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