It Did Not Work


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.


Yet Another 5w Amp

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.


I Now WSPR On 3 Bands

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.


Tri-band WSPR Transmitter

3 posts in 1 day. HAHAHA. Got this little amp working. Its making less power than I expected, or would have hoped for, but 3 watts is handy, was expecting closer to 5. Anyway, when dialed in, it will only be running 1w on 20, 15 and 10m and will run 24/7 while the antenna is not needed for anything else. 🙂


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.


A Tale Of 4 Broken Fets

It was the best of times, it was the worst of times, so is the winter of discontent, hay fever and corona virus. Today i have been playing with this amp board i designed a whole ago and have had sitting here until i could be interested enough to actually drag it out and populate it. And today that is exactly what i did.

Nothing revolutionary here, its IRF510’s in a 2×2 push pull configuration. VCC = 24v, Drive = 5W there is some negative feedback and all the usual goodies. So with everything connected up, i turned down the current limit on the power supply just to be sure to be sure, turned on the supply and slowly began to increase the current.

The scope was saying 40v rms and I think to myself that is about 35W. I should be doing more than that with the amount of drive and current being drawn, but I left the PSU in current limited and i was playing it safe. I look at the Swarez meter and its showing 35W.
So i open the taps and give her all the current she has got. I look at the scope 200V p-p thats 100W and the Swarez meter only showing 35W. 3 minutes later BOOM all the fets let go. Checked the Swarez meter, it was in the 2Kw range, not 200W range, I was doing 100W and the heatsinks on both the amp and the dummyload were toasty warm.
So, to much bias, to much drive and ultimately to much current. But I should be able to turn this down to a nice 50W and it will kick along without much drama.

The End.


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.


WSPR Amp Prototype

So i have been thinking about an amp to use for WSPR. I have so many parts here and so many options its not funny. What I am thinking at this point is to use these UHF fets I have. Specs in the datasheet says they should be good for 18db of gain to a max of 7W. What I am thinking of doing is SI5351 -> Single -> Push Pull. This should get me to a couple of watts or there abouts.


Last time that i built this circuit up i burned the pads off the PC when i ran way to much current though it. In the datasheet, 200ma is not the amount of bias, its the amount of total current. Actual bias is only 1/2 a bees dick at most. Less than 2V and that changes depending on what VCC is being used.

200mW drive yields 1.2W out. VCC is 7V and total drain current is 400mA.

I had to break out this bad boy because the ammeter in the HooHaa power supply is about as useless as tits on a bull. When it displays 0.1A you are pulling more than 1/2 and amp and the board starts to smoke.


Low Pass Filters for WSPR TX

In among taking naps and blowing my nose (yeah i got hay fever or the flu) today, I wound the toriods and built the low pass filters for the WSPR transmitter. I can now connect it to the micro and make it multibanded. The filters are not my best work ever, but I will suck up the 3db losses and just use them. I think i will respin the board using SMD caps, as I have better quality caps in SMD rather than these crappy ebay multi-layer ceramics that are really not much good at all.



A couple of weeks back I was toying with the idea of using the board i developed to use in a transceiver and programming the ESP32 to do WSPR. Initially i tried connecting the ESP32 to my home wifi to lookup the time from an NSP server etc etc but I had trouble with the ESP32 not connecting to my wifi.

After enabling better debug messages and doing some google foo searching for the answer, i took a good look at the debug messages and discovered that the brownout timer was being triggered because the voltage on the USB ports on the front of my machine was to low for it to be happy. Changed the cable and changed to a rear port and I was back in business.

Half an hour later i was watching wspr coming out of the SI5351a on the oscilloscope and i knew I was in business. Grabbed out a small PA and LPF, connected it all together and we were in business.

Power out of the PA going to my antenna is about 1W. Since I took the screen cap below, i have upped the voltage going to the PA to bring the output up to exactly 1W.


And as for whispering, we are whispering sweet nothings to all the usual suspects. I do not expect this to break any land speed records, but its been a fun exercise and now I am going to work on adding switchable LPF’s and ramping this up to 4 bands. I have 2 antenna here, one is a 40m dipole and the other is a tri-band trapped vertical. So having 4 bands running should be cake. I do have the boards for the LPF as well, i just gotta build them and code up the band switching.