new module, with BLE module, Sparkfun Micromod, bad RF design or not? - Page 1
Forum section: electronics / projects

author: nuclearcat
author_rank: Unknown
timestamp: January 19, 2021, 07:51:39 pm
content: Sparkfun released new board. Just for sake of learning, as often stereotypes turn out to be untrue, isn't such position of module antenna dead wrong for 2.4Ghz?Copper pour + not near PCB corner.As i recall ESP32 in module guidelines require quite big keepout area near antenna.Or it doesnt matter?

author: Ian.M
author_rank: Super Contributor
timestamp: January 19, 2021, 08:22:15 pm
content: Yep. Page 14 of the Raytac MDBT50Q-P1M module datasheet found in the documents tab of the Sparkfunproduct page, basically says *DON'T* do that! Range will obviously be reduced, and I'd bet it will have undesirable directional characteristics. It would appear that someone at Sparkfun didn't RTFM!

author: thm_w
author_rank: Super Contributor
timestamp: January 19, 2021, 11:21:11 pm
content: I would have preferred shift it to the left and overhang the side of the board. As they've done here:https://www.sparkfun.com/products/15025I left a comment copying what Ian has said.They seem to be copy/pasting layouts to save time as its essentially the same as this board:https://www.sparkfun.com/products/16401

author: mxhll
author_rank: Contributor
timestamp: January 20, 2021, 05:07:43 pm
content: Anyone worked with Raytac Modules before?They are not readily available from distributors, but they seem to have a layout-friendly LGA pattern,as opposed to some of the competing nRF 528xx modules.Lairds BL654 module immediately pissed me off because they gave all the nRF pins new names, probably for their own embedded toolchain or whatever.Edit:The Sparkfun board has a cutout of the copper pour beneath the antenna. See screenshot of rendered gerber from their github, if that is the board you meant:https://github.com/sparkfun/MicroMod_Processor_Board-nRF52840

author: Ian.M
author_rank: Super Contributor
timestamp: January 20, 2021, 06:31:19 pm
content: Even with the cutout it still violates the layout recommendations. See second bad layout on page 14 ofhttps://cdn.sparkfun.com/assets/learn_tutorials/8/2/0/Raytac_MDBT50Q.pdf

author: mxhll
author_rank: Contributor
timestamp: January 20, 2021, 06:42:57 pm
content: And the micromodule will end up on a M.2 carrier PCB, probably with no cutout at all.Maybe they were constrained by the layout and didnt want to go to four layers.Not optimal but if they have decided the performance is adequate?I like the M.2 module approach

author: thm_w
author_rank: Super Contributor
timestamp: January 21, 2021, 10:41:33 pm
content: Quote from: mxhll on January 20, 2021, 06:42:57 pmYeah I didn't even think about 2 layer, which is difficult, all of those 7 traces would have to go under the module somehow.The board is so small though, 4 layer cost is quite low, maybe 3c each vs 6.5c each from JLC.

author: mxhll
author_rank: Contributor
timestamp: January 22, 2021, 09:34:24 am
content: Oops I turned off inner layer 1&2, so they actually use a four layer board.I think they could have done a better job at laying this board out. Now I think there is no reason to keep that module in the center.The inner layers are probably power and ground, but are heavily separated by random tracks crossing through them.They could have avoided the copper pour on the top and bottom layer with all these islands.I dont know if they were restricted on their IO routing,but I have a feeling a custom board support package would have been a better solution than the massive use of vias on their IO lines.What do you think? I'm no expert in layout but also not impressed by this example

author: nuclearcat
author_rank: Unknown
timestamp: January 22, 2021, 01:35:59 pm
content: Quote from: mxhll on January 22, 2021, 09:34:24 amI was terrified by this example...But i'm also not very experienced, so i thought maybe i am missing something and such things are allowed.