Receiving LRO and LCROSS

This page documents my attempts to receive the S-band downlink of LRO and LCROSS using mostly what I already have in stock. This includes using the USRP and GNU Radio as software receiver. It is important to note that we are only talking about detecting the presence of the signal from the spacecraft and not decoding the signal. Decoding would require a much higher G/T than what can be achieved with small antennas.

Link Budget
To be written.

Notes:
 * For the S-band, LRO has omni (assumed 0 dBi) and a HGA (assumed 20 dBi) Gain assumption for HGA might be optimistic?
 * LRO transmission modes for S-band downlink: 3M40G2D, 4M57G2D, 5M00G1D.
 * LRO transmission modes for Ka-band downlink on 25.650 GHz: 57M25G1D, 114M50G1D, 229M00G1D.
 * LRO downlink data volume is 461 Gb per day @ 100 Mbps
 * LCROSS transmission modes for S-band downlink: 3M41G2D, 5M00G1D
 * LCROSS Telemetry: Spacecraft communications are provided through two medium gain antennas operating at 1.5 Mbps (nominal), two omnidirectional antennas operating at 40 Kbps (nominal), and a 7-watt S-band radio frequency transponder.
 * SNR @ 1 MHz is for USRP+DBSRX, which has a programmable channel filter that can be as narrow as 1 MHz.
 * SNR @ 100 Hz would be for a standard ham radio receiver in narrow CW mode.

Components
To be written.

Antenna

 * Dish
 * Feed
 * Mast and mount kit

Low Noise Amplifier
Kuhne KU LNA 222 AH HEMT super low noise amplifier is mounted close to the antenna feed and is used to improve the receiver performance by increasing the figure of merit (G/T).

Expected performance gain TBD.



Bias-T
Kuhne KU BT 271 N 10–3000 MHz bias-T is used to inject DC supply voltage needed by the LNA into the coax cable (thereby save a DC cable from shack to antenna).



RF Front-end (tuner)
This component is the RF daughter-board that plugs onto the USRP. It converts the high frequency RF signal to I/Q baseband that is is passed to the USRP ADCs. The options for this include the RFX2400 and DBSRX.

RFX2400
Initially, this option was considered; however, since the RFX only covers 2.3 to 2.9 GHz it is not suitable for this experiment. Even if it was possible to go down to 2.25 GHz, the noise figure of this receiver is worse than the DBSRX.

DBSRX
The DBSRX is a 800 MHz to 2.4 GHz receiver with a 3-5 dB noise figure and a software controllable channel filter that can be programmed between 1 MHz and 60 MHz.

It contains an MGA82563 wide band LNA followed by a MAX2118 DBS direct conversion tuner chip, followed by an AD818x (TBC) VGA. Note that according to the MAX2118 data sheet, the tuner is specified to work in the 850-2175 MHz range.
 * DBSRX block diagram (incl gains, AGC, dyn range)
 * DBSRX schematics
 * DBSRX PCB
 * MGA82563 data sheet
 * MAX2118 data sheet
 * AD818x data sheet

Software Receiver
The software receiver is implemented using GNU Radio. Since we only want to detect the signal (but not decode), the signal processing can be very sinmple and consist of some basic filtering, down-sampling and display of the baseband data coming from the USRP.

Wiring
To be written.

System Tests
To be written.

OTA Results
To be written.