The AMSAT-DL Downconverter V3 provides a precise 40 MHz reference signal (OCXO or GPS stabilized). One sets jumper F1/F2 to external operation and connects the 40 MHz output of the downconverter to the REFIN input of this upconverter.

The input of the upconverter is very sensitive. To be able to drive it with the lowest power of common transceivers, there is an input attenuator right after the SMA connector. The p-attenuator consists of three resistors.

R1 must withstand the power of the transceiver and consists of two parallel 100 V resistors. Together with R2 (470 V) and R3 (51 V), this creates a 50 V attenuator with an attenuation of about 25 dB. Thus the upconverter can be driven with approx. 1 W (SSB). For special applications (e.g. driving with an SDR) this attenuator can be changed or removed completely. The driving power without attenuator should not exceed 5 mW.