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Hardware

How to build a radio with the M2k

Background In order to be able to process radio signals with ADALM2000 is necessary a receiver that can convert the incoming RF signal to a lower intermediate frequency. The FM signal, centered on a carrier frequency with high values, is reduced to an intermediate value, called IF, through a downconverter receiver. The receiver built for the m2k-radio has a basic radio architecture with four main components: Antenna, Low noise amplifier, Mixer and a Local oscillator. These 3 main parts need additional components (usually some filters) in order to work well together and receive signals in certain desired bandwidths.

Figure 1. Block Schematic of the M2k Receiver

Low noise amplifier: Because antennas are sources of weak signal, it is necessary to amplify the signal received through it but is also important to keep the noise level as low as possible. For this purpose, is used a low noise amplifier which amplifies a low power signal without introducing additional noise. As FM radio has a 200kHz bandwidth, from 88.1 to 108.1 MHz is important to use an LNA with a bandwidth that includes these frequencies. Mixer: A well-suited IC component for RF to IF down-conversion applications is the AD831 Low Distortion Mixer. It consists of a mixer core, a limiting amplifier, a low noise output amplifier, and a bias circuit. The mixer produces a high-level output at IFP and IFN—consisting of the sum and difference frequencies of the RF and LO inputs. Local Oscillator: The Local oscillator of this receiver can be implemented using ADF4351 component. This is a wideband synthesizer with integrated VCO which allows implementation of fractional-N or integer-N phase-locked loop (PLL) frequency synthesizers when used with an external loop filter and external reference frequency. The optimum LO frequency and power can be software programmed on the ADF4351.

Hardware setup: For building a first prototype, it is possible to find each block in the form of an EVAL-board which has all the necessary components already integrated and is ready to be easily used in the project. The blocks are interconnected with SMA connectors. The filters between the blocks can be used to reduce the unwanted frequencies so the acquired signal is at a better quality.

Figure 2. EVAL Boards

The last thing necessary, from a hardware point of view, is the power supply. Using an external supply and some voltage regulators is possible to implement an easy solution. In this case, with a 12V supply and simple voltage regulators together with their bypass capacitors you can implement the 5V and 9V supplies needed for the boards.

Figure 3. Power Supplies

The outputs of the regulators should be connected on the corresponding VCC pins/pads of each board (5V for LNA and PLL, 9V for the mixer).

Connections to M2k

1+ - AD831 IFout
  1- - AD831 GND (outer part of the SMA connector)
2+ -
2- -
W1 –  
DIO0 - ADF4351 CLK
DIO1 - ADF4351 DATA
DIO2 - ADF4351 LE
DIO3 - ADF4351 MUXOUT

Figure 4. M2k Pinout

Figure 5. M2k Radio Receiver

Software

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