W4YWA's Homebrew Rig on 20 Meters

 

Ed W4YWA is far too modest -- he has built a very FB homewbrew transmitter.  Congratulations Ed.  I think your original plan to use a Web SDR receiver will work, if you and the other station are just willing to pause for an additional second or two to let the internet catch up with the real world.  Also, you might find some Web SDRs that have less latency than other.  You could used a little SW receiver or a simple buzzer for your sidetone ( I think sidetone is your most pressing latency concern.)   My suggestion is to try to get a few contacts using the Web SDR (perhaps via schedule -- try the DX Summit or the SKCC web page to set some up). Then build yourself a simple Direct Conversion receiver to use with this rig.  You don't have to try to build a VFO at 14 MHz (that can be difficult) -- you could build one at 7 MHz (use the circuit from our High School receiver project) and pair it up with a "Subharmonic Mixer" so that you can tune the 20 meter band.  Please keep us posted on your progress. 

Ed writes: 

Home-Brew Fun and Failures 

I’m not much of an amateur radio operator, but I enjoy the electronics, self leaning, and the home brewing aspects of our hobby. Here’s an account of a recent effort. While trying to re-learn CW, I discovered web-based SDR sites with waterfall displays, all kinds of filtering and better performance than any of my vintage station receivers. So, I start thinking….. if I had a little transmitter and a simple antenna, along with internet access, I’d have a capable station to take on vacations to the beach. Yes I know, there are web based amateur radio stations, but remember the operative words here are: “Home Brew.” After pinging the Google machine, I came up with a two-stage 1-1/2 watt transmitter sometimes refereed to as the “Universal QRP transmitter,” or the “Little Joe Transmitter.” There’s lots of variations of this circuit but it is essentially a Colpits crystal oscillator coupled to a class-C PA. I chose 20 meters because I didn’t want to hire an arborist to string my antenna. My design modifications included a transistor switch that keys both the oscillator and PA, a VXO circuit, power transistor protection, and a 5-th order Chebychev low pass filter.

Notice the (do I dare say, good looking?) enclosure. In a former life, it was a SD card reader from a defunct PC. FYI, gutted CD/DVR drive cases also make fine enclosures for your home brew projects. I opted for a “foil side up – without holes” for my PCB design. All the parts are soldered down on the lands - no PCB holes. I wanted to change parts without having to do open heart surgery. Functional placement was also important to me. I took more time than I’d like to admit to organize the circuit layout as I did, but I’m glad I did.

When all was said and done, it was time to power it up and….. and …. nothing! Not a single function worked! I won’t bore you with the debug stories that took forever, but the only part I didn’t have in my junk box was the PA transistor. I got 10 of them for $5 off the Internets and they all failed to deliver. I could only get a few tenths of a watt from my design. In a fit of desperation, I un-soldered a PA transistor from an old CB radio and it immediately gave me 1.8 watts of pure CW ! ! ! ! Happy dance, happy dance! But, save your accolades. There were lots of other problems; they were my problems not component issues. For example, before you design your own RF filter be sure you understand cutoff frequencies. They are not the same for every filter design. I suggest Paul Harden’s NA5N site to learn about PA output filters. My first few filter attempts had the transmit frequency well down on the attenuation curve. I was attenuating my own signal ! So, after weeks of “why don’t the damn thing work,” I got a clean signal. Whoo-Hoo!

Now it was time to unshackle the dummy load and see where I can be heard. And, Oh boy… I’m beaming into Pennsylvania, Georgia and Northern VA, all from an inverted V on a tripod mounted paint stick, held apart with two tent stakes. But then, reality took over. My grandioso plans for using the web-based SDRs as a station receiver (and the side tone oscillator for my transmitter) didn’t account for the latency delays of the SDR software. If you ever listened talk radio and the host says, “Turn your radio off – the delay will make you sound like a ….” you know what I’m talking about. You would think that someone who over thinks everything, would have foreseen this issue before spending countless hours of breathing solder fumes? Humility and eating crow are my better traits. But not to worry, I’m not ready to give up. Stay tuned for more adventures of Home-Brew Fun and Failures. 

73s W4YWA