Predicting ground station performance during testing

Added by J. Simmons almost 7 years ago

We are about to begin formal testing of prototype 1. In preparation for this testing we need to finish documenting our test procedures and conduct any required analysis to support those tests. For prototype 1, the key tests are covered in the Test 1.1.2 Instructions. These tests include a lab test to confirm the completed ground station can receive signals at 915 MHz as expected, a field test to simulate from orbit communications using long distance signals on Earth plus attenuation, and a from orbit test (if possible). The first two tests require analysis to predict the performance and/or determine test conditions (for example how much attenuation is required during the field test). Note, the Preliminary Design documentation should include all required values for the ground station and CubeSat radios/antennas.

Wilton has volunteered to provide some of this analysis. In particular, he is working on determining the predicted performance of the ground station during the lab test so we can compare the actual performance and determine is the system is working as designed. Below are his comments (and attached is his updated link budget).

I added some new columns to the Link Budget for calculating power setting for the test transmitter to test/simulate similar signals on the ground station.

I assumed that the test transmitter would be an omni-directional antenna, but the power needed to transmit is pretty small so perhaps using a directional antenna but not aiming it directly at the ground station may make a better test signal. I know the transmitter can go down to -30dBm but I don't think the side channels are supressed as well so operating the transmitter in the lowest power setting has the worst/noisiest setting as well so it won't be the cleanest signal.

I attached the spreadsheet to this email.

Will

Wilton or Aaron, can either of you walk me through these calculations to help me understand how we go from the attached link budget to an expected value in SeeDeR during the lab test? Also, is it possible to adjust the transmit power on the test radio and confirm we get predicted signal values for say 3 signal strengths?


Replies (1)

RE: Predicting ground station performance during testing - Added by Wilton Burke almost 7 years ago

Couple things on the spreadsheet. Looking back over it the M is meters. I should have used a m. And the power is actually in Watts not mWatts.

The test radio should be set as close as possible to the power listed in the last 2 columns. For the in lab testing ( 1 meter) the min power setting should be close and at 100 meters it should be set at ~10mW.

For 1 meter
The minimum power of 0.001mW should be used but because of near field effects, side channel noise, multipath etc you may have significantly different results so getting an accurate in lab test beyond works/doesn't work will be challenging. If there is a direction antenna available we could use it to hopefully reduce the other noise effects. In that case we could map out the transmitting antennas gain and boost the transmitter up some and not aim the antennas directly at each other

For 100 meters
Theta Test Tx Power
79 0.356mW
45 4.89mW
0 9.78mW

(1-1/1)