EMRFD Message Archive 4393

Message Date From Subject
4393 2010-03-03 06:52:05 Tim Carving up PC board construction, single-point grounding
I'm a big fan of dead bug, but when I made my R2PRO and had to worry about single-point grounding I used a different construction technique: started with PC board and carved out the traces with a sharp knive. Then peeled away copper (usually made easier by heating it up with a soldering iron) where it wasn't needed.

The technique isn't awful easy, and I can see how some have completely skipped this step and gone straight to a Dremel with a narrow cutter.

High densities are hard to achieve with a knife - i.e. doing a 0.1" DIP package is really at the edge of what I can consistently achieve - but I'm actually kinda proud of the result :-). I'll try to take some pictures.

On the subject of single-point-grounding: Dead bug did not cut it with the R2PRO and it's high audio gain. I might have thought that a big sheet of copper is a single point ground but I was wrong. The system was moderately stable with a pair of 600 ohm headphones at low to medium gains, but would break out in howling with a 8 ohm speaker. After reworking the ground system so that it was truly single point ground, isolating the headphone/speaker jack from the chassis, making a single ground point on the AF amp board, I am very impressed: the AF amp drives an 8 ohm speaker just fine, no howling, even with the gain cranked up all the way. The little 3904/3906 push pull pair gets decent volume to my favorite 12" instrument speaker (loud enough that if I leave the receiver on overnight, my wife and kids in the 2nd floor bedrooms complain when VK's start coming through on 40M at 5AM in the basement!)

Tim N3QE
4396 2010-03-03 08:48:35 g0kla Re: Carving up PC board construction, single-point grounding

I built the R2 (and the T2), rather than the R2 PRO, but I did use dead bug style. It seems to work well.

I built the AF section on a separate board which is mounted on plastic spacers and took the ground connection from a single place
4410 2010-03-04 05:17:17 Vojtech Re: Carving up PC board construction, single-point grounding
I have a similar experience with DC receiver, VK2DOB design with two Gilbert cell mixers.

The radio was laid out on two boards, VFO+TX on single board, RX+AF on other board. The RF+AF board layout was single sided. I did not have single sided copper clad board, therefore I just kept the ground and grounded it at each through leg connected to the ground on the other side. The receiver was curiously noisy and howled when loaded with speaker. I had to drill out a star shape out of the ground side around the AF amplifier, which is a considerable part of the DC RX. I had to do it with dremmel tool on populated board. Now the receiver works reasonably. The grinding is visible on my photographs.

73, Vojtech OK1IAK, AB2ZA