Replacement of RF-Cable

As i completely broke my RF-Cable (similar to FP2 Core module / antenna cable - with pictures) i need a replacement one.

I already messaged support (because for FP1 they were available in the store), but got the answer that they currently do not offer this as replacement-parts.

After some research i thought the connector was a common U.FL and ordered a cable for testing. Sadly it was the wrong one (My current suspects are MHF3 and MHF4).

Measurements for the connectors would be:
U.FL: 2.00mm outer ring, 0.5mm inner pin
MHF3: 1.4mm outer ring, 0.4mm inner pin
MHF4: 1.5mm outer ring, 0.45mm inner pin

currenly i soldered the old connector to my cable and have a big monstrosity taped onto the back of my phone (to get some signal… it is not as good as the antenna implies…):

Does anyone have measuring-tools precise enough to tell me if the RF-Interface is MHF3 or MHF4? A replacement-cable from ali-express would only cost 2.5$ and i would link the item after verifying it works for others facing the same problem in the future.

Suffering from bad radio performance I would be interested in this as well. I was already thinking about putting an SMA connector somewhere on the phone so I can at least experiment with external antennas.
And to add a second question: There is a similar looking but unused second connector pretty close to the actual RF connector. Is this connector meant to be used for external antennas ?

Did you experiment with different cable and antenna lengths ? Apart from the small size the core problem with a mobile phone antenna is to get properly matched and in resonance with the phones transceiver unit. Although most modern base band chips contain a facility that automatically tunes the antenna, a wide range of different radio frequencies is used today and antenna design is almost always a compromise.

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The antenna is supposedly an optimized GSM-Antenna (with piggytail-sma-connector) and cable & antenna came together and i hooked it up directly to the board…

But i don’t want that monstrosity back there anyway :wink:

you mean the connector on the other side near the sd-card-Slot? That is theoretically connected to the rf-module, but only used during final assembly of the phone with some kind of needle to inject a normed gsm-signal into the rf-system for testing-purposes/calibration. I don’t think there is a proper connector that will stick to that hole…

(I’m just guessing based on things i read - but this would make sense).

Thanks for the info about the connector. As a radio amateur I see lots of room for experimentation. I had another thought about using inductive or capacitive coupling to connect an external antenna.

The current hot shit is printing antennas on thin PCBs and just hook them up.
You could order 10 custom pcbs for 2$ from china and just have to decide on a fancy layout (maybe calculated & optimized).

Or fancy recursive things:

(better paper of optimized antenna for gsm-phones: )

There is currently no theory or model on how to design good antennas. Most of the research is just: lets try out cool shapes, do a physics-simulation, order them & test it in the lab.

Theoretically you could take any form of pcb and optimize an antenna for it (i.e. in the size of the battery fitting easily into the phone).

Sadly i have no time to dig deeper into that hole. :wink:


FP-Support sent me a replacement RF-Cable under warrenty. Came today, plugged it in, very good connection again :slight_smile:


If you really want to go crazy with RF you coud plug an HackerRF to the back-USB or the charge USB. Both can act as USB-Host and the software is available for android :wink:


done that already. Both HackRF and the (much cheaper and simpler) RTL-SDR sticks work excellent on the FP2 and Android in general. For anything below 60 MHz I now use a Red Pitaya - much more dynamic range with 14bit ADDA.

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They did really send you just the cable? The answer I got some weeks ago was
“Due to the damage that you have on the Fairphone, it would qualify as an out of warranty repair. […] According to our pre-diagnostic, it is very likely that the core module needs to be replaced. If that is the case, we estimate a minimum repair cost of € 378.05. […] The other option is to go to a local repair shop to see if they can fix your phone.”
Finally I fixed my phone myself with a magnifier glass, a pair of tweezers and some pliers. But I’m not very confident this will make it very long. How did you convince them to send you the cable?

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just the cable with the little PCB (bottom left to bottom-module) that i have spare.

The Label said on the package said “FP1-CAM-RU” - i think they just used some bag flying around :wink:

Still have no answer what the connectors are…

I have not expected of them to send me a replacement. I thought about buying MHF4-Cable and MHF3-Cable from ali based on a guess and see which ones fit.

While it would be cheap it would also take 30-60 days for the delivery to arrive… with no guarantee that they would fit…
(In that ali-shop you can find or order any combination of those rf-connectors… MHF1/2/3/4, U.FL, SMA, … you name it… even with the female pcb :wink: )

As i now have a precise caliper i measured the dimensions of the adapter:

about 0.3mm for the inner pin (with a bit error-margin as the caliper barely fit)
about 1.35mm for the outer ring.

With that i would deduct that this is an MHF3-Connector and the cable from Ali linked above should fit. Bear in mind that i have not ordered/tested it - but someone else with the same problem may try to throw 3 bucks & 3 weeks delivery time at the problem to fix similar things.

Maybe something for #groupbuy or #spareparts ?

Just for the records: After I read your post I gave it another shot and send another request for a replacement cable to support. In the end they have been sending me a cable from a broken/used phone (without any operational warranty of course) for free. And it’s working! :smiley:


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