BITX40 RX Test

Well,

I hooked up the bits and bobs needed to test the receiver of my new BITX40 V3B kit, here's what I heard:

Good egh?

There's a whole lot of BITXing goin' on

Well,

I've been fiddling some more with my BITX40. I've nearly completed the exciter board and have been playing with the set up of the BFO and the crystal filter. This is where a spectrum analyser really comes into it's own.

Initially I modified the BFO and removed the inductor - the purpose of the inductor is to lower the BFO below the crystal frequency - this is needed in the BITX20 as we need to retain the USB. As I want to keep the LSB in my 7MHz radio, I need the BFO to be higher than in an USB rig.

Here's the carrier or BFO output (in purple) on top of the save I did of the crystal filter sweep - now I don't much like the dip in the top of the Filter sweep, but I can come back to that later.

Now, here the BFO adjustment is at it's lowest frequency and I looked very much to me like this wasn't low enough. Here is the same thing with 1KHz of audio mixed in too:

So, to move the BFO down a bit I have added in the 15pf capacitor in the original design which is in parallel with the trimmer adjustment of the carrier:

Now, this looks close to perfect to me.

So I adjusted the balanced modulator to get as much carrier suppression as I could:

I think this could be way better if I actually matched some diodes, but I don't think it's going to matter a whole pile. Now if I look at the signal on the output side of the crystal filter with all these adjustments made it looks like this:

Which I reckon is as near to perfect as I am going to get.

Here's a recent picture of the board:

So now I need to move and test further into the circuit. We now need to take this 10MHz output of the filter and mix it with my VFO to make the 7MHz LSB signal I am after. So here is the output of the Band Pass Filter in TX:

and here on the 'scope:

Looking like a very nice clean signal at 7MHz to me!

Good, egh?

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?

Turn back the clock!

Well,

I started a project a while back here:

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

but then I became a touch distracted by the Minima!

So, when I was fiddling with the DDS VFO at 17-17.2MHz I ordered a BITX V3B kit from Sunil in India:

http://amateurradiokits.in/

Now, what arrived in the post has simply astounded me:

So I have a case, a microphone, a complete FLL stabiliser/frequency counter, a PCB set, all the components, wires, interconnects, meter, plus the other bits I can't remember!

This cost me the sum of $125 plus $45 shipping - quite incredible.

There are some good pictures of the finished article here:

http://cqbitx.blogspot.co.uk/

So, as I have a FLL stabilised VFO with the kit, I could move that to 2.8-3MHz and use it with a 10MHz IF to get to the 40M radio I am wanting instead of the DDS I was planning....

Much to fiddle with!

Good, egh?