BT840E weak reception signal as central

[davidz]

Sorry this is an urgent request and we could not find much information on the internet about this module. We have a tight schedule so it might be a good idea to post here. . 

We are using Fanstel BT840E as the central in the gateway. We chose BT840E because it is FCC approved and claims to have a long range.

The SDK version is 1702. We found that BT840E gives extremely weak reception signal over the sensors compared to nrf52840 DK onboard antenna. The 3rd party nrf52840 MDK onboard antenna also gives much stronger reception signal compared to Fanstel BT840E, which claims to have much longer range.

We tried different antennas, checked cables and cut PCB boards but no success. 

Please find the comparison of signal strength between BT840E with external antenna and nrf52840 DK onboard antenna. They both use the same central firmware. 

BT840E reception signal:

nrf52840 DK reception signal:

It is hard to believe that BT840E has such a weak reception (15-20db lower than onboard antenna) with an external antenna. 

Your help is greatly appreciated. 

[Daniel Chisholm]

15-20dB is about what you lose when you have no antenna connected at all (i.e. just an empty u.FL connector).  Do you see a similar signal strength if you have no antenna attached?

Also, if you are using a u.FL to SMA pigtail, and connect an RP-SMA antenna or cable to that, there will be no centre pin present, so even though connectors are mechanically attached they are not electrically attached.

[davidz]

OMG, thanks so much Daniel. We did use a u.FL to SMA pigtail connector and tried several antennas. It turns out that all the different antennas we used have RP-SMA connectors. 

We did not suspect this because if we took off the u.FL connector, then BT840E could not receive any signals. So we always thought that the antennas are working. 

[awneil]