So i was slowly creeping up on giving this all the amps. Moved it from my 10A current limited lab power supplies to the 40A monster I use to run the radios, which has no over current protection at all. This is not normally an issue, when things go from production to daily drive, they get fancy things like input fuse protection to protect the wiring from melt down if something goes dead short.
Now the amp, it works, works really good. With very little gate bias and very little drive, at 13.8V supply, I was getting 50W out and it was not even breaking a sweat or getting hot. So i figured it was time to up the ante and turn the gate bias up, slipped with the multimeter probe and shorted it out and gave it all the amps.
Like Tim the Toolman I gave it 40A of raw power LOL and the main power trace became a fuse and it gave up the ghost. Anyway, 50W is the most stable and usable power I have ever made and this thing will go much higher than that. With the right drive and bias combination i can see 75W+ plus out of it. But even at 50W it will run all day and not break a sweat. And mostly that is what i care about, Having something that will run all day and not be stressed out rather than something making all the watts but on the verge of wanting to take an eye out when a FET explodes.
Next version of the board will be fuse protected. Actually, all the boards I have sitting ready to be send off for manufacture are about to get fuse protection 🙂
I have been thinking about re-configuring my WSPR transmitter and adding a few more bands. I have 2 antenna, a 40m dipole and a triband vertical for 20,15 and 10m. So, the way I see it, i should be able to run WSPR on 5 bands, 80 through 10m with the 80m band being not that great.
I also figured that WSPR is nothing more than CW, so why not use class C amps and gain some efficiency. After a bunch of googling and looking at what parts I have here, i settled on the following push pull design that should cover all the bands I want.
I can fit 2 of these on the same board, and run WSPR on 80/40 and 20/15/10 transmitting on both antenna at the same time. I have a board laid out, its just a matter of sending it off to get make. And before i can do that, i need to finish off a couple of other boards i have in the works.
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.