<\/p>\n\n\n\n
This design supports 6 bands and each band filter output can be routed to one two outputs so it can be used multiple antennas. For the filters for each band I used kits from QRP Labs (QRP Labs Low Pass Filters<\/a>) and to switch bands used relays ( under the filters) and yes it owes a lot to the QRP Labs U3s and their relay switch filter board is what gave me the idea to use the small relays beneath the filters.<\/p>\n\n\n\n The firmware is based on code by IW5EJM (multiband nodemcu wspr<\/a>) but with quite a lot of changes and the addition of an OLEd display and web server. The OLED to show me when it last transmitted, on which band and when it last updated its time from NTP it is configurable via web browser. the web server is to enable configuration of which bands are active and to select test routines for setting up and tuning the filters.<\/p>\n\n\n\n Its a pretty standard wspr project with a couple of hardware features worth highlighting:<\/p>\n\n\n\n The 5V Regulator<\/strong><\/p>\n\n\n\n The 5 volt regulator (next to the two diodes) is a murata switching regulator<\/a> that has the same pinouts as an 7805 but has the big advantage of not getting hot when its supplied by 12 Volts.<\/p>\n\n\n\n Processor<\/strong> <\/p>\n\n\n\n For the processor its a Wemos D1(a real one ). A lot of the clones of the D1 have an underated 3v regulator on board. For more on that discussion on clone Wemos boards see this link from bbqkees<\/a><\/p>\n\n\n\n There is room for up to 3 FETs (socketed) but it can manage quite well with just 1 (bs170). I also included an 74HC00 socket in case I want to buffer the Si5351 output in some future experiments. <\/p>\n\n\n\n Debug and Measuring Points<\/strong><\/p>\n\n\n\n All the headers are to make it easy to put a meter in line with the output stage and\/or to feed it from 12V instead of 5V. It makes life a lot easier if at the design stage you add in test points etc. I also added LEDS on the select lines to the relays as that made debugging and config a lot easier. For the LEDS these are small SMD devices. The relay drive transistors could also have been made SMD but I was feeling old school and had a load of through hole transistors in a drawer.<\/p>\n\n\n\n The Drift…..<\/strong><\/p>\n\n\n\n Frequency stability can be a bit hit and miss with the generic Si5351 modules and initialy there was frequently 3-4 drift on 12 mtrs. But there is some (excellent) advice on the QRP Labs web site from both Hans and John Ove (https:\/\/www.qrp-labs.com\/synth\/freqstab.html<\/a>) . My variation was glueing an M3 nut to the xtal and the si5351, and then enclosing the module in some polystyrene. Now it is 0 drift for most decodes and I suspect for those that arent the drift may be with the receiving station.<\/p>\n\n\n\n <\/p>\n\n\n\n Kicad 3 D Impression of the board<\/p>\n\n\n\n And now the real one<\/p>\n\n\n\n WSPR (Weak Signal Propogation Reporting) is an interesting means of studying how radio propogation changes, and many people, myself included, have built beacons. But I wanted one that handled multiple bands. Ultimately I will be using an U3S from QRP … Continue reading ![\"\"](\"https:\/\/www.jontrinder.com\/blog\/wp-content\/uploads\/2024\/11\/jjtwspr.-small-blur.jpg\")
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