Our 472 KHz 630 metre preamp is based on G3YXM’s design from The RSGB’s LF Today book. We adapted it slightly to better suit 472 kHz (630m) from 501 kHz (600m) among other slight changes.
The schematic is as I made mine. Note that the Toko coils T1 and T2 are 455 kHz IF transformers, with the internal capacitors removed as they won’t cover 472 kHz alone. C1 and C2 are then selected to resonate with T1 and T2 on 472 kHz. C1 and C2 are usually either 120 pF or 150 pF. 120 pF gives a better range with the ferrite slug on the transformers.
Below is my PCB for the receive pre-amplifier:
The images above are scaled at 600 DPI. They are also available as correctly scaled PDFs which you can print at 100%. Use these masks to create the boards via toner transfer or photolithographically. I have also included the Gerber files if you are using a plotter/milling machine or having boards made.
|Bottom Copper PDF
|Silk Screen PDF
|Gerber Files ZIP
The image below is of the prototype 472 kHz receive preamp. The masks above have some slight alterations and improvements.
The improved board design was tested out by getting Dave (G7UVW) to built it, which he did without problem. Dave seemed to have good results.