Is there any advantage to a metal case over a plastic case for a G7RPG server? Pros and cons?
Good question. I have recently done some experimenting with several nodes I’ve built (see this Article), some with metal cases, some without, and I definitely prefer to have a metal case as it looks nice, provides a nice solid enclosure to mount things in and on, and should help to minimize EMI/RFI to a small extent, however in my tests so far the nodes with metal cases around the audio interface and power supplies have not actually made any noticeable difference in audio quality or RF performance.
What has been much more important is the proper placement of ferrite filters to reduce conducted RFI on various cords and wiring. Wavelengths of 70cm - 2m will much more easily couple to for example a 1 or 2 foot long wire or cable, than to a small radio, or interface PCB which have only short traces and tiny surface mount components. So a plastic case or no case at all should be fine as long as you have ferrites on various switching power supply cables and audio cables that are anywhere near to a 500+mW transmitter.
Additional filter caps on the power supply are also a good idea. This can all vary quite a lot from node to node however so you just have test it and if you hear any noise or have any RFI issues to/from the node start trying ferrites in different places and then maybe add some extra (2000+uF) capacitance on your DC power lines.
Another advantage of metal cases is they can provide a little better of a ground plane for the transmitter. If using an HT you have almost no ground plane and the SWR seen by the HT can vary all over the place. Not a big deal for occasional handheld use but for a node that may be transmitting hours per day that could affect its longevity. Having a nice metal enclosure and/or a grounded power cord can help reduce RF reactance and improve the overall Tx & Rx performance. Definitely helps on regular HF and VHF/UHF radios, which always have a ground terminal connection on the back and always recommend in the manuals to run a ground wire to an actual ground rod. Taking a similar approach on a node could only help, though this does require some common sense in the configuration of the wiring, enclosure(s), and the antenna. If the HT is mounted in or on/near a metal enclosure with short ground wires and a star-grounding configuration and these are not obstructing the antenna it should provide a slightly better ground plane and more consistent load impedance to the transmitter and thus better radiation efficiency. RF is often hard to predict though and actual testing will usually tell you a lot more than general recommendations.
Generally speaking, a metal case is advantageous where RFI/EMI interference could be a issue.
But only if you get very close to 100% shielding.
That can entail sinking or shedding rfi/emi that may be captured on any wires leading to the device with things like feed-through capacitors or ferrous beads etc.
Depending on the level of hostile environment would depend on just how far you may want to go in preventative action.
And of course, rfi is a 2 way street as well in keeping it contained or reduced from other near items.
Most do nothing unless it is a problem, but most also ignore looking for it when there is a problem.
Just some food for thought. I know nothing of the device itself.
Thanks for the thoughtful and detailed answer.
I appreciate your insight on the subject…food for thought.