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Wednesday, 19 February 2014

More from my BITX40

Well,

I've started to fiddle with my BITX40 that I am making from the V3B kit I mentioned back here:

http://g0mgx.blogspot.co.uk/2014/02/turn-back-clock.html

I've also uploaded a high res pdf schematic of the 14MHz V3B here:

http://www.qsl.net/g/g0mgx//files/BITX%20VERSION%203%20B%20SCH.pdf

For my version which I am aiming at 40M, I need to change the VFO. Mine is going to tune from 2.8MHz to 3MHz. I did some sums and calculated that I needed about 22uH of inductance. Now that's quite a lot!

I ended up winding 62 turns onto a T68-2. Here's the VFO part of the circuit built:


Now, the FLL/counter comes already built. It connects to the output of Q17 - when I connect there I get no results from the counter, but when I connect to Q6 it works fine. The output of Q17 looks like this on the 'scope:


The waveform at Q6 is the same, just slightly larger amplitude - strange - almost like there isn't enough drive at the FLL/Counter connector. I've decided to worry about this later and move on.

This is the FLL/Counter looking at the VFO output at Q6:


I've programmed the counter to display the IF - VFO frequency.

I've also made the Band Pass filter as I discussed back here:

http://g0mgx.blogspot.co.uk/2014/01/gluing-some-old-bits-together-to-make.html

and the 1st RF amplifier is built too:


So far, so good.

Fun, egh?

** UPDATE **

I found that I had the voltage regulator in the wrong way round! I've corrected that and the output at the FLL/Counter point is now slightly higher amplitude and is driving the counter OK. Odd?

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