Frequency downconversion is the basis for virtually all RF/microwave systems, whether they are involved in commercial communications or military surveillance. Ideally, a frequency downconverter covers a full input frequency range of interest, translating these signals down to a range that can be examined by analysis equipment for test purposes or digitized by a high-speed analog-to-digital converter (ADC) for communications and demodulation purposes. A line of wideband frequency downconverters from Elcom Technologies (Rockleigh, NJ) comes close to that ideal performance by leveraging the company's expertise in fast-switching frequency synthesizers to provide low-noise downconversion of wideband signals through 40 GHz over a wide dynamic range.
The SIDC-MW-WB wideband microwave downconverters and tuners (see figure) can be ordered with frequency coverage of 0.5 to 7.0 GHz, 0.5 to 18.0 GHz, 0.5 to 26.5 GHz, and 0.5 to 40.0 GHz. They can achieve 10Hz tuning resolution over those ranges, and can tune almost instantaneously due to maximum frequency-synthesizer local-oscillator (LO) tuning speed of 100 µs and as fast as 50 µs in scan mode. The downconverters can perform sweeps from one user-set frequency to another in sweep mode, and can tune among as many as 512 frequency channels in scan mode. Sweep rates can be as fast as 1 GHz/ms, while step times can be adjusted from 1 ms to 60 s per step, or programmed to stop upon detection of a given signal and level.
The broadband frequency downconverters are designed for operating temperatures from 0 to +60°C and achieve better than ±0.1 PPM frequency accuracy with temperature as a result of a stable 10-MHz internal crystal reference oscillator. The long-term stability derived from this internal reference is better than 1 PPM/yr. For those who require better frequency stability, the downconverters include a port for connection of an external 10-MHz reference oscillator with 0 ± 3 dBm output power.
Because Elcom Technologies is known for its fast-switching, low-noise frequency synthesizers, these frequency downconverters might be expected to offer good phase-noise performance, and they do not disappoint in that respect. The typical phase noise offset 100 Hz from the carrier is –70 dBc/Hz, dropping to –85 dBc/Hz offset 1 kHz from the carrier, –90 dBc/Hz offset 10 kHz from the carrier, –100 dBc/Hz offset 100 kHz from the carrier, –120 dBc/Hz offset 1 MHz from the carrier, and –140 dBc/Hz offset 10 MHz from the carrier.
The RF section of these frequency downconverters is designed to handle maximum RF input power levels of +20 dBm without an attenuator. The analog RF/microwave front-end signal-processing components combine for gain flatness of ±1.5 dB across the full RF input range and worst-case gain flatness of across the full IF bandwidth. The maximum noise figure of the RF front end is 15 dB. An RF input monitor is activated for signal levels as faint as –25 dBc (±5 dB).
Downconverted signals are available at a wideband IF output port and at standard IF output ports. The wideband port is centered at 1.2 GHz with a 3-dB bandwidth of 500 MHz. The maximum group delay for signals within 80 percent of this 3-dB bandwidth is 3 ns. The RF-to-IF gain for this port can be manually adjusted in 1-dB steps over a 42-dB range. The gain flatness across the full IF bandwidth is ±1.2 dB for input signals to 26.5 GHz and ±2.0 dB for input signals from 26.5 to 40.0 GHz.
The standard IF ports are centered at 70, 140, and 160 MHz. The 70-MHz port offers user-selectable bandwidths of 5, 10, 20, 30, and 50 MHz. The typical gain flatness across these IF bandwidths is ±0.4 dB, with worst-case performance of ±0.6 dB. The 140- and 160-MHz IF ports provide user-selectable bandwidths of 40 and 80 MHz with typical gain flatness of ±0.6 dB and worst-case gain flatness of ±0.8 dB across the full IF bandwidth. As with the wideband IF port, a manual gain range with as much as 42 dB can be set in 1-dB steps for these standard IF ports.
The IF ports also feature an automatic-gain-control (AGC) function based on the same 42-dB gain control range, with fast attack time of 10 ms for a 42dB change and 2 ms during frequency sweep or scan functions. Decay times for the AGC can be programmed from 1 ms to 1 s, and IF output levels can be programmed from –20 to +5 dBm in 1-dB steps.
The frequency downconverters promise a spurious-free dynamic range (SFDR) of 60 dB with better than 70 dB image rejection. The wide-dynamic-range downconverters have input 1-dB compression of –10 dBm at a 20-dB gain setting and input third-order intercept point of 0 dBm at the same gain setting. The output 1-dB compression point is +15 dBm while the output third-order intercept point is +25 dBm, both measured at the maximum gain setting.
The downconverters are supplied in a standard 1U-high rack-mount enclosure measuring 1.75 X 22 X 17 in. They can also be specified in an optional VME configuration. The standard operating temperature range is 0 to +50°C while an option (OPT-111) qualifies the downconverters for use from –20 to +60°C. The units are designed to meet MILSTD-461C for EMI and the applicable procedures of MIL-STD-810E for shock and vibration. They are well equipped in terms of digital interfaces, with Ethernet 10/100 BaseT local-area network (LAN), RS-232, and RS-422 interfaces for flexible connections to computers and networks. The downconverters are ideal for a variety of applications, including for spectral management, emission compliance testing, electronic-warfare (EW) systems, flight-line testing, synthetic instrumentation (SI), signal intelligence (SIGINT), and in direct-finding (DF) receivers. They run on 95 to 265 VAC or +28 VDC.