Don’t you love it when a plan comes together? Well, if you are going to copy the work of a master, you cannot go past copying the work of Wez Hayward. Having built this amp design before on some copper board with through hole parts and done a whole lot of measurements on it, I knew that it was a design that was not going to disappoint. What I was not ready for though, was just how much better it is when using somewhat better design principles, SMD parts and an average PCB layout.
Just how good is it? Well, flat gain from 1Mhz to 50Mhz, without using any fancy transistors, just plain old vanilla popcorn 2n3904’s.
The dip between 5 and 7Mhz is an artifact from the NanoVNA and is not actually there, i looked with the oscilloscope and function generator just to be sure. While the NanoVNA is good, its not perfect, but as AVE likes to tell us, its good enough for the kinds of girls I go out with. The gain, in dB is actually also not right.
The input is 100mV and the output is 1V, by my math that is 20dB gain, so its exactly as designed. All that is left is to populate the attenuators and I have an variable gain amp to use for testing purposes or a receiver front end, which is the ultimate end use for this.
So between the first iteration and the 2nd, I have changed from using Sprint Layout to using Diptrace. I have tried a few different programs from Kicad to the free version of Altium and I just could never get the hang of how to make components and footprints in either of them
Diptrace on the other hand I find to be much more intuative and straight forward to use and I can make components and footprints in it with easy, as will be seen later when i get the latest batched of board back from china and write a blog post. So many new parts all created by me in the one library so i can find all my parts easily.
Anyway, to the board at hand. Its still got a couple of minor mistakes on it, the cap footprints were in 2.54mm not 5mm which the caps I use mostly are, the 5v regulator and caps are in the way of the right angled SMA connector and I am not sure that the variable RF preamp is actually varying. Circuit wise it should work, but the spectrum analyzer was not showing any gain change.
Anyway, the design will not be changing now, its built, tested and it works. And i can stay like that :