output power control.
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