RN-41 BT module very short on range

Wireless & IoT
1

Hello,

I did some development work on my breadboard using an RN-41 BT breakout from sparkfun. It worked really well, and at great distances on my breadboard.

Later, I developed and fabricated a PCB for the same circuit, and integrated an RN-41 module into it. Unfortunately, the range that I can transmit from my PCB is very short/weak - about 10 feet or so instead of 100+…

I verified that the RN-41 is set to transmit in it’s highest power mode, but I don’t think that is the problem. I feel that there is a hardware issue of some kind.

I do have a little bit of metal beneath the antenna on my PCB, in the form of my name, and a single trace passing by. It would surprise me if this was the problem, since my range limitation is so profound.

There are pads on the underside of the module that are supposed to be grounded per the data sheet, but research I did on this indicated that people generally don’t connect those. Thus, I didn’t connect them.

I’ve attached an image of both sides of my board, plus a schematic of the RN-41 connections. I sketched in the placement of the RN-41 in red, and depicted its antenna in blue. The RN-41 pads not shown as connected in the schematic are sitting on pads, but not soldered to them.

If anyone has any thoughts or experience on this matter, I’d really appreciate any suggestions.

Kind regards

2

That is a nice looking board, but I have little doubt that the trace and ground plane near the chip antenna greatly diminish its effectiveness. Also, the extra bit of PCB material below it changes the dielectric constant of the region. The antenna could be detuned or the impedance changed, which is disastrous. The chip antenna manufacturers give advice on board design: http://www.johansontechnology.com/techn … 80211.html

There are very detailed design notes on antenna design for PCBs (e.g. TI provides one for their CC2511Fxx series), which should also give some insight into the design considerations and problems that can arise. You could try removing the trace (replace with a wire somewhere else) and cutting and scraping away some of the ground plane near the antenna to see if that helps.