Reading up on the Tuna Topper and funding for amateur radio projects

Since we're now blowing FETs on Project TouCans, and KO6BTY and I are giving a presentation about the rig to the San Francisco Amateur Radio Club on Friday, I've been reading up on amplifier theory. I really like this article explaining how the different classes of amplifiers work except for the horribly gendered  first paragraph.

In other reading news, (it's finals week for KO6BTY and I'm getting ready for our camping trip, so mostly all I've had time to do over the last few days is read), Simon Willison pointed out that the Amateur Radio Digital Communications group has grants for advancing the usage and technology of amateur radio. Here are some examples of what's been funded.

And finally, here's a link to the article that taught me how to increase power output on the Tuna Topper by upping the bias voltage. It's an even more cool article now that I know how the calls A Tuna Topper amplifier actually works.

To wrap things up, we're hoping to get TouCans back up and running today. Here's a nighttime look at the rig from the ground. The white object is the 10 meter rig's balun.

Or, how I learned to miss hard resetting RFI.

Up until about a week and a half ago, Project TouCans and the Flying Rockmite before it had never blown a final amplifier transistor. Our good fortune with transistors was caused in large part not by any particular genius in the construction or handling of the radio, but almost entirely to radio frequency interference. When too much RF energy was reflected back into the radio on key down, the Rockmite's picokeyer would reset chirping out an only slightly irritated 73 in Morse code. Hence, we couldn't use the rig, hence we changed the antenna or repaired the rig, or turned down the bias voltage on the Tuna Topper final until we could use the rig without resetting that little keyer.

Then! Then we did something that was both cool and, (we'd later find out), somewhat daunting. We removed the last of the wires that attached Project TouCans to the Earth and our RFI just went away. Which has been great for signal quality, and as it tuns out it's occasionally been hell on the amplifier.

At present count, we're three transistors down.

After the rig dropped from about 15 feet up to the ground recently, I did a quick inspection and then, (why!!!!??? why did I do that???), decided I'd measure the rig's output power since I hadn't done that in a while. The power meter reported 3 Watts. The rig nominally outputs 5 Watts. I adjusted the bias voltage on the Tuna Topper and.. still 3 Watts. I increased the voltage two more times, and? The final transistor blew out. (Eventually taking the rechargeable battery with it.) KO6BTY and I completed our debug yesterday, reattached the power meter, (which apparently no longer works since it reported 0 Watts at all bias voltages), and fairly quickly blew out the amp transistor again as I blithely upped the bias voltage.

Turns out I can't do that anymore. our keyer RFI safeguard is gone.

Interestingly, we did discover that when the bias is set to low on the amp, there's a whistling feedback tone that appears in the audio output. When the amp is biased correctly, and before it's biased too high and takes out the transistor, (i.e. in nominal operating mode), the whistling tone goes away. Audio debug lives on to a certain extent.

We'll be dropping in transistor number four tomorrow. I'll keep you posted.