L Match With SWR Bridge Cont:

Putting the finishing touches to the antenna tuner project, I just need to cut the shafts down a little and put the knobs on. I have given it a test into 2 dummy loads, a dummy load and my 40m antenna LOL, and the led comes on super bright with 5w going in. All in all I am pleased with the outcome, though i would have preferred it in a smaller case, but the inductors use kind of determined the case it when in.



QRP L Match With SWR Bridge

So with the new year comes new projects, I am not going to set out what my overall plans and goals are as I have started way to many things and never bothered to see them through or to complete them. So with that in mind, I am building a L match

Its hard to make out, but you can just see the LED glowing, the signal is 10v p-p from the signal generator, the load is a decade resistance box. At infinite swr there is 1/2 the p-p voltage at the junction of the rectifier and capacitor. As swr approaches 1:1 the voltage drops to a point where the LED turns off. Its simple and its a winner.

It will get paired up with the sotabeams switched inductor and a 8-370pf air capacitor. as an L match. Should be good enough for the kinds of girls i go out with. Below is the schematic I am following for this project and a link to the authors site is at the bottom of the page. In the final build I will use 3w 50ohm resistors and the diode i used was a Schottky, i don’t recall the numbers it was just something i had in the parts box, I used the Schottky for its lower voltage drop, though that is probably not all that critical seeing that LED’s are current limited, not voltage.

Link to authors blog post: HERE



Sotabeams Switched Inductor

This is an interesting little kit and not much information on the net about its use so I thought that I would add a quick blog entry about what I discovered about it. I am building an L match and started with the inductor. I really had no idea on windings, so i started with 6 turns and added 2 turns per inductor, with the 7th inductor having 18 turns on it. I spent about 20mins working out the switch, it is meant to be a 6 position switch, which in reality is a 10 position switch with a limiter. However in my case, it looks like i was given a 5 position 2 pole switch. While mildly annoying, with 5 positions I get 270nH -> 3.7uH inductance, and if i switch from the low side input to the high side input gives 1.7 -> 5.5uH, while adding switching is a pain in the arse, it is not the end of the world to have one inductor not in the loop. If i had realised before soldering in the switch i would have used a 10 position switch i have here and made it work right from the beginning. It is what it is, no use worrying about it now. 3.7uh is more than enough inductance for any antenna i build.



uBITX Has Arrived

Saturday morning, not usually a day for mail here, but because its christmas the parcel guys are working weekends to make sure they keep up with the volume of mail at this time of year. It also means I have the new uBitx sitting in my hands.


Weather Station

With the arrival of some solar panels and an ADC in the post today, its back to the weather station to getting it fully working by January. I have worked out where its going to live, now i just have to put the door on the front, some bug screen over the vents and paint it white so that it stays as cool as possible in the harsh unforgiving Australian Summer.

The panels apparently put out 1amp each at 5v. Yeah right, but 1 is putting out enough current to turn on the charge circuit and so thats a win. 2 Panels should in theory keep the batteries fully charged in the daytime and run everything, just fine. 2 might even be overkill, but I do not want to run out of battery because its been cold and overcast for 5 days. But hey I think my math is ok and it should survive 5 days without sun.


QRP Labs Phasing Receiver Part 2.

Well i have it all built, now i need to dig out a DDS LO and give her some power and see if it is a skookum choocher or if the pixies turn to smoke and leave the building just like Elvis. I did not enjoy building this all that much, the form factor is tiny and everything is stuffed in there as tight as it can be. But, if all goes well, tonight we might hear something coming out of a speaker.


QRP Labs Phasing Receiver

While QRP Labs makes some wonderful kits, they really could do with adding 20% more board area so that old sausage fingers can got in there and do some Da Finger Poken. I get that some things really need to be packed in tight, but others do not and I think the filter boards can be much bigger and contain a 2nd set of holes for the wires rather than trying to solder them to the tops of the header pins. Anyway that’s enough moaning from me. The kit is going together well  all tests have been successful and I am confident that it will eventually power on and work.

I got reading glasses a few months back, but I can tell you I am really noticing how hard some things are to do, to solder that one smd park i had to use both my glasses and the huge magnifying glass to get the job done 🙂

I love it when a plan comes together, needed 3.1uh on the 2 inductors, and guess what I got, 3.1uh HAHAHA.


I still have the polyphase board to build. Then i need to start working out what bits i am going to add to it to make it complete. Arduino and SI5351A obviously and some kind of AF amp should do the trick. More on this to come.


TDA2822 Audio Amp

So I have had this pile of Ebay sitting on my desk for sometime and today I have gotten excited enough to actually start taking a look at it all and seeing how it works. I got these frequency generator chips for like a buck and after setting them up with the test circuit, i could not get them to work, it happens, now and again you get Ebay’d in the butt.

So I figured next i should test out the TDA2822 audio amps. I for 50 for 2 bucks which is a lifetimes supply. Do they work, well, yes they do and here are the results.

Here is the test circuit straight out of the PDF. As you can see parts count is low. So I put the IC on the breadboard and used just 1 1/2 for a mono amp. I also used just 2 caps, pin8 to ground, 470uf as it was already on the breadboard and the input cap on pin 1. Powered with 8v as its a handy voltage i have on my breadboard. 12v would probably be a better option to allow for a larger voltage swing.

As you can see, nothing fancy here, just the IC and 2 caps and my signal gen and oscilloscope probes doing there thing allowing the pixies to in and out and display them in the screen.

So we stick in 0.1v 600hz sinewave and see what happens.

Well, we actually hit the voltage rails and clip somewhat. 0.1v in almost 8v out, that is the voltage gain there. And when i do some da finger poken, the IC itself is cool to the touch, not warm, not hot, but about the same as ambient temperature of the room. So i am thinking Bye Bye LM386, and hello life time supply of TDA2822. And being a stereo IC, I can also bridge the left and right for even greater output. Not that I think i would need it.