When you want to observe a 6.8 GHz Carrier with a budget-friendly frequency counter, then this nifty thing is your friend. It can divide by 80, 160, 320 and 640. This will move your UHF into the HF range, so you can monitor it by e.g. a PicoScope™. Design was inspired by our colleagues in Lausanne. The enclosure is a SucoBox™.

Supply was 5.1 V using approx. 75 mA. RF-level should be 0 dBm ±5 dB

The overall Division Ratio is a combination of a fixed part (:8, HMC434) and a variable part (MC12080). By soldering resistors R1, R2 and R3, the logic levels at the input of the second prescaler are set. The naming follows the datasheet. If no resistor is asssembled, all inputs are LOW and the Divide Ratio is 80 * 8 = 640.

Please note, that the minimum frequency is somewhere near 250 MHz.

The output of the Prescaler is slightly too low to be directly connected to TTL circuits. A buffer with some gain is necessary. The datasheet specifies a typical output voltage of 800 mVpp up to 350 MHz, decreasing to 450 mVpp at 550 MHz.

We usually use a Buffer made with a BFR92A (Rc = 360 Ω, Rcb = 3.6 kΩ), capacitively coupled at the input, dc coupled at the output. Supply is 5 V. In this case a frequency counter shall be used, so we did not add that.



Output at 10.625 MHz (6800 MHz : 640), as seen on a Scope

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