This handy instrument measures frequencies from 50 MHz to 3 GHz with an accuracy of 10 ppm and provides an indication of the signal level over a range of –40 dBm to +10 dBm. Readings are displayed on a three-line LCD module, and the instrument is powered by three standard AA cells. Here are the bare PCB's required for the assembly.
Frequency measurement is essentially based on a counting method implemented in the Altera Max-2 CPLD. The frequency measurement accuracy essentially depends on the accuracy of the reference signal. The readings cannot be more accurate than the oscillator frequency.
An LT5538 logarithmic signal detector IC from Linear Technologies is used to measure the signal level. Along with a frequency range of 50 MHz to 3 GHz, the selection cri- teria for this device were a dynamic range of at least 50 dB, an input sensitivity of –46 dBm, operation over the industrial tem- perature range of –40 to +85 °C, operation from a 3.3-V supply voltage.