![]() Using an SDR as capable as the B200 or bladeRF for such simple tasks might be overkill, but consider what it would take to build such a device from scratch. Obviously, when testing an antenna, the 30 dB pad on the output would be removed. The specified noise-figure for the B200 is “ The B200 or bladeRF full duplex SDRs can be turned into a simple scalar network analyzer by adding a directional coupler such as the Minicircuits ZFDC-20-4L. FFT size, sample rate and other parameters are specified in the GRC blocks shown in Fig. If you look at the controls on the display you’ll see they don’t match a conventional analyzer. ![]() ![]() 1 shows the output from a very simple spectrum analyzer built using GNU Radio companion (GRC). 2: SDR spectrum analyzer GRC block diagram Fig. Sample size is 8 bits each for I and Q outputs. Maximum sample rate is 20 megasamples per second (Msps). The board is half-duplex only, so if you want to use it as a network analyzer you’ll need two boards. It can transmit or receive any radio signal between 10 and 6,000 MHz. The least expensive SDR board is the HackRF One, available for around $300. The B200 is one of the relatively low-cost SDR boards now available that allow bandwidth on order of magnitude greater than that available with the inexpensive RTL2832 dongles. Unlike the cheap dongles, it includes a transmitter that allows it to be used as a simple antenna or filter analyzer with the addition of a directional coupler. As with the RTL2832 dongles, software is available to use it as a receiver or spectrum analyzer. ![]() It is still part of my travel toolkit, but when I can, I make room for an Ettus Research USRP B200. ( See “Software-Defined Radios Help Explore RF Spectrum,” July 11, 2012). Two years ago, I wrote about using an inexpensive RTL2832-based DVB/DAB USB dongle as a spectrum analyzer and receiver. ![]()
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