You met my prototype in this post, where I promised that, once the commercial kit was ready, I would "post the complete schematic, in true open-source spirit".
Well - here it is...
As you see from the schematic, the shield hosts not just George's transmitter circuit but also a power supply (to derive 5V system power from the "12V" radio supply) and a flexible input buffer/amplifier arrangement, to allow the transmitter to operate with a range of RF signals (including - of course - those from the Kanga / m0xpd DDS Shield).
The transmitter puts out just under 2W - as I confirmed yesterday by sending WSPR signals on 30m which were received in Tasmania (again) and Venezuela!
There are complete design files (including an Eagle PCB design, suitable for single-layer construction - as in the prototype) on the "Occam's Micro" support page.
You can meet the new transmitter shield on the Kanga Products stand at Rishworth.
See you there!
...-.- de m0xpd
Hi,
ReplyDeleteas beginner ham I'm currently building my own shield and as I start to learn more about radio electronics some questions occurs. I'm looking at v1.4 of the schematics.
1. What is the purpose of R5 and its connection to the spare pin on the Arduino shield?
2. Won't C10 and L1 act as a band pass filter for the receiver?
If so, do you recommend a wider filter if I would like to cover 80m to 6m with the same shield which is basically what the AD9850 could handle? Maybe it needs some extra filtering on the TX output.
Best regards
SA5PMG
Hi Markus
ReplyDelete1) R5 takes a buffered version of the VFO signal to the "RF Bus" connector, for use in the matching Receiver System.
2) Yes - C10/L1 should ideally be chosen to resonate at the chosen band. However, I have found the 7MHz version works acceptably at other low HF bands as well, and never bothered to change it (though I do operate mainly at 7 MHz). The single C10/L1 filter is not enough for proper receiver pre-filtering - I suggest a specific band-pass filter for each band.
You MUST use low-pass filtering on the output of these kind of transmitters to reduce radiation at harmonics of the intended operating frequency. These should be band-specific. The amplifier (like most other QRP "linears") is not sufficiently linear to operate without such output filtering.
Thanks, got it including the output filter part.
Delete/Marcus