I have observed many many times during conventional menthod of current calibration of the 3DR Power module using arming the copter and motors that the current displayed by the power anlyzer is not stable and fluctuating by 1-2Amps or even higher. And calibration done via this old conventional is not proper and current reported in mission planner while the copter is in air, is in error by 1-2amps and that makes lot of error.

Initially I thaught of using two 100Watt 1Ohm resistors in parallel and energizing them via 30Amp brushed motor ESC connected to the output of the 3DR Power module (power tapped from same points where 4 ESC's are soldered. To control the brushed 30Amp ESC, I used standalone cheap servo tester. I mounted the two 100W 1Ohm wirewound resistors which were already in aluminium heat sinkable cases, on an additional large aluminium heat sink with a fan. I set the servotester knob to display 10Amps of current in the Turnigy Power Analyzer, but very soon the current dropped around an ampere lower. I again adjusted for 10 Amps and same thing again observed. Reason for this was the ohmic value of the resistor depend on the temperature and on increasing temperature the net resistance was increasing and hence the current drawn was decreasing. I then rejected this method and thought something else.

I then thought of using car head light halogen 100W lamp in place of two wirewound resistors, this was rather simpler and required no heat sink and the current drawn value whatever I set to was almost very stable. Rest you can watch the video. 

https://www.youtube.com/watch?v=vWPxR1D9vOo

I have a great news for the RC community that you can DIY the most powerful RC + Telemetry system on the market "ULRS 2000mW" using OrangeRX 433MHz 1W module and my 2W power mode. You need to have a magnifying lens and a small tip knife to do this mod. My greatest gratitude to FlipFlap (Ben) for his excellent firmware of ULRS.

Gain of the power MOSFET may differ slightly from module to module so one can get variation of 100 to 150mW higher or lower. Did the 2W mod in OrangeRX 433MHz 1W module and got 2030mW at 9V Drain supply.

I have cut a track on the RFM23BP which connects the RF MOSFET to the 3.3V main power line and power the RF MOSFET with external variable power supply and set it at 9V, achieved 2030mW RF output power. 

After running throught the night, measured the temperature of the RF power MOSFET, is was 148 deg F, on touching it was just warm, not hot. Its because of the fact that the PCB design of the RFM23BP and its integration in the OrangeRX host board all together makes a large heat sink for the RF power MOSFET.

Tested with inbuilt spectrum analyzer of ULSRcc, did not observe any unexpected surprise. Perhaps you can analyze that better with your real spectrum analyzer.

XBee Pro 50mW RPSMA - Series 2 (ZigBee Mesh) - Sparkfun part: sku: WRL-10419, can not be used for Two-Way telemetry.

If you are looking for two way telemetry using a pair of this module “XBee XBP24BZ7”, then better do not buy it at all, I purchased one pair and suggesting, based on my findings.

For transparent serial communication between the airplane and the ground station, you need to configure one of the mudule as XBEE COORDINATOR AT" and the other one as “XBEE ROUTER AT”.

The the X-Bee configured as “COORDINATOR AT” will be at the ground station and the other one which is configured as “ROUTER AT” will be in the airplane.
My findings are;

1. The speed of data flow from Rouert AT X-Bee to Coordinator AT X-Bee is very fast and have no issue.

2. The speed of data flow from the Coordinator AT X-Bee to Router AT X-Bee is very very slow and not acceptable.

When I tried to use with APM, It was very very difficult to read and write waypoints from the ground station.
First I suspected if there could be any hardware issue in one of the X-Bee but it was clear when the problem got shifted when I swapped the configuration of the two X-Bees “XBee XBP24BZ7”

I tried on different bauds and even newer and older firmwares of this X-Bee “XBee XBP24BZ7” but same problem.

However there is no such issue in “XBee Pro 60mW Wire Antenna – Series 1 (802.15.4)” sparkfun.com/products/8742

Digi needs to take care of this issue promptly if they really want to keep this product selling.

Recorded video, describing this problem:
vimeo.com/41900865