OpAmpia: The Op-Amp Receiver

They say a picture is worth 1000 words. Well A video must be worth 1000 pictures then. I have to admit, i really do not enjoy making videos for youtube. I do it reluctantly and only when I really have something worth showing off. I really do not care about building an audience and being famous, I just like to do what I want, when I want and not feel compelled to make anyone else happy other than myself. I am not entertainment, I am just a guy who is documenting his journey, nothing more. Even this blog, its not a how to, its not a guide, its often not even correct, does not work or is fundamentally flawed. That is what happens when you home brew. You make mistakes, things do not work and you have to trouble shoot and trouble shooting means learning something. A good day for me, is a day I learn something.

Well, this is the PCB. I have named this receiver OpAmpia. Because its just a bunch of op-amps. There are 3 high speed op-amps on this board, acting as RF Amp and IF Amps and then on the other board another 5 op-amps doing audio agc and preamp and audio filtering. So all up, we have 8 op-amps, hence the name.

This is a revision of what I actually built. I have redesigned the bandpass filter and will be using TOKO styled canned inductors. The higher Q of the inductors should see much less loss than the SMD inductors I used on the test board.

Same goes with the IF strip, the IF filter is now not plugin, but will use all SMD components, I have a bazillion SMD crystals and so its time to start using them. Actually in everything I am moving away from through hole components where I can. SMD is just so easy to use you can always find a useful part that is cheap. Take the Gainsil op-amps I used, they cost like 30 cents each. Try and find a highspeed op-amp in though hole for that price.

For alignment I used the function generator set to 7mhz and with both VFO’s showing no offsets tuned things until they sounded great. Having 2 VFO’s really helps here. Now i can just do some simple math and remove the offest and display the actual RX frequency. A little bit of coding and we will be in business.

That’s all from me. Another month and I might have this as a complete and working transceiver. LOL Who are we kidding 😉

 

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The Fine Art Of Making Power

Make no mistakes, I think real amp designers are witch doctors and that amp design is more voodoo than art. But this has never stopped me from having a go and seeing what I can come up with and what I can learn.

Today I hit a new milestone, I raised peak power to 50W. 50W might not sound like much to those who have gone out and bought their kilowatt to power cheat with, or for the guy who bought a amp pallet off the interwebs and assembled a kit. But for me, someone who has looked at lots of schematics, tried to understand each design decision the designer made and why they made it, then went and captured the schematic, laid out the PCB and had boards made, 50W is something of an achievement.

And don’t get me wrong here, 50W is what WA2EBY was getting out of 2 IRF510 and I am using 4 of them to make that same amount of power and still struggling to contain the magic smoke within the epoxy that is covering the silicon.

I was hoping for a little more out, 70W or there abouts would have been really nice. I do have room to push the amp a lot harder than I currently can. I can give it more drive, more bias and more voltage, with the current limitations being 5w drive from a CW transmitter i home brewed, 2V gate bias, and 30V and 10A from the lab power supply.

Along the way many parts were broken. I call this pile My Shame. Actually its not as bad as it looks, the first 4 fets to go were Ebay specials from China. I think they are fakes, they were never happy and just ran into uncontrolled oscillation.

The next 4 were all my fault. I gave it all the amps and they gave up the ghost after about 40 seconds of full key down madness.

This is the current mess of what is my work bench. Plenty of crap on the bench. A certain old guy home brew legend would say my bench is to clean LOL

Nothing like burned flux to get the soldering fan boys to go wild. There is nothing fundamentally wrong with the board, its is a little bit pedantic though. Its window of oportunity is quite narrow. Its kind of all or nothing. I had to change the input transformer and its ratio, the bifilar inductor feeding power needs to be changed as it gets to hot. Everything else is ok. Mechanically its easy to change out the fets on detonation. That is a plus.


Using the CW transmitter I built a while back to drive it.

This is the schematic. I probably should learn about temperature compensated biasing to make it a little more bullet proof. Other than watching the duty cycle and keeping it to say 50% or less, its ok and I have not harmed anything yet. It really could do with a bigger heatsink and some forced cooling to really crank it up. But for now, I am happy that it works.

I did key it up on 40m and sent some CW with it. Listening on KiwiSDRs i could hear myself in VK2,3 and 4. Not that, that is a challenge, I can do that with 5w. But i know its working and sounds fine. So that’s the end of this journey. I am calling this one won and done and now its on to the next thing.

Better add this image as well. Fiddy Whats. Oh one last thing, 5w in and 50w out, is 10dB gain. It is what it is.

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40m WSPR Transmitter

Following on from playing with WSPR last week, I grabbed out on of CW TX boards i have here, reworked the gain in each stage to account for the greater signal input from the SI5351a and ended up with 8W out. Keydown for the last 30min and all the important bits have remained steady at 55 Deg C. So it should be more than upto the job of high duty cycle TX from WSPR.

The Transmitter board.

Signal from the SI5351A VFO board.

What the scope says is happening into a 50ohm load. And here are a few more pictures, because why not 🙂

Setup as transmitting currently into my 40m antenna.

A close up of the swarez meter. Showing 6W but its closer to 5W according to the scope.

And this was the reports after the very first wspr cycle. It works rather well.

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ESP32 With Dual VFO’s

Hey look, its a home brew radio post. HAHAHA. So i have settled into this whole locked down for corona virus nightmare and have sorted out most things and have a game plan for how life will go on for the next 6 months of lock down and no work. And because i have everything in order, i have slowly been getting the enthusiasm to get into building some of the stuff i have in the pipeline and seeing if it works.

I have shelved the tuner for now, i really am not sure about it and it or how to correct its problems, which are both design and code and have started on the second iteration of the universal control board. First time round all the audio stuff worked just fine, more or less, but there were some design issues in the micro controller side of things. Namely, i screwed up things pretty bad and destroyed the 2 older ESP32 Dev Boards i had here which meant redoing footprints and all the other exciting things.

Obviously not everything has gone smoothly this time either, turns out that i laid out the board with to use an L7833 3.3v regulator as I am using a L7805 5v regulator as well, you know bog standard parts everyone uses. But guess what, the TO220 3.3v regulators I had were 1117A’s and they have a different pinout. Turns out, getting an L7833 regulator in Australia is not as simple as it seems, I had to order them from Element 14 for way to much plus way to much in postage. But, it got the parts and well got to getting this thing working. Lesson learned.

On the board, we have an ESP32 micro controller, the little red daughter board is a shift register module, ESP32 is 3.3v logic and most of the crap hanging off it is 5V logic, thus the need for shift registers on the I2C lines. The fuse is there from another lesson learned from the previous version of this board where I turned the solder on the micro into lava HAHAHA. We also have 2 headers for LCD screens, 2 rotary encoders, SI3531A module, yeah still using modules because the 2 times i have tried to roll my own using bare components, they never worked, and finally a real time clock. There is also footprints for 5 buttons, one of which is a reset button for the micro, 2 banks of 5 pins for band switching and pads for a thermocouple for monitoring heatsink temp of the final PA.

A bit blurry, but this is the initial fire up to make sure that I had things working right. Not much use spending hours writing code if there is an issue on the board.

Here I am starting to make some progress on the software, which is pretty much a ground up rewrite of one of the basic VFO codes out there, I think if i recall right was a very early version of a VFO by Jason Mildrum NT7S https://nt7s.com/

And finally, this is where I am at with this. All the buttons work, the rotary encoders work and both the displays work. The one thing i do not like about just about all the VFO codes out there is that they all follow the radix math method for setting the vfo increment value. I want to have a 500hz increment, and actually, when i start to build things for 2m FM i will want an 12.5Khz increment and the like. Now using radix math you only get to have things go up in orders of magnitude, 1, 10, 100 etc. So I changed how that all works and simplified things alot, by combining the increment and displaying into the one function that gets checks once per loop. I can now set my increments to whatever value I like to suit my purpose.

Finally before i close down this epic post, on Jason Mildrums etherkit github https://github.com/etherkit/Si5351Arduino/issues/66 some people have reported issues with ESP32 and the SI5351A library. I am not having any problems at all here. Everything works as expected and there are no I2C glitches. Well, that was a manuscript, thanks for reading and I will catch you next time.

Rob.

 

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Corona Virus Update

Corona virus, whats it mean to me and my home brewing? That is an interesting question and one i am asking myself daily. Sure it looks like I might have more time on my hands with the chance of being locked down growing daily. So that is the positive. The negative is I am also watching the economy tanking and along with it my income. I am a contractor, our clients are all pulling work so that means I will not be earning much at all. This is ok, I have some savings and will survive, but it means that I will lock down my budget to essentials and so I cannot see me starting any new projects for quite sometime.

However, I do have 4 or 5 projects already going on at various levels of progress, so i have plenty to do for now and I have a lot of parts so that is not going to be an issue. I think what will happen is that once i have worked through the projects in the cue, I will end up going back to doing manhattan builds with through hole parts. I have a lot of board and parts, so I am good for a couple years at least. About all it will really mean is that I wont be buying any fancy PCBs at all.

Oh and I have a lot of kits here also, so I can bring them out when things get desperate and have something to build. All in all, i will be ok, but if things get really tight, I might have to shut down my blog, or move back to cheaper VPS hosting rather than having dedicated server hosting. One stupid flu and the world is turning to shit.

Stay classy everyone.

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What A Dummy :)

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 🙂

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Its Working Again :)

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.

The receiver setup with the attenuators.
DDS VFO used as the signal source.
Function Generator being used as the VFO and BFO.

 

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Open Heart Surgery

 

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.

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