Amongst the many areas for development within the beacon, there is one gaping “incomplete” – the output lowpass filter. To date, I’ve been using the original ugly 30m lowpass seen in the photo below...
I had always planned to make a switchable output filter, after the style of the multi-band BandPass filter - indeed, I’d already provided a controlling output on the controller board and already written the code to switch bands. Now the time for the hardware finally had arrived...
Here’s the schematic – it borrows extensively from my BandPass system...
The board layout also exploits the work already done for the BandPass filter – all I had to do was change the central filter area. Here’s the resulting board, without any filter components fitted...
The filters used the design guide published by George Dobbs, g3rjv, which is derived from the work of Ed Wetherhold, w3nqn.
I made up the seventh-order filters specified for both 30 and 40m bands on the first two “channels” of the board...
The final channel is unpopulated (until such time as I decide which band to play with next), as with the BandPass unit. I may even go for a plug-in final filter, to keep my options open.
Here’s the new output filter in situ...
It works perfectly (now I’ve tracked down the accidental short on the output HI HI).
Any readers visiting the Blackpool Rally are encouraged to come and meet the beacon on the Warrington ARC stand (just inside the door, near the Bar – where else!)
...-.- de m0xpd
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