I got a pixhawk 2.4.8 and 3dr 1000mw telmetry. the problem with the telemetry is that i can only set sik radio power up to 20(100 mw) under initial setup. how to set power to 1000 mw for my telemetry radio?
Set it for 20 and the radio will produce full power. Those radios have a fixed final gain stage amplifier. So theoretically your radio would have an amplifier with a gain of 5. But no doubt you have one of the cheap Chinese radios claiming 1W output. Those radios are of such poor quality the noise produced can be problematic. Also, it’s doubtful it actually produces 1W.
This was discussed at some length recently:
It’s likely a HM-TRP module and the frequency and power output is hard-coded into the firmware image in it. They are not adjustable anyway.
Ah right. It’s the Si4432 that are adjustable.
Thank you for the reply. I am relatively new in this field. Didn’t know about the quality of the module . Will keep it in mind in future. Many many thanks.
Well, a power amplifier circuit is non-adjustable in the first place. It has a certain amount of gain built into the circuit. What makes it adjustable is the amount of drive to the circuit, which is the power input to the amplifier.
The reason these are non-adjustable is because the firmware image is hard-coded for a specific output from the driver. The module can be reflashed with firmware that will allow adjusting the driver. But the unit will likely not work if you cut the drive level to the final amplifier stage.
It is unlikely the amplifier has a gain of 10dB to get 30dBm output with a 20dBm drive. The radio would be unusable. It is usually more like 3dB gain so the PA stage actually puts out 200mW. They advertise these radios with anywhere from 200 to 1000 mW output but that is mostly advertising, depending on how much the seller wants it to put out on paper for advertising purposes. You would not be able to power it from a USB port if it was actually putting out 1000mW. With an internal circuit power efficiency of 50% the the amplifier would pull 0.4 amps alone.
gain is in dB. So assuming the drive is 20 dBm (100mW) a gain of 5 db in the amplifier would give 25 dBm output, or 316 mW. Doubling the power increases gain by 3dB.
It is hard to know exactly what these radios put out without putting them on the scope.
Edit: a decent high-quality amplifier can do 10dB no problem, and get 5x the drive power. But a high-quality amplifier is something these radios do not have
I meant 5X but you are right about the proper units for gain. Thanks for the detailed info Chris!
The thing is, I’ve seen some of these radios that work decent. Others are unusable because they cause too much onboard interference from spurious emissions due to over-driving the amplifier.
If you have a set that works and doesn’t seem to cause any interference, run them. They won’t cause a problem. If you have fix one that is problematic, then you have to jump thru hoops to reflash it to cut the power from the driver until it cleans up on the scope. Which requires an intimate knowledge of AT commands to do so, since there is no “point and click” interface to configure one.