Precise noise measurement in RF circuits is a technique, which Callisto has mastered by necessity through our work on ultra low noise amplifiers and receivers. Callisto has developed noise measurement equipment for ESA for use in satellite ground systems. 
Typical applications include monitoring reception system noise temperature, antenna G/T measurement and antenna calibration. Following are descriptions of two different types of noise measurement equipment, which Callisto has developed.
NTMS
The NTMS (Noise Temperature Measurement System) has been developed by Callisto for ESA for use in Ground Stations. It uses a novel method of measuring noise by using a digital test signal injected into the reception system. The noise level in the system produces bit errors when the test signal is recovered and demodulated. Using careful control of the test signal and complex processing, the noise temperature in the system can be derived from the bit error rate. The NTMS can be used for continuous measurement of Tsys, even when the station is tracking operational missions because it uses a spread spectrum signal.
NTMS – Details
A modulated test signal is generated by a test modem. The modulation is BPSK overlaid with a direct sequence spread spectrum code. This test signal is up-connected to RF and is coupled into the ground station receive chain at the input to the LNA. The test signal, together with the receive chain system noise and any operational signals received by the antenna, will then be amplified and down converted by the ground station receive chain (shown in blue in the diagram). At the output of the down converter, the test signal is recovered and demodulated.
The measurement configuration is shown in the diagram representing a ground station “front-end.”The transmitted data is compared with the recovered test data and errors counted. The Bit Error Rate (BER) measurements are processed in a PC and used to evaluate the noise temperature. As the test signal is spread spectrum modulated there is a low level of mutual interference between the test signal and any operational signals present in the downlink spectrum. Calibration of the measurement to a reference noise standard (noise diode) is built into the measurement system.
NTMS – Specifications
| Parameter | Specification |
| Measurement Resolution (DTs/Ts) | 1% |
| Measurement Accuracy | < 5% (RSS) |
| Degradation on telemetry/ranging channels. | < 0.1dB |
| Range of system noise temperatures | 20K to 300K |
| Measurement Bands | 2200 to 2300 MHz 8400 to 8500 MHz |
| RF Measurement Bandwidth | 100 MHz in slices of 24 MHz |
NTMS – Implementation
Click the photo for a detailed version.The NTMS comprises a modem unit, an up converter, calibration units and a PC running the process software. The figure to the right shows the graphic User interface. All NTMS equipment is designed for 19” rack mount, with the exception of the calibration units which are small RF modules designed to be installed in the antenna feed area.
RADIOMETERS
The radiometer methods use traditional detectors and integrators for measuring noise. The Radiometer system developed by Callisto has two modes of operation:
1. Total Power Mode (TPR)
2. Noise Adding Mode (NAR)
The TPR mode is used when the highest level of sensitivity is required. However, the TPR is not automatically re-calibrated should the front-end gain or bandwidth change. In this case the NAR mode has advantages. Callisto has designed radiometers working in X-Band and Ka-Band ground stations.
Typical specifications are as follows:
| Parameter | Specification | ||
| Total Power Mode | Noise Adding Mode | ||
| X band | Ka Band | ||
| Noise Temperature measurement resolution. | 0.01dBt = 10ms 0.005dBt = 100ms 0.005dBt = 1s |
0.02dBt = 10ms 0.01dBt = 100ms 0.005dBt = 1s |
0.1dBt = 10ms 0.05dBt = 100ms 0.02dBt = 1s |
| Overall Measurement accuracy | N/A | 6 % Rss | |
| Range of Noise Temperatures | X Band: 100K to 200 K | Ka Band: 150K to 75 K | |
| RF Measurement bands | X-Band 8400 to 8500 MHz | Ka-Band 31800 to 32300 MHz | |
| IF Measurement bands | X-Band 540-640 MHz | Ka-Band 420-620 MHz | |
| Measurement bandwidth | X Band: 100 MHz | Ka Band: 220 MHz | |
radiometers, one for ESA, the other for ISRO.
Learn More about:
- Cryogenic Low Noise Amplifiers
- Compact Cryogenic Low Noise Amplifiers
- Control Software Development
- Miniature Cryogenic Low Noise Amplifiers
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