Nothing revolutionary here, just using bits i have sitting doing nothing. QPRlabs si5351, nano, oled and encoder make up the frequency generation module for my test bed. I have the next one mostly done also, the audio amp.
Now i mostly work in SMD and design board for things I would like to test. But i do have a lot of through hole parts still that are sitting there pretty much doing nothing, so I started thinking of ways I can use them up and I think I have a solution. Anyway, I have a whole bunch of ideas I would like to try, different circuits to built, test and assemble into working transceivers. Back in the day, which day, ummm, ye olden day LOL, hams would breadboard circuits using actual breadboards. My idea here borrows on that concept and brings it into the modern age.
Starting with the baseboard, rather than mums old chopping board we have a PCB that has 2 power rails for 12 and 5v, a bunch of bypass caps, a DC barrel jack for power input and a 5V regulator. Lets face it, most of what we do only has 2 power rails and those are the most common. Along the baseboard we have 2 rows of dual 10pin headers for our plugin modules to slot in and out of. Each header has 2 power, 2 ground and 6 unused pins for moving signals between the plugin board. Making for neat and tidy wiring.
The prototyping module boards connect to the baseboard with right angle header pins. Either dual or single row header pins can be used, I used single row so i can easily wire stages to the header pins for routing between board on the baseboard.
The tops of each board can be locked together using brass standoffs. This makes for a modular system you can plug and play, mix and match different circuits for testing and characterization.
The backside of each module board contains grounds top and bottom as well as power buses on each side to make veroboard type prototyping nice and simple. This system should allow for quite interesting builds to be achieved one stage at a time.
Lots of people say they have a hard time soldering. Well, I wear reading glasses because my eyes are not what they used to be and my hands are fucked with arthritis, i have only 55% use of my right hand and 70% in my left hand. It is what it is and they are only going to get worse over time, so no use bitching and moaning about it, i just get on with living as much as I can.
So, soldering, here is the tip and only the tip mind you (AVE HAHA) bright white light so you can see, and extra magnification. Even as a handycapped I am working with SMD components, I just magnify things enough and use the right tools. And the tools being different shaped tweezers and a nice thick 3mm chisel tip on the soldering iron. Yes, that big chunky tip is the key to things, you want to hold as much heat in the iron as you can. Use thin solder, 0.6mm or thinner because a little dab will do ya (AVE) and with heat in the tip, you are not spending time heating things up, just dab and go, dab and go. Tack one side of the part, lay the solder over the other pad or pads and dab the iron and its done.
The parts I use go down to 0.2mm pin pitch, SOT23 and 0802 in passives. I stay away from BGA and other leadless parts, they just suck, but everything else is pretty much good to go. So don’t be afraid, just illuminate and magnify, if you can see it, you can solder it. OH and flux the fuck out of it HAHAHA, flux will make you a winner.
Well, the saying goes, 3rd time lucky. In my case it is 4th time, well 4th version of the design and 3rd time I have had boards made for this. The good thing is, it works this time. There are not masses of strays floating about anymore. They are just about all eliminated. You can see by the gain plot that its nice and linear with 0.5db loss from 1 to 30mhz. That is good enough for me. The losses are actually a little less than that, because i did not calibrate out the cable losses, but lets call it good enough for the kinds of girls I go out with.
Now its just a matter of rewriting the software to account for the changes I made and then putting it to use. Next version will have the capacitace switchable from low Z to high Z and there will be an SWR bridge and probably auto tuning. For now, i will finish this off and put it to use with some other home brew bits I have here.
I was bored yesterday so i thought i would try building an amp from these transistors I have sitting in the box. Ummm yeah I smoked it pretty hard before I even got any significant power out. I think the main thing is that I could not drive it hard enough to get it into the linear region and I might have had a bit to much bias happening. I will try again, but from what I was reading online, these transistors have a habit of wanting to detonate.
Looks pretty dont it LOL. Well it does not work. Why you may ask, well, the IO expander which was meant to be able to output 5V and 20ma per pin, could not raise the skin off a custard. 1.2V out into an open load is all i could get out of it. I do not know why, schematic is correct, the voltage is correct and the reset line is pulled high, I can read and write to the IC over I2C and turn the pins on and off, they just never get anywhere near being 5V out. Anyway, I have redesigned the board using only the pins on the micro to control the relays, having bodged some wires into it to make sure it would work.
I also have another iteration in the pipeline, were I have added some switching of the capacitance to either the input or output sides for low z and high z loads and have also added swr meter circuitry. It might be months before i have that totally ready, I am going to spend a lot more time on the layout to get it right.
Air variable cap parts arrived a couple of weeks ago now. Have had this sitting on the bench for over a week, thought i should post about it. These are the panels, i separated them by cutting the tabs off on the bandsaw. If i ever make a second iteration, I will add in some drillings to make the tabs break off.
6 plates top and bottom give a minimum capacitance of 20pf.
Fully meshed they give a maximum capacitance of 133pf. Using the parts on hand, I have enough plates to build 2 capacitors that are 60 to 400pf or there about’s, being 15 plates top and bottom. Its just a matter of spending the time assembling them. There are some changes i would make if I was to do them again, like make the rod 5mm rather than 4mm, this would make it easier to mount a knob on and things like that. There is a spring front and rear to apply resistance to the movable plates so they hold their position. Other than that, it works.
I have had the parts and boards for this sitting here for quite some time. After posting all the schematics and board files for everything i had working, i took a few weeks off to chill and regroup. Actually I have been racing F3 in Iracing and having a really good time. So anyway, today i got keen and thought i would assemble this board to see how i went. Other than leaving the DC blocking caps off and having to bodge them in, the board actually worked well. It has been sitting on the bench running for the last 30 mins and its barely gotten warm. Talk about some efficiency in these modern transistors. Signal source is an SI5351a and so square wave in and square wave out. This thing will chooch 5w all day without a problem. I was not sure it would work well, the fets are speced for UHF and I am using them at HF. I have the big brother to this fet and it will do 20w, so when i get brave I will have to see if i can make more power.
This has been a fun little journey. What started out as look at me i can WSPR on one band, is not looking like, look at me I can WSPR on 5 bands. So what we have here is the 3 band WSPR TX that does 20, 15 and 10m and with an extra PA board and a little bit of code i can add 80 and 40m into the mix also, all this from just 2 antenna.
Here is the schematic for the PA board, less the power supplies. It requires 7V for the fets and 3.3V for the bias. The 10K pots and 3.3v bias supply allow for really fine changes in bias voltage. If memory serves me correct, 600mV was enough to run the fets at about 400mA draw each. The fets themselves are for VHF to GHZ range, so running them at HF is not ideal but its all about what you can find. These are 50 cent parts and what is used in many dual band HT’s as their 5w PA. The fact that I am getting 5w out at HF is rather nice.
Here is the PA board sitting in the box I made for the never ending story transceiver LOL. Note the 5A buck converter being used for the 7V power supply.
Here is a more broad view of how things are looking. 2w out using the old LPF board that was more loss than pass. Built new filters and things are now much better.
Fresh built LPF board without the losses of the old board means I am not wasting 1/2 the power in the filters. I was always going to be happy with a couple of watts, but the fact its making 5w, is nice. Note the heatsink stuck to the back of the PA board. A tone of vias are uses to wick the heat away from the fets and into the heatsink. Its been running for 24 hours straight and temps have remained steady around 50deg C.
Close enough to call that 5w. Its a little less on 20m, more like 4. But that is ok.
And finally, no spots on 15 or 10m, that is to be expected, but we have a number of spots on 20m. So i am calling this a success. Learned a bunch thought this project and the outcome was better than I expected.