Portsdown NF Meter

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The Portsdown 4 includes a Noise Figure Meter (STILL UNDER DEVELOPMENT) that uses the LimeSDR Mini and a user-provided noise source and custom switching power supply to provide an indication of the performance of preamps and transverters. It is hoped to describe this emerging capability in CQ-TV 274 (Winter 2021). This Wiki page is purely to inform the early beta testers before the capability goes on general release.

General Principle

The limiting factor on the performance of many microwave receivers and some VHF receivers is the amount of noise generated by the inout stage of the receiver. G8GTZ discussed this in his excellent talk to CAT 21 CAT 21 Video which is essential viewing before trying to use the Portsdown 4 Noise Figure Meter.

The input stage noise can be estimated by making comparisons between the receiver output with no input, and its output when connected a calibrated low-level noise source. This is the method used by the popular HP Noise Figure meters and the method used in the Portsdown.

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