I have built projects before with SMD components on them, but this is the first time that I have included SMD components on my own projects. Yeah i know, its nothing extraordinary, its a 5V regulator, but we all gotta start somewhere. Which got me to thinking, perhaps I should do more with larger SMD components and be able to fit more on a board. We will see LOL 🙂
Oh and for anyone who is interested, this is a respin of my band pass filter board using these variable inductors i got. Anyway, all i have done at the moment is build one filter for testing. Testing which still needs to be done, but I will get to that soon enough and post up some results.
Slowly integrating all these bits together in software and currently all the relays are clicking in sequence when I change bands on the control board. If you look closely on the upper right, you will see an updated version of the Band Pass Filter board that uses different inductors and filter topology. I need to populate and test one filter to ensure its right and then build the entire board.
Something that I did not notice was that when I changed Ecad software my mounting hole pattern has changed slightly, so neither of the old filter board designs will stack with the other boards. So i have to redo the low pass filter board and I am going to redo the rf frond end board as well and move things around to make it a little more usable and to make sure the 3.3v regulator has a heatsink on it. With bugger all current running though it, it still gets burn your finger hot and that is not right. I am starting to wonder if these ebay parts are actually dodgy or something.
So i discovered something last week or so ago while building power amplifiers. Its a total pain the the butt to be pulling everything apart to wire in the DMM to measure current when setting the bias for fet devices. Also that the meters in my Chinese power supplies are just about useless for anything less than an amp.
So with that in mind, i grabbed out a couple of analog panel meters that I have had sitting here for just about for forever, drew up some artwork in my favorite 2d design package and then went out into the garage to cut and bend some sheet aluminum into something that resembles a case.
Yeah the case is not my best work, but its perfectly serviceable and does the job that its meant to do. IE it houses and protects the meters. So now i can plug this into the power supply, plug the device under test into this and monitor both current and voltage while keeping my DMM free to be used for other jobs.
Yeah I know that you can use 2DMM and achieve the same result, but why spend a lot on an expensive DMM that is going to sit doing nothing most of the time, when for about $10 you can make a bit of test gear that will be good enough.
To add to the PA madness that is going on here at the moment, I decided today to build one of the 2 QRP Labs 10w PA’s kits i have here. At the risk of inflaming all the QRP Labs fan boys out there, i both love and hate their kits.
I love that they are well thought out, designed and tested and bring a level of professionalism to the whole kit process, but, and this is the clincher for me, they are mostly a total pain in the arse to build and fix when something goes wrong because they are so densely packed.
Now, some of this has a lot to do with my own personal situation, I have arthritis in my fingers and only have about 75% use of some of my fingers and these boards are backed dense. Might be ok if you are perfect dexterity in your hands, but if not, well the build is not impossible, just frustrating. It would be nice to have say 30% more board space on all their kits. It would really make things much easier to work on, for me at least.
Anyway, it works, with 12v, 250ma bias and 15dbm drive I am seeing about 5W out, not 10. To get 10W out i need to drive it into hard clip with 1W input and turn the output into a square wave. Obviously not good. I figure it could probably do with some more bias current. Gain is pretty flat which is a nice thing. I will have to come back to this and play further at some point.
What i might end up doing is copying the design and laying out my own board and having some boards made up using larger ferrites, even if I lose some gain at 28mhz, it would be worth it to me as I dont use 10m anyway. If i do this, i will not be releasing my gerbers, because you know that someone will take them and start selling boards and that would not be good.
Power amps are pretty much smoke and mirrors, magic and voodoo all rolled into one for me. I have avoided doing power amps for quite sometime because I find them frustrating Well, i have made some progress, I am now making 5W out of an amp designed to make 10w LOL. I still got some work to do.
So I am sitting here this morning drinking a massive cup of espresso coffee and thought i really should post up where I am at with the receiver project. Its getting closer now to final testing and making noise. In fact, the final board will arrive today from china and as long as it does what its meant to, i might only be days away from hearing beeps
So anyway, onto the IF amps and mixers. I find the whole amp design, input and output impedance matching and how one can effect the other to be slightly confusing. So I went with an IF amp design that eliminated that confusion for me, the TIA amps. Termination Insensitive Amplifier by Wes Hayward
The mixers will be ADE-1 Mini Circuits jobs as I have a bunch of them here doing nothing and figured why not. I do have a board here I am designing with a number of different mixer topologies on it that I will eventually have made and test out homebrew mixer designs more fully, but for now I will use the commercial product.
I built the 2nd IF amp first, so I can have a direct conversion receiver happening in short order once I have a working audio board.
Well it works as designed and does the business obviously. There is a missing trace on the board, so I will eventually have to respin them and I want to fix the layout somewhat also and change the transistor footprints to wide not narrow. I do not like those small pads to solder to. LOL
A couple of months back I bought a pair of cheap lab power supplies off ebay that turned out to be crap. 20mv quoted ripple was closer to 200mv. I managed to clean one up with some massive filtering, but it was impractical and still the ripple and switch noise was to high. So while searching for something else i came across these on ebay. 28v, 10A and a linear supply. They weight about 8Kg each. So did some googeling to see if there are any issue and there is one, over shoot when you cycle the power on and off and there is an easy fix to that by adding a cap. But hey, who cycles power supplies on and off anyway. So i grabbed one and then checked the ripple, about 10mv. Thats perfect, so grabbed another one, cause you just cannot have enough power supplies.
So it looks like I am becoming a HeeHaa fan boy. 2 power supplies and soldering and reword station. Oh the humanity LOL
I updated the board and so its a bit better laid out than previously and have shortened the rf path by moving the SMA connectors Gerber files for the board can be downloaded from here: http://robs-blog.net/Files/Dual_Xtal.zip
I am going to redesign this board. The layout is sub-optimal. But for now, I am going to assemble it and see if I can make 2 filters worthy of use.
The one thing that has always frustrated me with many SSB/CW homebrew rigs is that you get one filter and one filter only. I have seen some use varactor diodes to solve this problem, by varying a voltage on the diodes you can vary the capacitance and this the width of the filter. I thought about going down that route myself for a while, but in the end, settled on having 2 filters as I have lots of relays already.
The plan is for an SSB filter that is about 2200hz wide and a CW filter about 500hz wide. I am also using the good crystals for these also. 4.91520Mhz xtals sorted to within 10hz of each other.
Each crystal was loaded up into my you beaute xtal tester and the frequency measured to within an inch of its life.
My function gen also has a frequency counter that counts down to 1hz resolution. So I measured my crystals and sorted them into piles within 10hz of each other. If i cannot make acceptable filters with such tightly grouped crystals, then there is no hope in hell i can ever make a good filter ;
Out of this pile of crystals I have 6 groups of 8 crystals all within 10hz of each other and a few more groups all within 20hz of each other. Buying these crystals was certainly well worth it. The pile in the bottom right corner are the outliers. It seems even good quality crystals have some in each batch that should be rejected.
Got the parts all sorted, just gotta build it now. Will update this post once i have built and tested each filter.
Part 2: Well i kind of expected that to not take forever, but anyway here is the update.
The build is pretty straightforward and all went to plan
Other than the width being a little wide in both cases and a bit to much ripple, I will say that I am happy with the shape of both filters. I can narrow both up easy enough, just need to change the cap values and the ripple, well it might be a bit of work, I will need to play with transformer values. I used 4:1 impedance transform, but 3:1 might actually be closer to the mark. I will have to play there and see what i can come up with, but a better match will remove some of that ripple.
For now though, I can keep on building the rest of the project as these will be acceptable to get things working. I can make them perfect later. Next job is IF Amps and mixers.