[Hack] Extending the bluetooth range of the 121GW - Page 1
Forum section: electronics / projects

author: gnif
author_rank: Unknown
timestamp: September 19, 2019, 09:32:19 am
content: Recently I have found the Bluetooth feature in the 121GW invaluable, however it's range is a bit lacking and upon inspection it's clear why. The Bluetooth module is behind an EMI shield and behind the batteries. I didn't want to alter the meter by removing/altering the EMI shield, it's clearly required, so instead, I modified the Bluetooth module for an external antenna.A quick google turned this up, it's pretty simple to do, but you must be ready to work with extremely fine pitch parts (I lost the capacitor and had to steal one from a donor Bluetooth module).https://www.silabs.com/community/wireless/bluetooth/knowledge-base.entry.html/2015/08/06/_how-to_modify_ble-QAnIOnce done, I grabbed a WiFi antenna (seems to work well enough) and cut it apart and down to fit it inside the chassis without making any alterations. Just used some hot snot to keep it in place.Did it work? Yeah!Before I could get a flakey connection from the adjoining room (~5M), now I can connect to it from the other end of the house (~20M away).

author: Terry01
author_rank: Frequent Contributor
timestamp: September 19, 2019, 09:35:09 am
content: Nice job!

author: thinkfat
author_rank: Unknown
timestamp: September 19, 2019, 11:48:40 am
content: Nice job! What size is that capacitor? Smaller than 0402?

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 19, 2019, 11:59:52 am
content: Quote from: thinkfat on September 19, 2019, 11:48:40 amThe article says: 27pF/6.3V/C0G (package: 0201)

author: mikerj
author_rank: Super Contributor
timestamp: September 19, 2019, 12:42:11 pm
content: Useful mod, but I would be a little concerned that the antenna is held with hot snot just above the input terminals. If it falls down and shorts something out you'd have quite a surprise if you tried to measure a high energy circuit (with the Cat rating of the meter I mean).

author: gnif
author_rank: Unknown
timestamp: September 19, 2019, 01:03:16 pm
content: Good point, I might throw some epoxy in there instead

author: ThomasDK
author_rank: Regular Contributor
timestamp: September 19, 2019, 05:02:57 pm
content: Quote from: gnif on September 19, 2019, 09:32:19 amI would call it a "fix" rather than a "hack"... That's a pretty awful RF-layoutThese modules are meant to be mounted at a board edge, with no copper near the antenna. Someone didn't read the datasheet:

author: Micah Lindstrom
author_rank: Contributor
timestamp: March 29, 2025, 02:45:36 pm
content: Wow, that's amazing! Why can't the antenna be fully insulated with some shrink wrap? RF should pass right through the plastic insulation.I'm a bit overwhelmed by antenna selection. The connector is U.FL, and there are adapters to get SMA connectors too if desired for whatever reason. Digikey has 79 U.FL antennas at this time.https://www.digikey.com/short/70cz7cp7It seems ideally the antenna length should be quarter, half, three-quarter, or full-wave. Full wave is λ=v/f=c/f=299,792,458m/s / 2.4GHz = 299792458÷2,400,000,000 = 124.9mm at the low end of frequency range and 299792458÷2,483,500,000 = 120.7mm at the high end of frequency range.So antenna lengths of 30.2–31.2mm, 60.4–62.5mm, 90.5–93.7mm, and 120.7–124.9mm are ideal for Bluetooth. It also seems antennas can be longer than full-wave for even better performance. I also see flat antennas likehttps://www.digikey.com/short/8r9zt3dmFor referencehttps://www.digikey.com/short/3m9pb5dfhttps://www.digikey.com/short/03w8fqb7