tricking out a cell phone for an external antenna - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: June 21, 2018, 01:26:36 am
content: Seeing the booster thread, I got an ideaSo I have some 0.03 inch hardline (very thin shit) and a cell phone that I have been thinking about augmenting so it has a SMA connector on it, so I can carefully analyze output performance and possibly add , filters, protection, external output data tap, directional antenna, etc to it (obviously not illegal amplifiers)I don't know much about how the output amplifier of cell phones is designed, but can I simply find the last point in the PCB before the cellphones antenna and solder in the hardline using minimal exposure of the center conductor of the coax? Do I need an impedance matching circuit? Cutting the trace right after the outputI kind of don't even know where the antenna is. Is it one antenna?Here is a picture I foundhttps://d3nevzfk7ii3be.cloudfront.net/igi/kKUarywLm6AbxEkF.hugeThe phone in question is a LG G4.My plan was to just use a nearfield probe to see where the signal is the greatest but I figure I would ask before I potentially destroy alot of money.Also, if I modded the chassis, would putting an RF relay or switch be feasible?I thought maybe this is difficult if they use some kind of highly integrated rf SOC where you can't intercept the analog data before an amplifier.I think it has something to do with that via stiched trace on the bottom of the picture, it looks like the most RF thing there.And I know the probability of success is low, but something interesting and complicated like a cell phone would help me learn this stuff better because its interesting, and maybe make me feel better about spending money on the PLUTOSDR, I get irritated when I cannot at least get some fun out of my machines.

author: tautech
author_rank: Super Contributor
timestamp: June 21, 2018, 01:38:25 am
content: This should give you some guidance to typical cell reception solutions:https://www.howtogeek.com/204961/how-to-easily-boost-your-cell-phone-signal-at-home/

author: CopperCone
author_rank: Super Contributor
timestamp: June 21, 2018, 01:43:58 am
content: I just want it to be clear I don't have signal problems or anything like that, I just wanna put a coaxial port/rf switch on the phoneI am also not interested in some kind of inbetween spoofing RF link, I want to physically modify the phone.. for my having less reception on the phone is better lol, its kind of a microwave leash/troll enabler

author: Neganur
author_rank: Unknown
timestamp: June 21, 2018, 07:31:35 am
content: Probably not much point in doing what you’re trying. Modern cell phones tend to have more than one antenna (I don’t mean Bluetooth/GPS/WiFi... but for the radio link itself) and they can be part of the enclosure, flex or thin metal sheet inside etc. also be careful not to introduce reflections to the link by blatantly having shorts or open circuit connections to the outside, it will kill the power amplifier very quickly.Those pictures from ifixit don’t reveal much that I can recognize but these three connectors look like something you’d use in production testing of the RF:

author: hagster
author_rank: Frequent Contributor
timestamp: June 21, 2018, 08:47:24 am
content: Hi Coppercone,Firstly, It's going to be difficult to do well.There are a lot of antennas on the LG G4 (and most modern smartphones). If you remove the clip on back cover from your phone you can see the antennas. Mine has labels like H8150 0435,H815 0423 etc. Each one of these numbers is a different antenna that the manufacturer can swap out to create a custom banded phone for a particular region. On your PCB photo you can see the spring contacts that carry the signal to/from the antenna. The two near the battery are the NFC and the 4 on the top edge are for wireless charging. The also seem to be some UF.L connectors that will be 50ohm. You might need to trace out where these go.See attached pic

author: CopperCone
author_rank: Super Contributor
timestamp: June 21, 2018, 01:54:09 pm
content: Hmm are these antennas spring loaded to the pcb and composed of metalized stuff on the phone body? They just look like unpopulated pads. The ufl connectors i missed.I like phones but i do not like the ultra high level of integration.Forgot there might be multiple antennas because of all the networks.Do they have high end android phones that have like all ufl connected antennas or something in the interests of hackability?

author: hagster
author_rank: Frequent Contributor
timestamp: June 21, 2018, 04:21:51 pm
content: They have to cover so many frequency bands these days it becomes impossible to do with a single(small antenna). Add in international roaming etc. Its an RF nightmate. I dont think there is a modern phone with a single simple antenna anymore.