I Have Finally Built Something I Am Proud Of

So a few weeks ago I had sent and email to Pete Juliano asking some questions and showing off the progress of my projects, he commented that my work bench looked way to clean for me to have been productive, well I sent him this picture from this morning when I was hard at working building this project. There is currently CRAP EVERYWHERE.

Anyway, now onto the real story. The first thing I have built and designed that I am actually proud of. It all works as designed and I think i am finally starting to get up the learning curve.

So there is nothing revolutionary here. Its a simple CW transmitter biased Class A all the way. Why class A when there are more efficient biasing schemes for CW? Well, because I want reusable circuit blocks that I can use for DSB, SSB and other modes that require linearity.  The theory of operation is simple. We have an ATMEGA328 that controls an AD8950 DDS module, Q3 is a buffer so the gain stages do not load down the DDS. Q1 is a simple switching circuit. When the key is keyed, it pulls the base to ground, 12V can flow from collector to emitter of the PNP transistor, turning on Q4 and Q5.

I had to switch both of these and you will notice on the build board below a mod wire, as originally I had only one of these stages switching, but i was getting massive leak through. In a future build I will look at a better switching method to improve the overall usefulness of the transmitter and think about adding in some wave shaping and all the fancy stuff.

Q4,5 and 6 amplify the 300mv DDS signal to 10V p-p where it is then amplified by a single FET to around 5 watts. Its simple, but works, and getting those gain stages all working together was not an easy feat, I spend a lot of time in LTspice making them place nice with each other.

Here is a close up of the board. You can see the mod wire on the top side, on the bottom side of the board I cut a trace to isolate it.

This is most of the test setup, using only 1 side of the paddles because my straight key has the wrong size jack on it.

Current draw is around 0.7 amps key down.

Power out is 5w.

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Output on the oscilloscope.

And this is why you should never trust the output on the scope to give a honest representation of the harmonic content of the signal. First harmonic is -40db down and the second harmonics is only -30db down. Not good enough for the kinds of girls I go out with. So I need to spend sometime going over the build and see where added distortion is coming from that was not present in the prototype. When I put it on air later to test it out, I will add an extra 7th order filter to knock those harmonics on the head.

You know what. Its really nice when things start to click and what you build looks and works like the design. I get the feeling that 2020 is going to be a ground breaking year for my home brewing.

Cheers,

Rob.

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-40dB RF Sampler

This is a bit of a redux. The fixed boards arrived today and I was able to build it using the correct value resistors. Got a nice and neat -40db of attenuation and being that the resistors in the top half of the divider are 1w, it should be able to deal with some power being put though it. Its pretty much overkill for the 100 to 200w that I will be playing with, but hey, the through trace will burn out before those resistors will. HAHA. Gain is rather flat to 30mhz. Beyond that, it increases, not sure why that is the case. But, i only do HF so its good enough for the kinds of girls I go out with.

 

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LCD Bezels

One of the boards I have delayed is a bezel for 16×2 lcd’s. If you are like me, you cannot cut a straight line to save yourself and the holes look as crooked as a hillbillies tooth. So i am having these made and it should go along way to making my projects looks a bit better. The silk screen on the other side says VFO B, I am planning a dual screen, dual vfo transceiver in the near future.

 

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PCB Delays

I was looking on JLCpcb today to see the progress of the next set of boards. The boards are done, but the coronavirus is going to delay them for who knows how long at this stage. JLC is saying 3 to 14 days because no one is allowed to move and DHL is closed down, but the Australian government is also stopping all planes arriving from China, and I have no idea how long this might be in place for. So its wait and see, but they will arrive eventually. HAHA.

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40m DSB Talkie Walkie

I usually regret posting about something before I even know its working, I mean this blog is littered with the dead corpses of so many projects it probably should be called Robs Graveyard. Anyway, I thought i would post about where I am at with the 40m DSB Talkie Walkie. Other than having one small thing to test, everything has worked as designed.

Shock horror I know, but mayby after 5 years of killing parts, I am finally getting the knack. I have compacted the boards into 2. Yeah i could fit it all on the one board and in a future edition I might just do that, but for now I see a lot of advantages in keeping all the digital stuff on its own board with header interconnects.

All i am left to do is to send them off to China and have them made, build, test and make QSO’s with it. Wish me luck.

The Main PCB board

The Digital Board: Arduino and SI5351A

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Power Inductor LPF

More things being tested for the hand held project. These are 1A power inductors. I need something much more low profile than a toroid to use in the low pass filter and also something not through hole. So i grabbed these power inductors to test to see how much loss they are going to induce. Turns out they are not all that bad and at least as good or better than the hand wound toriods i used on another board.

Other than the corner frequency being in the wrong place because i used the wrong cap values, the loss is less than 2db and that will be good enough for the kinds of girls I go out with. Oh and the hand wound type 2 iron cores? 3db loss. Go figure.

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HT Receiver

 

Ok, the long and the short of it. It actually works well. And by well, i mean it can hear me talking on the home station, it can make a tone from injected signals yadda yadda yadda.

So what was the problem, well ended up being a dry solder joint, the most basic of all problems. I had pulled it apart, cut traces, did eleventeen other things to it trying to work out why it was ringing its head off and making no sounds, and it turns out the LO input pin was dry and not making contact.

So what next? Well i start to integrate things onto one board now and start actually assembling something I can use to make a QSO with. Wish me luck.

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4.91520 Crystal Filter For CW

So i was talking with a mate about crystals yesterday, he has an old 2m rig chock full of pairs of repeater crystals and the discussion was about overtone and fundamentals and all that. So for shits and giggles I knocked up a test fixture to measure some crystals on the VNA. And with the best crystals I have was getting the typical plot for a crystal.

And one thing lead to another and I built another crystal filter, this time for CW. I kind of did not make my target, of 500hz and was closer to 1200hz, but that is nothing changing the values of the caps cannot fix. Ripple is nice, the best  i have made yet, the shape is acceptable and the stop band is down near the noise floor of the VNA, so all in all its not a bad looking filter and should be usable once i make it narrower.

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Magnifying LED Desk Lamp

 

Just about everything I am building these days is SMD. Parts a cheap, you can get parts that would other wise be hard to find in through hole versions and there are still some large size packages around of nice parts to use that you just cannot find in through hole. And because I am building a hand held, SMD is compact is the order of the day. In fact, going forward I do not think I will be building anything through hole at all. I have really gotten the hang of this SMD stuff.

That said, as you get older, the eyes are not what they used to be. I wear glasses and often when working with smaller stuff its not the size that is the issue, its not enough lighting. I have been using this LED ring lamp for sometime, mostly as an over head light. But of late, I have been using its magnifying lens as well, its 8 or 10 times magnification and for hand soldering SMD parts its really come into its own and I do not think i could live with out it.

The lens is 5 inches in diameter, so you get a really nice field of view, i mean, i can stick my face right up to it and look through with both eyes and see everything I am doing, plus, the LED light is bright and white, with very little shadow, so its just about perfect. So if you are like me and need to get your eyes checked and reading prescription adjusted every couple of years, add in a magnifying LED lamp and make your life that little bit easier. From here the next step if a microscope and I think that is overkill unless you are doing much finer pitched work than this. If i ever want to use some of those really cool leadless package IC’s i might need one, but for now, this will do.

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