I’ve decided to build a BITX 40. This petite SSB transceiver sells for a mere $59, some assembly required. As it comes, it puts out approx. 7W, and with some straightforward upgrades it can produce 25W. It comes as a fully-assembled PCB plus most of the parts needed to hook it up. A case, speaker, and a few other incidentals are not included. The board and radio are designed to invite hacking and customization. It is also designed to serve as an introduction to homebrewing for hams who may not be ready to build a radio from scratch. For more information on the BITX-40, see its supplier http://www.hfsigs.com/ and the active and helpful support community at groups.io.
My BITX 40 is operable “al fresco” on my workbench. The included Arduino/Si5351 VFO works fine and tunes the full 40m band. It needs a little bit of work before I can transmit with it. It’s important to understand that the BITX 40 is not a turnkey rig. Many of them ship with small flaws, and figuring out and fixing the flaws is part of the fun. (This is why that helpful community at groups.io is so important.) Mine shares a flaw with Wayne, N6BM’s BITX 40 — the BFO frequency is inside the IF passband, instead of about 300 Hz below the passband like it should. This means that stations I tune sound bassy, I can hear part of the opposite sideband, and when I transmit, the carrier is not suppressed.
(I suppose I could call it “vestigial sideband”, like what NTSC TV uses, but it’s supposed to be SSB…)
Wayne fixed the problem by changing a capacitor in the BFO circuit to pull the frequency where it needed to be. I plan to fix it by disabling the analog BFO and instead use a spare Si5351 output. Having a tunable VFO will let me put the passband exactly where I want. With a little more code, it will also give me passband tuning.
I think I found a bug in the microphone amp that I’m going to take a closer look at, and I found a perfect case at the Mike and Key hamfest in Puyallup last month. I didn’t even try to negotiate the price. It was free!
I’ll have more on my BITX 40 project in upcoming posts.