DCT is "Digital Command Transponder" which makes about as much sense as IHU, but it's the Gofl name for the chip. That command can set two levels, I think, and each pair can be set for either safe mode or non-safe. In other words, you can set it so if golf is in safe mode, it will be either high or low, and also if it not in safe mode, it will be high or low. I don't remember what I did with the command on Pacsat. But look where in MRAM that command puts a value, and then search for the MRAM name in other places, and you can probably see what it does to change the power.
73,
Burns Fisher, WB1FJ *AMSAT(R) Engineering -- Flight Software*
On Mon, May 13, 2024 at 11:58 AM Bob Stricklin via pacsat-dev < pacsat-dev@amsat.org> wrote:
We have a functioning PA. The final level is low at this point but that should be a matter of running things.
The input drive level is also very low. Is there a provision in the code to turn adjust the drive level? I see a command "Set dct drive power” but what is dct? I hope it the name of the AX5043 register. Also see “SELECT DCT POWER”. What does this do?
I hope one of your knows the combination otherwise I can start looking at the data sheet and manual for AX5043?
The magic here has to do with the Vbias level on the LDMOS. I just copied the example in the data sheet and they never talk about what the Vbias level should be. The level also sets up the quiescent current in the LDMOS and critically biases the device. I took out the filtering and matching and just capacitively coupled the input and output then tuned the Vbias. The operate point is going to be about 2.9 volts to 3.4 Volts. at 2.8 volts the Ids through the device is 100 ma and it goes up fast from there. We will need a Ids of about 300 to get 2W operation.
WE need to be thinking about turning on and off the supply voltage to the PA when we transmit. This will save a lot of battery power and a heat reduction.
Currently when I turn the Vbias up to about 2.9 volts I get extra oscillation. This should be eliminated by adding matching components back in. I have included two images of the signals with and without the oscillation. The level of output is about -40dBm with the current setup and it is sending packets to the ground station fine.
Photo of my setup for spectrum analyzer testing included. Using a stack of attenuators on transmitter. The Rx antenna is two of the clip leads together and clipped on Rx antenna.
One thing to look for at Hamvention would be a low cost rubber ducky antenna for 2M and 70cm. Either dual band or two singles. If we want to keep spending money on this we could probably use 8 of these antennas.
Bob N5BRG
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