Top Band ARDF Receiver using dual gate MOSFETs

This is the second iteration of my ARDF receiver. See Background for the reasons why I decided to build this and the inspiration for the design.

PCB made using the toner transfer method.

Shown with Loop aerial attached. The lower board was a homemade network analyser made redundant by the nanoVNA repurposed to provide the VFO and BFO it contains an Si5351a.

Improving the gain

The DF hunt on 11 July took place in some woods just after several heavy rain showers and I noted that the gain of my receiver was not sufficient to get a distinct null on distant stations. My first plan was to add another stage of IF gain but I realised I wasn’t getting the voltage I expected at gate 2.

With gain set to max on the arduino I measured 2.72V at the point marked IF gain, at pin3 (Gate2) I measured 1.05V and 1.07 on the antenna amp stage.

Changed R11 from 100k to 22K now Vgate2 was 1.42V. This didn’t improve things. Gain was increased for lower values of gain setting but the gain at max voltage didn’t improve and there was more noise.