Round and round we go, where we stop, everybody knows. 27 turns. HAHA
I dont remember ordering these transistors, but they are cheap, i have 100 of them and so i mounted one up on a test fixture to see what it could do. To my delight, I was seeing 1.5w out and I am thinking I hit the jackpot. I can push pull these as a predriver stage and its not going to cost much for a good amount of power.
A couple hours later, I noticed the scope probe was on 1x and the scope on 10x. My super awesome power just vanished out the window. Its still a good transistor, reasonable gain for small signal stuff, good enough bandwidth to be useful for most the HF bands of interest. Its just now a power house HAHA.
Oh well. It is what it is 🙂
I am building something where I needed some IO expanders. I have these modules sitting in my box of arduino crap and figured i could desolder the headers and reverse them and then plug these into my pcb board.
I got to starting on that when I realised, there is no annular ring on the top side of the board. There is no way to really solder the headers in the other way. Bloody stupid board designers doing stupid things like this.
Now to find a solution to my problem.
So I pulled everything off the shelf to give this a test. Its working. What I have done in the pictures below was to use an DDS vfo as the incoming 7mhz signal. It run into as much attentuator as I have here, giving a final signal out of about -95dbm or there abouts according to the spec-an. This number is rather uncertain because that is right on the noise floor of the device and by my calculations, the actual signal is closer to -100dbm. Now I am still hearing a signal out of the speaker at that level. So its not an Icom, but its not totally deaf either. I do think i could use a little more gain in the audio stages. But, we will see how things pan out with some loudish signals on 40m this afternoon.
For whatever reason, the MMIC amps in the receiver are super unstable. They have 2 states, oscillating wildly or not working at all. This is a real head scratcher, because the exact same circuit using though hole parts was super stable. The other thing is, if i stick my finger on the input cable, it becomes stable again. Go figure.
OK I got it sorted out and now its stable. The issue was the limiting resistor R9 was to low a value. I am not sure why the through hole version was happy with 60ohms and the SMD version wanted 150ohms. But, either way, I learned a valuable lesson here with MMICS, if they are going bonkers and oscillating wildly, cut their current back by increasing their limiting resistor.
Its still not working, but it is getting there. All be it, slowly. So i fixed the oscillation in the PA, replaced the fet and now at least the PA is all working as it should be. Now I am still not getting anything out of the Mic. Not sure what is going on there, but there is power and it worked when i bread-boarded it. Obviously something is not right, but I will work that out soon enough.
A few days back I slapped together an superhet, it kind of works, certainly nothing to rave home about that is for sure. A few take outs from it, using MMICs as IF amps is not a clever option as you really cannot control the gain all that easily. And the other thing is audio. You really gotta make sure you use an audio amp with sufficient enough power rating to drive a speaker.
After playing around with things, I did notice that I had some rather obvious distortion. After changing out the audio amp for something sturdier and testing the audio stages by themselves, I came to the conclusion that the distortion was coming from the IF amps. I will see if i can tame the gain in them somewhat and see if i can get this working better.
I am still not sure about the audio sound, the SSB filter is somewhat thin and the audio AGC is really not AGCing. I am not sure what is going on there. But I have an AGC ic here on a board that i might try and see if that works better than the discrete version that I built.
I configured the superhet with both CW and SSB IF filters. Not sure how good my filters really are, but once i sort out the distortion, it should be able to see how the filters perform.
I have a couple of these AD831 mixer boards that I bought off ebay ages ago. Been thinking about building a receiver out of ebay modules just for laughs. So i got them out of the parts trays and fired one up to see if they are even working and functional. Looking at the output on the spec an, it would seem they work plenty fine and are within spec.
So the other day I broke the USB connector off my board. Plenty of ways to fix this, but going forward I am going to start putting programming headers onto the boards I use and plug in an FTDI programmer to do the business. If you take a look at the picture above, you will see how I solved the problem in the short term, just cut a USB cable and wired it directly to the CH340 serial chip.
This is where I ran into trouble 🙂 you would think that red and black would be Vcc and Gnd, but no, this cable is not wired up to the USB standard at all. Red is D-, Black is D+, yellow is Gnd and White is Vcc. I was scratching my head for a while after I first wired it up and it was not working, then proceeded to buzz out each wire with the continuity meter.
Put the correct wires in the correct place and BOOM, i was able to program the micro. More to come on this board soon,