This article is a set of notes to contribute towards the club 475 kHz (or 630m) project. Since the project potentially includes the design and build of transmitters, receivers and antenna systems members are encouraged to contribute ideas and information to this article and spawn different articles as necessary.
CW Transmitters
There are a number of transmitter designs on the web. Most seem to use a 3.8MHz or 7.6MHz oscillator divided by 8 or 16 driving a class D or class E PA. Alternatively a DDS may be used.
Exciters
GW3UEP's CMOS VFO - updated link 12/2/2023
Power Amplifiers
The most popular MF amplifier designs seem to be those by GW3UEP. There are also details of higher power and class E amplifiers available.
- GW3UEP's QRP 1W PA - updated link 12/2/2023
- GW3UEP's 25W IRF510 PA - updated link 12/2/2023
- GW3UEP's 100W PA - updated link 12/2/2023
- M1GEO's developments based on GW3UEP's 25W PA
- KB5NJD - links on his QRZ page since he took his website down - updated link 26/2/2023
- DJ0ABR's 500W PA
- VK5FQ's miscellaneous LF info - updated link 26/2/2023
- VK1SV's introduction to class E amplifiers and a useful component value calculator
- A (very) technical paper about Class E amplifiers (pdf)
Receive Converters and Transverters
There are a few transverter and receive converter designs available, useful if you don't have a receiver that covers the band.
Antenna-Related Info
It's not just antenna designs, we need to consider how transmitter power (roughly) equates to EIRP, and whether our test and measuring equipment is telling us the truth at MF!
Unfortunately, much of the information previously linked here was courtesy of KB5NJD, but it seems to have all disappeared from the Internet now.
- VE7SL has lots of general 630m info on his blog