37

Makezine's writeup on the Pi 3 this morning included a somewhat tantalising section:

Photo of the Pi 3 rear

The other interesting thing on the back of the board, right next to the wireless radio chip, is something that looks like an unpopulated UFL antenna, labelled J13 on the silk screen. You can just seen the board’s antenna in the image above on the flip side of the board directly below the unpopulated contacts.

While we’re not going to get any support from the Foundation — it would break the terms of their FCC certification to document it — I’m looking forward to the first hack to add a cantenna to the Raspberry Pi either by desoldering the on-board antenna, or making use of those unpopulated pads on the back of the board. Cheap long range Wi-Fi is just a Pringle’s can away.

Does it sound plausible that a long-range antenna might be connected to the J13 pads shown in the above image? Are similar kludges available on other small single-board computers, and if so what kind of performance might be expected?

  • This is a very broad question. It is of course plausible; whether it's practical cannot be determined yet. – Jacobm001 Feb 29 '16 at 17:39
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    As to 'of course plausible', I have no way of knowing that without referring to experts. As to 'cannot yet be determined', that's not really true is it? Review units have been in the field for several weeks and I can't rule out the possibility that a reviewer might just read this board. – goobering Feb 29 '16 at 17:46
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    It is important to know whether soldering a U.FL connector in place would work; Even more so when one would like to put the Raspberry Pi 3 in a metal enclosure and still use its WLAN. – Serge Stroobandt Mar 3 '16 at 16:46
  • You'd need a very fine soldering iron and a very steady hand - I think you would have to reposition at least 2 SMD links (0 ohm resistors - the green ones) I think. – SlySven Mar 4 '16 at 5:07
  • I put a section of the Raspberry Pi 3 into a Pringles like cylinder with the antenna exposed, but the file system became corrupted multiple times. Very interested in beefing up the wifi capabilities. Thanks for the discussion – energyi Mar 15 '16 at 23:30
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Yes, it can be done, but beware of violating FCC.

Details here: External antenna modifications for the Raspberry Pi 3

  • Why would it violate any FCC regulations? Wifi uses a dedicated spectrum... – Cerin May 11 '16 at 7:11
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    @Cerin I think Ward is referring to maximum power output, mismatched antennae 'poisoning' the with foul signals and things like that. – Mast Jul 15 '16 at 19:17
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    Why do you mean by "beware"? FCC only cares about you if you sell something as a product, they won't inspect your home or garage. – Dmitry Grigoryev Nov 30 '16 at 18:43
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    Actually, if you interfere with any legitimate use of the airwaves by exceeding the allowed parameters, the FCC can prosecute you. They have charged people for violating the regs in the CB spectrum, although I'm not sure any actually went to court. – MAP Jan 13 '17 at 5:53
3

There are two mostly unrelated issues. One is FCC certification as discussed above, the other is WiFi certification.

FCC certification is concerned with radiated RF energy across broad spectrums, mostly to protect other consumer electronic equipment like TV's radios, etc, from unwanted interference. FCC certification is required for devices sold in production (there is an exemption for experimental and prototype equipment as long as it's not so bad that it messes up your neighbor's TV reception) and anything that has any kind of clock or frequency generator higher frequency than 10,000 Hz has to be tested. So it's not even so much the radio as the processor clock etc that might radiate. However is adding an external antenna to the WiFi radio causes the device to exceed allowable RF energy in some of the bands that are tested, it would be a problem if you want to sell the device this way. The R-Pi foundation would not want to get involved in this kind of activity since they DO sell the board and if they help by providing info about modifications, and those modified systems cause problems, it could come back to them.

The second issue is related to the WiFi regulating council (not sure of the official name) which is more concerned with interoperability between available WiFi devices. Any device sold with the "WiFi" logo, has gotten a blessing from this organization and participated in extensive "plugfests" and interoperability testing to ensure that the device plays well with others, including operating at power levels that don't drown out other devices.

Again, the RaspbPi folks have gotten these certifications as well, and by connecting different configurations of antennas etc, these things could be violated. Or you might just put too much strain on the RF output amplifier and burn it out. In either case I can certainly understand why the organization would not want to do anything to cause them some liability for hobbyinsts messing around.

All that being said, as has been mentioned above, if you are just building a on-off version for your own interest, there is no real risk other than you might have to spend another $36 when you fry your board.

IMHO

  • No, the issues are pretty much related. If a device has RF functionality, it has to be certified as an intentional radiator in terms of FCC. – Dmitry Grigoryev Mar 12 '18 at 7:42
  • If you want to google more look for EIRP wifi power limits. In short, the limit is on how much power is put out in the strongest direction. improving the antenna can push a device over this limit, in only one direction. (antennas cannot create more energy). if you want to run more power you can get an amateur radio license (US) and use the dedicated band just below the Wifi band. – Arthur Ulfeldt Feb 20 at 20:21
1

It sounds a bit strange that RPi Foundation is concerned about breaking FCC certification by documenting the UFL connector site on their board. There are many SBCs which have a UFL connector onboard by design, e.g. Banana Pi M2+:

enter image description here

The presence of this connector didn't prevent this BPi from getting its FCC certification.

As an owner of a BPi (not this model exactly, but equipped with onboard WiFi as well) I can say that the performance of the antenna shipped with the board is decent, but not stellar. I have also tried out this antenna which improves the range by a few meters.

To sum up, don't expect drastic improvements from passive antennas, and in case of the RPi 3 be ready to get worse performance, since the schematic was optimized for the onboard antenna and may not match the impedance of UFL antennas and cables.

  • Many laptops have UFL connectors too and the are certified by FCC – Suici Doga Mar 10 '18 at 8:39
0

It could violate FCC because if you connect a non well impedance adapted antenna, it could emit harmful harmonics for other devices nearby

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    This has really already been covered by Ward's answer, and its accompanying link, above. – goobering Jul 13 '16 at 14:28

protected by goldilocks Dec 1 '16 at 2:43

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