To add to the PA madness that is going on here at the moment, I decided today to build one of the 2 QRP Labs 10w PA’s kits i have here. At the risk of inflaming all the QRP Labs fan boys out there, i both love and hate their kits.
I love that they are well thought out, designed and tested and bring a level of professionalism to the whole kit process, but, and this is the clincher for me, they are mostly a total pain in the arse to build and fix when something goes wrong because they are so densely packed.
Now, some of this has a lot to do with my own personal situation, I have arthritis in my fingers and only have about 75% use of some of my fingers and these boards are backed dense. Might be ok if you are perfect dexterity in your hands, but if not, well the build is not impossible, just frustrating. It would be nice to have say 30% more board space on all their kits. It would really make things much easier to work on, for me at least.
Anyway, it works, with 12v, 250ma bias and 15dbm drive I am seeing about 5W out, not 10. To get 10W out i need to drive it into hard clip with 1W input and turn the output into a square wave. Obviously not good. I figure it could probably do with some more bias current. Gain is pretty flat which is a nice thing. I will have to come back to this and play further at some point.
What i might end up doing is copying the design and laying out my own board and having some boards made up using larger ferrites, even if I lose some gain at 28mhz, it would be worth it to me as I dont use 10m anyway. If i do this, i will not be releasing my gerbers, because you know that someone will take them and start selling boards and that would not be good.
Let me tell you a story. It was a dark and stormy night and not a creature was stirring, not even a mouse. And yet, in a little lab in the middle of nowhere, somewhere out beyond the back of Burke, a little Aussie VK Ham was trying to get an order in with a PCB manufacturer before China closes down for Chinese New Year.
So in my infinite wisdom I needed to rush a 2nd board onto my order to make it more cost efficient on shipping. I only had one board ready with updates and fixes, and I have been meaning to do a PA board for quite sometime, so i fired up Diptrace and opened up the schematics I was going to use, and got to laying out 2 separate designs published by Ruben VK5FE which can be found here
So anyway, the two designs were slightly different in components and the two fets had different footprints and in my cut and paste zeal while doing the schematic capture, i forgot to change the components on the IRF510 board from RD16HHF to the IRF510 component and footprint.
Whats funny in this whole story is that after I posted the above picture to a friend of mine, I joked that the mechanical design was such that if i had made a bomb the PCB would shield me from the FET shrapnel and i should not lose an eye.
So lucky for me when it came time to smoke test this thing I use current limiting power supplies and had set the current limit to 2amps, because when the drain and source pins are swapped on the IRF510 you have made a heater as it will draw infinite current until the wires coming from the PSU overheat, catch fire and burn your house down.
So my board looks pretty but does not work. The other board designed for using RD16HHF1 fets should work a treat assuming I have not screwed anything up there 🙂 But before i go and build one of those, i will be checking it over 3 times as I do not want to waste expensive fets for nothing. When IRF510’s costs pennies and the RD16 costs pounds, you dont want to be exploding things to often LOL.
Anyway, the moral of the story is don’t rush. Check things many times and cont use cut and paste when putting 2 similar designs on the one board. Now i just have to wait a couple of weeks for China to re-open for business and send off the board files I have sitting here now just waiting.
So I am sitting here this morning drinking a massive cup of espresso coffee and thought i really should post up where I am at with the receiver project. Its getting closer now to final testing and making noise. In fact, the final board will arrive today from china and as long as it does what its meant to, i might only be days away from hearing beeps
So anyway, onto the IF amps and mixers. I find the whole amp design, input and output impedance matching and how one can effect the other to be slightly confusing. So I went with an IF amp design that eliminated that confusion for me, the TIA amps. Termination Insensitive Amplifier by Wes Hayward
The mixers will be ADE-1 Mini Circuits jobs as I have a bunch of them here doing nothing and figured why not. I do have a board here I am designing with a number of different mixer topologies on it that I will eventually have made and test out homebrew mixer designs more fully, but for now I will use the commercial product.
I built the 2nd IF amp first, so I can have a direct conversion receiver happening in short order once I have a working audio board.
Well it works as designed and does the business obviously. There is a missing trace on the board, so I will eventually have to respin them and I want to fix the layout somewhat also and change the transistor footprints to wide not narrow. I do not like those small pads to solder to. LOL
So last nights adventure was actually quite profitable. 3 new DXCC entities worked and 2 confirmed already. There was a pretty good opening to Central America and I worked Aruba, Suriname and Belize. Belize was on CW to. I was surprised to see that I had confirms already on 2 of those after I uploaded my log to LOTW. This brings be to 90 confirmed. Ticking closer and closer to that DXCC 100 LOL
There are some little things in life where you want to go the extra mile and have something that is very nice. Coffee is one of those thing. Why drink dirty dish water when you can have an espresso. We got all excited here the other day and went out and bough a coffee machine. Not the most expensive machine out there, but a compact one what would fit on the limited space on the kitchen bench. But the proof is in the drinking and yeah the coffee it makes is nice.
A couple of months back I bought a pair of cheap lab power supplies off ebay that turned out to be crap. 20mv quoted ripple was closer to 200mv. I managed to clean one up with some massive filtering, but it was impractical and still the ripple and switch noise was to high.
So while searching for something else i came across these on ebay. 28v, 10A and a linear supply. They weight about 8Kg each. So did some googeling to see if there are any issue and there is one, over shoot when you cycle the power on and off and there is an easy fix to that by adding a cap. But hey, who cycles power supplies on and off anyway.
So i grabbed one and then checked the ripple, about 10mv. Thats perfect, so grabbed another one, cause you just cannot have enough power supplies.
So it looks like I am becoming a HeeHaa fan boy. 2 power supplies and soldering and reword station. Oh the humanity LOL
I updated the board and so its a bit better laid out than previously and have shortened the rf path by moving the SMA connectors
Gerber files for the board can be downloaded from here: