Test & Measurement

RF receiver offers adaptive preselector

16th October 2015
Mick Elliott

An RF receiver providing a high performance solution for the interception of RF signals has been introduced by IZT. Instead of standard solutions with fixed filters, the R3500 offers a highly linear, flexible preselector with electronically configurable start- and stop frequencies. Modern, automatic signal classifiers are able to simultaneously analyse several MHz of spectrum for any signals of interest.

The interception of the high frequency (RF) signals poses an exceptional challenge for the dynamic range of any receiver, especially when large and sensitive antenna systems are used.

Management of the RF energy reaching the AD converter by means of an analogue preselector is essential. Typically a bank of sub-octave filters is the standard approach for reducing the total signal power and second order intermodulation products. Due to its fixed centre frequencies and bandwidths, a sub-octave preselector lacks the flexibility to deal with different receive scenarios.

This comes at the expense of inflexible filter bandwidths. The IZT R3500 instead offers a highly linear, flexible preselector with different combinations of high-pass and low-pass filters. The preselector implemented in the IZT R3500, allows the user to arbitrarily select a combination of one high-pass and one low-pass filter. These filters are then cascaded in the signal path electronically, but completely passively with no amplifiers in between.

Within the input frequency range of 9kHz to 40MHz, a pool of high-pass filters with corner frequencies spaced in a ratio of approximately 1:1.26 can be selected. This limits the amount of incoming signal energy and provides highly effective protection against unwanted IP2 products.

The user can freely cascade one out of 12 high-pass filters with one out of 13 low-pass filters. In a very large signal situation, they can be combined to resemble a highly selective sub-octave filter bank.

For broadband, automatic signal search algorithms, a bandwidth of several megahertz may be best suited. In a low power RF environment, the filters can be switched off completely. The receiver supports up to four sub-channels as IQ, complex FFT or PSD data over Ethernet. The sub-channels can be placed anywhere within 9kHz and 40MHz. Signal processing, data format and control interface of the IZT R3500 are fully compatible with the IZT R3000 series, giving current users of the IZT R3000 receivers an easy migration path. The Ethernet-based signal distribution of the receiver can eliminate costly multi-coupler structures, which provide an analogue interface between the antenna and a variable number of receivers. Instead, the IZT R3500 digitises large parts of the RF spectrum in very high quality and the signal distribution is lossless and completely independent within the digital domain.

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