Antenna Tuner Details and Files

Ok first off, there is no full schematic for this board, I have already moved on to adding new stuff to it and changing how some parts of it work so I can add in new features. So the best i can offer is this extract that shows where the pins on the micro go to.

Secondly, I wont be releasing my code, the reason is that I do not program using the Arduino IDE and teaching everyone how to program in GCC, to install all the tools required, and uploading the code using an external programmer is beyond my ability to teach anyone let alone everyone. There are just to many things that can and will go wrong and it will only make my life miserable trying to help everyone.

That said, the ESP32 can be programmed in Arduino and the actual basic code is not that hard to write yourself. Turn a encoder and it steps through the relay combinations.

With these relays, I would not put much more than 50w though them. Though the data sheet says they will take 1A but that makes them marginal at 100w. As it stands I think 50w is a very safe bet.

Components:
Relays: Omron G5V-1 5V subminiture.
Transistors: PDTC114ET pre-biased SOT23
Caps: 1206 or 1210 Ceramic Multi-layer 1Kv or higher rated, for tuner, 50V 100nF for bypassing. 1uF across the coils of the relays.
Voltage Regulators: 5V and 3.3V 1117 variants SOT223 package.
Toriods: T68-2 T50 would be suitable also, its just what I had, 2,4,8,12,20, 24 and lots of turns.

Schematic as best as i can show without causing confusion because of changes i have made to it. Yeah sorry about that.

Top side of the board as 3d rendered.

Bottom side of the board, 3d rendered.

The board as built by me.

DOWNLOAD: auto antenna tuner_gerber

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The Filter That Never Was

One upon a time in a land far far away, LOL. Well, this is one of those stories and it reads like a horror story. I have spent all day on this, pulling my hair out and trouble shooting and wondering what the fuck is going on here. Is it me, was it my design, was elsie screwing me with stupid values. Well, hold onto your hat Batman, this is going to be a bumpy ride 🙂

It all starts here. Designing a filter in elsie. Bandpass filter, 7.150mhz center frequency, 400khz bandwidth, chebychev response with 0.001 ripple. All good, simple even. I do not like the inductor values it spits out, i rescale the network to use 500nH. And begin to wind up the coil forms.

Everything goes to plan, i wind up 9 500nH coil forms, LCR meter says I am a genius and I agree with it, not only am i super smart and know everything, I am also good looking and a legend. 😉 That was this morning. Now let me rewind things back 4 weeks ago when this plan started to evolve. This should not be the problem.

After having elsie tell me what to do, I laid out this schematic in Diptrace and proceeded to produce a pcb to use. Schematic looks fine to me, looks the same as what elsie says i should do. This should not be the problem.

This is a small screen shot of the PCB layout, if you close your eyes and squint you can see the series capacitance and the shut capacitance and the inductance are all in the right places electrically. This should not be the problem.

Elsie gave this plot as an idea of what the filter should look like. Looks fine.

Never to take the word of a machine seriously, I checked the design in LTspice, just for sanity sake. Looks fine.

Then i built the filter, just one mind you, there are 4 on the board, but i have learned the lesson many time not to jump ahead of myself, because as the Mythbusters would say, failure is always an option. Becides, things going to shit are the norm around here. Today was no exception, bloody abortion of a filter was on 14mhz. Its like 1/2 my inductance and capacitance just vanished into thin air and left me with a pile of shit. And i had no idea why.

Being the clever idiot that I am, i did say i am a legend right, I began by melting the plastic cases on the relays, I mean pulling all the caps off the board and measuring them. Frequency went up, so that means less capacitance and less inductance. I am the boss of making strays of everything on my boards, so i usually have more than i need. Caps turned out to be correct.

So i rechecked the value of the inductors.  Actually i wound the slugs all the way in and as expected the frequency shifted lower. LCR meter says that i had 600nH. More than i needed but I was still on 14mhz, not 7.

Then after much wailing and gnashing of teeth, I grabbed out an inductor of a known value and measured it. It was wrong. Not just a little bit wrong, but a lot bloody wrong. I calibrated the LCR meter and checked the known value again and BOOM right on value. Checked the other coils i wound and they were 160nH not 500. Well there is your problem. I screwed up royally. I did not calibrate my crap and thus made a huge pile of it and wasted half a day on what should have been a 3 hour tour, a 3 hour tour.

So there you have it. That has been my day, fun, entertaining and well, i learned a valuable lesson. Never trust your meter not to lie to you. And with that, i am off to have a shower and cook dinner. The filter board can wait now for another day. I am done 🙂

Oh one last picture, i put some 500nH crappy inductors in the circuit and yeah its in band. Now i need to rewind my nice coil forms and make some filters that do not suck as bad as this nano vna plot looks.

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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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More Receiver Work

So with the VFO and Audio board working i turn my attention back to working on the receiver. Now the first version of this was an unmitigated disaster. Clever me, always throwing caution to the wind used MMIC gain blocks for IF amps and had nothing but trouble with them oscillating and going bonkers. Well, this time I threw caution to the wind again and used high speed op-amps for the RF and IF amps. Everyone has done a 2n3904 IF amp and i could have done the same, but, lets try something different. And i could not be more pleased. Actually using op-amps might just become my thing LOL they are actually surprisingly easy to work with once you know what you are doing.

 

I have posted about this before somewhere on the blog, but this is the circuit I used after reading some app notes from one of the big manufactures. Non inverting, 50 ohms in and out impedance and thats about it really. Unity gain bandwidth of the op-amps i used is 380MHz and they are a 20 cent Chinese part.

Doing the initial alignment of VFO and BFO frequencies I had more probes up its cackler than an abductee at a aliens convention.

 

The mighty RF Explorer spec-an for the win getting the VFO frequency mixing with the RF input to be right smack center in the passband of the 500hz wide IF filter. Yeah its a CW rig this one.

VFO A is the IF frequency and VFO B is the BFO frequency.

And this is the 600hz tone out the AF port. Which will eventually get routed the audio amp that I actually short circuited while fixing it until it was broken. Actually, the AGC and the Audio filter circuits work just fine, its the AF amp i killed. Its just a matter of de-soldering the amp module and replacing it with one that works. Every day I am getting closer and closer to something that actually works good enough to use more than once.

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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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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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Measuring Gain Bandwidth With NanoVNA

The NanoVNA is more than just a fancy SWR meter for checking your antenna. Its much more and a very useful tool for the home brewer building amps and filters and the like. Now i have been buying things like crazy for various projects that I would like to build in the future. Often these parts are spec’ed for bands not of interest to me. So what do you do? Well you measure them at the frequency of interest and see how they work yourself.

Below is a MMIC amplifier part that I found for really cheap. By cheap I am talking in the 40 cents per range, so i bought 100 of them. I mean why not, they are spec’ed for 100mhz to 3gig with +30db of gain. Worst case senario they are kind of useless at HF and I will have parts for when I actually want to build things at VHF and up.

So anyway I had a test board built with 4 different circuits on it for testing out various parts I have here and it includes Op Amp, Mosfet and BJT amp circuits. So i decided to start with the MMIC and see what it can do.

The good thing about MMIC gain blocks is the fact that they have such a low parts count. 2 blocking caps an inductor, bypass cap and gain setting resistor. Initially i set the bias resistor a little to high and was getting a lot of distortion, so I halved the value and boom it was providing 24dB of gain at 7MHz, which is my go to frequency for all these sorts of tests. Next though, I wanted to see how the gain bandwidth was. My bandwidth of interest is HF so 3 to 30MHz, so just for shits and giggles I measures it out to the 6m band.

The test setup was Port 1 of the NanoVNA to the input of the test board, the output of the test board to the RF Sampler i made the other day, which was also connected to a dummyload and then back to Port 2 of the VNA. Then an sweep of was performed and the S21 Gain was measured.

Things actually looked quite nice and rather flat. A few dB down at 80m and 1 dB down at 6m. That is pretty good for a part with a minimum frequency of 100MHz. So all in all, this part is a winner and something I can use in a project sometime soon.

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