23 | August | 2024 | Hackaday

You might think that TV stations or production houses would be great at archiving, but it’s not always the case. Particularly from the public access perspective. However, if you’re a fan of The Famous Computer Cafe, you’re in luck! The beloved series has now been preserved on The Internet Archive!

If you’re not familiar with the show, it was a radio program broadcast from 1983 to 1986. It was pumped out of a variety of radio stations in southern and central California in the period. The creators making sure to keep a copy of each episode in reel-to-reel tape format. For years, these tapes were tragically lost, until archivist [Kay Savetz] was able to recover some of them from a recent property sale. From there, a GoFundMe paid for digitization, and the show has been placed on The Internet Archive with the blessings of the original creators.

This is quite the cultural victory, particularly when you observe the list of guests on the show. Timothy Leary, Bill Gates, Jack Tramiel, and even Douglas Adams made appearances in the recovered recordings. Sadly, though, not all the tapes have been recovered. Episodes with Gene Roddenberry, Robert Moog, and Ray Bradbury are still lost to time.

If you fancy a listen, 53 episodes presently exist on the archive. Take a trip back in time and hear from some technological visionaries—and futurists—speaking their minds at the very beginning of the microcomputer era! If you find any particularly salient gems, don’t hesitate to drop them on the tip line.

[Hans Rosenberg] knows a thing or two about RF PCB design and has provided a ~~three-part~~ four-part video demonstration of some solid rules of thumb. We will cover the first part here and leave the other two for the more interested readers!

The design process begins with a schematic diagram, assuming ideal conductors. Advanced software tools can extract the resistive, inductive, and capacitive elements of the physical wiring to create a parasitic model that can be compared to the desired schematic. The RF designer’s task is to optimize the layout to minimize differences and achieve the best performance to meet the design goals. However, what do you do when you don’t have access to such software?

[Hans] explains that at low frequencies, return current flows through all paths, with the lowest resistance path taking most of the current. At higher frequencies, the lowest inductance path carries all the current. In real designs, a ground plane is used instead of an explicit return trace for the lowest possible impedance.

You really wouldn’t design an RF circuit like this.

[Hans] shows the effect of interrupting the signal return path on a physical test PCB. The result is pretty bad, with the current forced to detour around the hole in the ground plane. A nanoVNA shows a -20 dB drop at 4 GHz, where the ground plane has effectively become an antenna. Energy will be radiated out, causing signal loss, but worse, it will create an EMC hazard with an unintended transmission.

Additionally, this creates an EMC susceptibility, making the situation worse. Placing a solder blob to bridge the gap directly under the signal trace is all that’s required to make it a continuous straight path again, and the performance is restored.

Floating planes are also an issue in RF designs, causing signal resonance and losses. One solution is to pull back the planes near the signal or stitch them to the ground plane with vias placed closely on either side of the signal trace. However, such stitching may slightly affect transmission line impedance and require tweaking the design a little. The next two parts of the series expand on this, hammering home the importance of good ground plane design. These are definitely worth a watch!

PCB design is as much art as science, and we’ve discussed this subject a lot. Here’s our simple guide to rocking RF PCB designs. There’s also a lot of devil in that detail, for example when understanding edge-launch SMA connectors.

Continue reading “A Simple Guide To RF PCB Design” →