ZL1BPU exciter

Posted on Feb 4, 2014

Direct Digital Synthesis (DDS) frequency generation has been around for quite a while, but most of the homebrew DDS projects are rather complex and use expensive chipsets. Murray ’s exciter has only 3 inexpensive IC ’s,and the whole thing can be built for under $50. Perhaps best of all, the exciter can be programmed via a PC to operate as a beacon,

 ZL1BPU exciter
Click here to download the full size of the above Circuit.

and the software is tailored for operation using modes that are popular among LF hams and experimenters. Murray ’s article is at and there are also links to a very comprehensive user ’s guide. His writeups are excellent, and you should view all of the information if you plan to build this project. I did a quick check of parts availability in the US, and quickly found sources for all of the ICs. To share the shipping/handling charges and to encourage more US LowFERs to experiment with the modes supported by the ZL1BPU exciter, I offered to purchase up to 10 sets of parts and to make them available at my cost. The offer was quickly "sold out". This article is intended to help those who purchased sets of parts to get their units running, and to provide ideas for anyone else who wishes to build this interesting and useful project. Important Notice: As with any high-speed processor, it`s easy for an undervoltage condition or a voltage transient to scramble the memory on the Atmel AVR chip. One fix for this problem is to add a voltage detector reset chip as described later in this article. Some time ago, Murray also suggested adding a 0. 01 uF capacitor from the reset line (pin 1) of the microcontroller to ground. I found that this fixed a lot of problems, especially the apparent inability to load the EEPROM memory correctly. Unfortunately I never got around to updating the circuit diagrams or including a mention of this fix in...

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