Been a while since i have made an actual qso of sorts, so i did a little FT8 made 6 contacts and turned it all off again LOL Bands are hopeless for anyone running low power and crappy antenna.
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 😉
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.
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.
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.
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.
I have been sitting here today working on the PCB for the WSPR amp and got to thinking about cooling for these transistors. Sure they run cool enough to touch, but im sure over time things are going to warm up some so I threw in a million vias around the transistor and though the source pad to wick the heat away. Then i can bolt this direct to some kind of heatsink and have more than good enough cooling to let her run for forever.
I have got a few boards here almost ready to send off for production. A new BPF board using shielded can inductors. an updated LPF board using SMD caps, an experimental audio filter board where I designed the CW and SSB filters, while I like the hypermite/SSBmite filters I probably cannot really in good conscience release my gerbers as they are a product sold by 4state qrp, so if these work, I can then release my gerbers. Finally I have this test board for the WSPR amp and another PA board for 2m/70cm to send for testing. So much happening at Rob’s Lab its not funny. 🙂
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.
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.