After I killed my homebrew upconverter, I went back to messing around with ads-b and dump1090. The little antenna that came with the rtl-sdr dongle worked okay, but I wanted to build a better antenna to see if I could get more range. I looked online and found quite a few pages on coaxial collinear antennas and I had everything I needed to build one, so I figured I’d give it a shot.

For the next step of my homebrew direct conversion receiver is the audio amp. I used this schematic from N6QW’s Simpleceiver posts. Here is the amp mocked up on a breadboard. It worked, but not very well. There was a lot of noise and static. At this point, I thought about switching over to a LM386 based amp, but I went ahead and soldered it up on a piece of copper clad.

I rebuilt the si5351 vfo on perfboard. I went with an arduino pro mini with the adafruit si5351 breakout board and a 16×2 lcd screen I pulled out of an old printer. I’ll be using this vfo in a direct conversion receiver. You can see the start of the audio amp on the breadboard in the background. In other news, I attempted to finish my upconverter. I built it out on a board and replaced the si5351 with a crystal oscillator and added a few filters and now it doesn’t work.

Over the weekend, I put together a few simple antennas and hung them in my attic. The first was a 20 meter dipole, the second was a planar disk antenna. 20 meter dipole For the dipole, I used 1/2 inch pvc pipe as the insulators and 14 gauge stranded THHN for the elements. First, I cut a few pieces of PVC and drilled holes to feed wire through. For 20 meters, using the formula, Total Length = 486 / Desired Frequency, I ended up with 16.

I picked up one of the cheap ad9850 modules from China and made a new vfo. I modified this code from ak2b to use the ad9850 instead of the si5351. To see my si5351 vfo, click here. As you can see from the waveform and the frequency counter at the bottom, this little module seems very accurate. Since it also produces a square wave output, I may try to build a little function generator.

Being a new ham, I’m starting to find myself in need of a dummy load. I’ve decided to build one of the fairly well-known paint can dummy loads. You can see some examples here, here, and here. The basic construction of the dummy load is twenty 1k ohm metal film resistors in parallel, sunk into an oil filled container for cooling. Using 3 watt resistors, it should be able to take 60 watts easily and with the oil cooling it should be able to handle up to 100 watts for short periods of time.