Introduction

My aim was to build a small (residential back yard), capable, Faraday rotation resistant 70 cm EME station.

Low Noise Preamplifiers

After some research a VHF Design SAV-541 with SAW LNA was chosen. LNA EME SAV541 for 73cm and 70cm bands – VHFDesign.

The LNA provided 20dB gain and a noise figure of 0.2dB. The LNA was paired with a DowKey microwave relay for isolation. As these relays are 24Vdc, a 12V to 24V DC-DC converter is used to buck the LNA voltage.

As the station uses crossed Yagi for adaptive polarization on receive, two relays were mounted in the masthead box with two LMR240 cables feeding a preamplifier splitter in the shack. This amplifier-splitter provides the biasT and Rx/Tx switching of LNA power supply.

Dual Amplifier Splitter

This module provides the LNA power supply through a biasT, PTT control of Rx/Tx, splitting each receive polarization to a AFEDRI SDR-Net dual coherent receiver and IC9700. A HP transfer coax relay allows selection of the receive polarization.

Alternative LNA Configurations

During development of the station, various configurations of the LNA and masthead box were tested. The aim was to provide more gain at the mast head for the shack receive splitter and to provide additional isolation before the LNA.

The best noise figure and adequate gain ahead of the SDR-Net receiver were achieved with the current configuration.

The loss in power divider, antenna harness, Tx/Rx changeover relay and DowKey isolation relay increase the noise figure 0.5dBf estimated.

During the development of my 70cm and 23cm EME station, a number of LNA design were built with an array of modern Low NF- FETs and MMICs. This project will be published shortly. A SAV-541 SAW design was one of the best for 70cm.