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Tuesday, January 6, 2015

Nick's BITX


Good Evening Gentlemen,

Pleased to report that, inspired by Pete’s help before Christmas, and innumerable comments by Bill over the last few months, I have a working BitX receiver strip – first light about 30 minutes ago on a short length of random wire but still heard a couple of Italian stations.

Followed Pete’s example and built each stage as a module, I used MePads, having noodled the layout, which is far from optimum, but did mean that I could tinker and, more to the point, test each section before I connected it together, so that starting from the amplifiers (Pete’s design), I was able to test the mixer after a bit of thought and then slowly work my way back through the filter, via the amplifier blocks, DBM, and back to the BP filter … Came together surprisingly quickly working as you suggested Pete, and nice manageable chunks too. I think about 2 hours for each module to noodle the layout, test it and document what I’d done.

Still lots to do, using a semi commercial BP for now as I need some bits that I’ve ordered to build a homebrew BP filter, the crystal filter isn’t optimised and just uses Fahran's suggested values, nothing is properly tweaked so far, but, it does work – thanks guys !!

I’ll follows Fahran's suggestion and tinker with it on rx for now, might build a VFO so it’s ALL discrete devices. Currently all 2n3904s except for the 2n3906 in the audio stage, and of course the Chinese DDS with an Arduino so I have followed the path that Bill set out a while back – it’s a little deaf against my FRG7 so far but tweaking the filter to match the impedances a little better will probably help, and the filter has a lot of ripple.

Next stage will be to build a microphone amp and test it on the Tx side, then tackle a small linear amplifier for it, I’ll stick to around 5 watts for now, and inevitably, I can see it being tinkered with in the course of time.

VERY pleased – thank you both for your help and inspiration

73s

Nick, G8INE



Hi Nick,
 
Congratulations – very nice looking and the other bonus of building it large the 1st time through is when you build the 2nd one –you 1) know the circuit works and 2) you can optimize the layout. I frequently said that I often build two of the same, learning from the 1st and applying to the second. See below. Version 1 was a larger board in comparison to the whole radio in version 2.
 
Bravo – in short order you should be making lots of QSO’s
 
Pete N6QW


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