Transmitter PS

[NZ0I]

The first Ver X2 Dual-Band Transmitter power supply has been assembled, and it seems to be working adequately. There was one wrong footprint, but the workaround was easy enough. Some discoveries will lead to circuit changes in the next board spin. The main thing that I discovered was that the switching supply in shutdown will still put out 4V (the LiIon battery voltage) - which will pose a problem. So I will add some circuitry (a FET) to cut off all output from the switching supply when it has been shut down. The other thing that will be addressed in the design rev is voltage drop between the LiIon battery and the switching supply. The voltage drop wasn't much of an issue in the receiver power supply, which draws only about 100 mA from the batteries. But the transmitter will likely draw up to 3 amps from the batteries (for brief periods) and only a few tenth's of an ohm can result in 0.5V drop, which is significant when the batteries only put out 3.2V to 4.2V to start with.

The switching supply puts out +12.8V with no load, and drops to +12.6V when providing 500 mA of current (6.3W). Switching noise on the DC output is about 1V p-p. When providing 255 mA to a 47-ohm resistor the efficiency measures ~76%. Not spectacular considering that the device claims it can provide over 90% efficiency, but 76% is not too shoddy. All components (except the load resistor) remain cool to the touch even when providing 500 mA at 12.6V. Efficiency might be improved with a higher-Q inductor, or lower on-resistance switching FET. But the performance as measured now should be adequate for powering the transmitter.

The LiIon charging circuit, which now supports using a wall wart, seems to be working just fine so far. 

Ver X2 build out is being documented here: http://openardf.org/index.php/ardf-open-equipment-project/documents/x2-buildout/

I'll add some pictures of the PS board once I'm done experimenting with it.

[NZ0I]

The Ver X2 Transmitter build out page has been updated with some pictures: http://openardf.org/index.php/ardf-open-equipment-project/documents/x2-buildout/