Satellite-communications (satcom) systems count on components and subsystems that perform at high levels and simply do not fail, since service for the space-based parts of the system is not a practical option. As a result, testing at the component and system levels is critical and requires satellite-to-ground and satellite-to-satellite link emulators such as the SLE9000 series from dBm Corp. Available for testing at the intermediate frequencies (IFs) of satcom links, these link emulators can truly exercise a satcom system to better understand how it will handle a wide range of propagation delays, path losses, signal fading, signal phase shifts, and even Doppler shifts from moving satellites. The emulators are suitable for evaluating both satellite payloads and earth terminals and available with several options, including built-in multipath-fading and noise-generation capabilities.

The three current base models in the series are the SLE9072, SLE9125, and the SLE9250, which operate at IF center frequencies of 70/140, 140, and 950 to 1450 MHz, respectively (see table). The IFs occupy 1-dB bandwidths of 72, 125, and 250 MHz, respectively, with maximum delays per channel of 1490, 890, and 447 ms, respectively. All three models can be equipped with 1, 2, 3, or 4 independent channels. They operate with maximum RF input power of 0 dBm and provide maximum RF output power of 0 dBm. The link emulators are specified for in-band spurious suppression of better than -45 dBc for a 0-dBm input signal; the typical performance is more like -55 dBc. These link emulators feature clean internal signal paths, achieving a typical noise floor of -138 dHm/Hz.

Based on their use of analog and digital signal processing, the SLE9000 satcom link emulators achieve impressive results. They achieve static delay resolution of 0.1 ns and dynamic delay resolution of 0.5 ps, with relative delay accuracy of 1 ns along with any errors added by the 10-MHz system reference. Doppler shifts can be added over a total range of 3 MHz for all three models, with resolution of 0.01 Hz. Signal attenuation, via the "old-fashioned" analog attenuators, is adjustable from 0 to 40 dB with 0.1-dB resolution and accuracy approaching 0.25 dB.

The SLE9000 series link emulators can be controlled by means of a touchsensitive front-panel display (see figure) and keypad or by remote control via an IEEE-802.3 interface. The instruments are supported by SATGEN software, which uses link models to generate data files for the SLE9000 instruments to simulate the complex communications paths between satellites and ground stations and between multiple satellites.

The SLE9000 series emulators can be configured with different options for multipath fading and AWGN capability, as well as with external frequency upconverters and downconverters for testing satellite systems at a variety of different frequencies, including at C-band, S-band, X-band, Kuband, and Ka-band. dBm Corp., 32A Spruce Street, Oakland, NJ 07436; (201) 677-0008, FAX: 201) 677-9444, e-mail: info@dbmcorp.com, Internet: www.dbmcorp.com.