I am designing a prototype PCB which shall have 5 pluggable RF modules and one 4G LTE module as shown in the image

PCB with multiple RF and LTE pluggable modules

The Base board size shall be 240 x 140 mm, RF board size is 40 x 50 mm and LTE board size is 45 x 70 mm.

The 5 RF boards are identical and they operate in the 868 MHz band for short range communication. The center frequencies of successive RF boards shall be separated by 400KHz each (they use different channels in the band). The boards have transmit power capacity of 22 dbm.

The LTE module has a 3dbi antenna. All antennas are rubber duck type antennas. All the RF radios shall operate independent of each other.

The whole set (including antennas) shall be enclosed in a polycarbonate enclosure.

I tried looking at posts with the configuration like what I have, but I could not find any. I found couple of posts which talked about 2 or 3 radios on one board, but of different type and frequency bands.

My questions is as follows. Since all the radios are physically close to each other and operating independently (center frequencies of RF boards are also close to each other), will they cause issues at the receivers of each radio? Will the transmission from surrounding radios cause interference, saturation or reduction in data rate issues? Would any other issues crop up? Are there any specific points that I need to take care of?


1 Answer 1


Given low-Q (PI?) input matching filtering CLC networks in each radio between the Antenna and the Low Noise Amplifier, you will experience blocking. The channel spacing of 400KHz, at 900 MHz, requires Q of 900*2.5 or over 3,000X to be beneficial. I'd plan on at least 10 milliWatt (+10dm) of the radiated 150milliWatt, to couple into the adjacent antennas. Can your frontends (the LNAs, the mixers if there is no LNA) avoid the serious de-sensitization of an inband +10dBm interferer? IMHO if you expect success here, you must control TIMING of remote and local transmissions.

Additionally, 10 milliWatts may exceed the "safe constant exposure input power" of the receivers.

  • \$\begingroup\$ Thanks. Transmissions from the RF boards as well as LTE is not continuous, in fact very low. It will be difficult to control timing of remote transmissions, but we should be able to control local transmissions. Will this resolve most of the problems? Also, reducing the transmit power of RF modules will reduce the interference, right? Will it help? \$\endgroup\$
    – dndserv
    Nov 18, 2019 at 14:06
  • \$\begingroup\$ If your local receivers should be detecting and demodulating a remotely transmitted message at same time one of the local transmitters also sends, that high energy will block the weak remote signal. You may need to implement Acknowledge/Resend protocols. \$\endgroup\$ Nov 18, 2019 at 15:02

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