I honestly do not remember who i stole this circuit from, other than it was somewhere on the internet. If anyone knows whose work it actually is, I will credit them. I have been sitting on this board for about 12 months. The first time I tried to build I made the pcb on the cnc machine, it did not work, i think it was because the footprints for the J-Fet were actually wrong. Anyway, I redid the schematic in Diptrace and sent the gerbers off to have them made. And well it works. The output is not the cleanest, the inductor I used needs more inductance to pull it further, the varactors i used are only 20pf each, needs more capacitance to pull further and the crystals are just random 10mhz ones out of the parts bins, not a frequency i actually care about. But, it works and that is something.
So you wanna be a champion? I have been thinking for a while about documenting this whole process from start to finish for sometime. Often, i only post up bits and pieces of what I have been playing with and never really showing the end result. Sometimes it works, other times its a dismal failure, er….. learning experience. And lets be honest, there are more learning experiences that there are usable widgets at the end of things here.
As pretty much everyone knows, I am not an EE, I am not even an expert, I am just an idiot who is having a go and trying to learn something and if I manage to succeed a few times along the way, then I am happy. So if you are the kind of expert who trolls the internet looking for things to be an expert on, keep on walking, ain’t nothing to see here for you, the same goes for the experts who like to tell everyone how they did it wrong, but never publish anything they do. But for everyone else, stick around as I hope this might actually be an interesting series of posts.
Now the worst kept secret in the world is what I am actually building. Its a single band hand held for either 20 or 40m. In fact, I have been working on this for quite a while and in this post, I am going to outline many of the initial decisions that were made a couple of months back in discussions with some friends. Ultimately, this is a build for us based on what we think is going to be good enough to do the job and fun enough to use more than once. And seeing it is me doing pretty much all the real work in the design and prototyping, its also got to be within my skills to be able to achieve.
So lets start right at the beginning outline what we are going to build, outline the specifications, design considerations and constraints because many of these considerations are going to influence many of the decisions that get made further down the track. So the initial design specs ended up looking something like this:
Form Factor: Hand Held Walkie Talkie
Band: 20 or 40m frequency agile, full band coverage
Receiver Topology: Direct Conversion
TX - RX Switching: Relay
Frequency Generation: DDS, PLL Synth
Power: external 12v internal 3S1P or 3S2P 18650 Lipo
Antenna: BNC connector for Coil Loaded Whip or external resonant antenna
Total Build Cost: Less than $50Aud, excluding battery and antenna costs
To be somewhat modular so the design can be expanded to Superhet SSB at a later stage if desired.
Potentially change the design later into direct conversion SDR for SSB.
Use popcorn and try and avoid exotic parts.
Be potentially manufactureable with minimal labor inputs.
What was doing to constrain much of the design was the case. Was there something off the shelf that would be usable? Could I design PCB’s small enough with everything on it to fit in such a confined space? I will be honest, I have never ever mastered the skills of QRP Labs who can pack so much into such a tiny space. That kind of layout takes some skills and I currently do not have them, anyway, back to the story about the case.
In my box of crap I have bought with the intention of one day using it, I have this plastic walkie talkie case. Its almost the right size and if I went with a AA battery pack rather than 18650’s and also made it much lower power say about 2w, it would probably do the job. But with 5w out you have to get rid of a lot more heat, not a lot of room inside there for a heatsink of any sort other than say a piece of bar stock. So i ruled out using this case. Actually, once i am done with this project, I am going to go back to that case and using the boards i have developed build a pair of walkie talkies on 40Mhz that output less than 1w for my grand sons to use and play with. 40mhz here is a LIPD allocation here and power limited to very low EFRP.
So what i decided i would do, seeing there were not cases off the shelf from mouser that were suitable was to mock one up in aluminum sheet metal using the bending break. The dimensions i used are based on common off the shelf sizes of aluminum RHS that I can buy from a supplier just up the road from me. The external dimensions are 70x50mm, which is kind of chunky, but will allow some wiggle rooms for stuff while im still working out how to best fit everything in there. Ideally, 70x35mm would be a better size, but i might run out of room when i start putting in things like speakers, LCD screen and the like.
In fact, the whole mechanical design is probably one of the more difficult aspects of the build. You need to think in 3d space and think about will this part fit underneath the bits on top of it. The way I have designed things thus far requires the PCB board to stack on top of each other. There are 3 boards in total, the PA board, the Receiver board and the Power and Digital board. This will be compacted back to 2 boards, by putting the digital stuff on the backside of the receiver board. You can see in the above picture the first receiver board i designed. It had some issues that were not easily resolvable and some of the SMD electrolytic cap footprints were just plain wrong. So it was scrapped early on.
Anyway, this post is becoming rather long, and I have been writing it on and off for the last 2 days. I have version 2 of the PCB’s arriving in the next few days from China. I will get to building the receiver board and making sure it all works as it is meant to. And in fact, part 2 of this series of posts is going to be all about the receiver board. Lets hope it all works and part 2 of this is only a couple of weeks away, not a couple of months while i solve problems and fix boards.
Well its been coming for a while and today is the day that its been achieved. I am no longer a radio amateur. I am an electronics enthusiast. Yep, I am done with the people. When you have groups that lie, cheat and exploit for their own end, get exposed time and time again and other groups to gutless or hamstrung to be able to deal with it in a manner that will fix the issue once and for all, I figure, why bother. I am better than all this and so I am out.
I have some really good radio projects in the pipeline that will be released over the next 2 to 12 months. I am currently working on a 5 watt DSB hand held. Tonight I have laid out the Transmitter board, I have some fixes to make to the receiver board and I can sent those off to china to get made. I hope to have the whole project competed by the end of the year. And having quit just about all social media, I should be able to, with some luck, achieve that goal.
To just another form of CB
Marketed to shoppers
Spoonfed carton ham radio like sheep —Paraphrased, Jello Biafra.