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HAT blocks or weakens WIFI

Posted: Mon Mar 25, 2019 2:45 pm
by jeremybirch
I am in the process of developing a HAT design, and my first prototype works OK on a Pi 3B+ but with one major drawback - it seems to block much of the WIFI signal from the board so that it is only visible to other devices from a narrow range of directions.

I suspect this is because my board has quite solid ground planes and of course due to the HAT spec is lying directly over the Pi antenna but 11mm or so away.

Does anyone know how large an aperture I need to make in my HAT design's power planes to allow for a good WIFI signal?

Re: HAT blocks or weakens WIFI

Posted: Thu Apr 04, 2019 10:52 pm
by alphanumeric
I can't answer your question directly but may have an alternate solution? Maybe putting more distance between your Hat and the Pi may help?
Maybe a booster header, https://shop.pimoroni.com/products/booster-header
and taller standoffs https://www.adafruit.com/product/2337
Or a stacking header, https://www.adafruit.com/product/1979 and tall standoffs?

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 12:40 am
by hippy
Maybe perforate the ground plane near the antenna, add some holes or slots the radio waves can 'leak through' ?

You can probably prototype and experiment with an un-etched copper clad board tied to 0V.

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 8:21 am
by mattmiller
JAAMOI Where is the wi-fi antenna on a Pi3B+ ?

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 8:30 am
by alphanumeric
mattmiller wrote:
Fri Apr 05, 2019 8:21 am
JAAMOI Where is the wi-fi antenna on a Pi3B+ ?
Its that triangle shaped indentation on edge of the board right next to the WIFI chip.

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 8:48 am
by mattmiller
#LOL
I looked for a triangle shape but couldn't find it it (eyesight genuinely not good any more) - what big thing is it near ? :)

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 9:05 am
by hippy
To the left of the metal-cased WiFi module, between the mounting hole and connector. The "Made in the UK" silk-screening passes over it -

https://www.jeffgeerling.com/sites/jeff ... d-logo.jpg

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 9:25 am
by mattmiller
Got it now ta - didn't know the metal thing with raspberry logo was the WiFi chip!

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 11:15 am
by hippy
There's a rather nice x-ray of the 3B+ WiFi module giving an inkling of what's under the hood and showing the antenna off to its left here -

https://blog.pimoroni.com/content/image ... ll-6-1.jpg

I'm sure there was a photo of the WiFi module with its casing removed but can't currently find that.

As I understand it, turning the WiFi into a module meant it could more easily be used on other Pi variants such as the 3A+, can be certified without having to go through a more involved, more costly, testing process.

Re: HAT blocks or weakens WIFI

Posted: Fri Apr 05, 2019 11:37 am
by fruitoftheloom
hippy wrote:
Fri Apr 05, 2019 11:15 am
There's a rather nice x-ray of the 3B+ WiFi module giving an inkling of what's under the hood and showing the antenna off to its left here -

https://blog.pimoroni.com/content/image ... ll-6-1.jpg

I'm sure there was a photo of the WiFi module with its casing removed but can't currently find that.

As I understand it, turning the WiFi into a module meant it could more easily be used on other Pi variants such as the 3A+, can be certified without having to go through a more involved, more costly, testing process.

This blog has good pictures / description:

https://www.google.com/amp/s/blog.pimor ... dware/amp/



https://www.raspberrypi.org/blog/raspbe ... le-now-35/

Dual-band wireless LAN and Bluetooth are provided by the Cypress CYW43455 “combo” chip, connected to a Proant PCB antenna similar to the one used on Raspberry Pi Zero W.

Re: HAT blocks or weakens WIFI

Posted: Thu Jul 18, 2019 2:25 pm
by strebor54
Hi all, has anyone seen any guidance on not compromising the WiFi performance with HATs etc.
I want to mount a beam forming mic above the pi and there will be IR blaster plugged into the IO header.

Thanks Strebor

Re: HAT blocks or weakens WIFI

Posted: Wed Jul 24, 2019 9:20 am
by Allen Liew
I'm planning to design HAT for the Pi4.
Concerning the WiFi signal might not be strong enough because the Pi4 will be placed inside a total seal metal case for water proof, can i add external antennas to the WiFi ac ? if so how to connect them to the Pi4 board?
Thanks for attention,
Allen

Re: HAT blocks or weakens WIFI

Posted: Wed Jul 24, 2019 4:35 pm
by hippy
Allen Liew wrote:
Wed Jul 24, 2019 9:20 am
can i add external antennas to the WiFi ac ?
Not without invalidating its certification. You can use a USB Wi-Fi adapter which allows an external antenna to be used.