Dave, GØRMF, long time LF proponent and ardent home-brewer has recently posted construction details of his new 630m transmitter.
It is a readily reproducible design that may be of interest to those looking for a transmitter capable of developing full ERP power output.
From Dave's description:
This amplifier is based on the ‘300W Class D Transmitter for 136kHz’ published by the RSGB in Radio Communication and reproduced in the LF Experimenters Handbook by Peter Dodd G3LDO.
This circuit, updated and modified for 630m, uses 2 MOSFETs in push pull driven by square-waves from a CMOS D-type flip flop. The power can be varied from around 25 to 300W by increasing the supply voltage over a 12 to 32V range. Circuits are included to protect against excessive supply current and high reflected RF power.
The amplifier is suitable for any non-linear mode. Examples include CW, QRSS, WSPR, JT-9, JT-65 and FSK.
The circuit has been built on a dedicated double-sided PCB measuring 164 x 120mm. For ease of construction 90% of the components are leaded but it has been necessary to use a few surface mount devices as the normal DIP versions of some ICs are increasingly difficult to find.
In many respects, this circuit is similar to my own homebrew transmitter which can be used on both 630 and 2200m. Although Dave has built his circuit on double-sided PCB, the project would be equally at home on one-sided board or even constructed 'Manhattan' style, the method I chose. This latter style lends itself to easy component swapping to optimize circuit performance.
|VE7SL 2200m / 630m Manhattan-style Transmitter
In addition, Dave's website contains several interesting circuits that might be of interest to those getting started on 630m.