Minimum transmitter and receiver distance

Hi all,

i am wondering what is minimal distance between receiver and transmitter, because when I put close to each other, class 1 Bluetooth transmitter, on the receiving side, I am receiving packets within wrong channel. Channel number is fixed in transmitter.

Thank you

Shouldn't happen with high quality transceivers, review the max. receive input level specification, it's usually higher than the transmitted power. There's a certain risk, that the bluetooth receiver is O.K. but your serial interface mixed up by the RF level, due to bad circuit layout.

Bluetooth receiver specification mention a -20dBm maximum input power at the antenna connector, where the receiver must report correctly the BER and RSSI (if is the case). Usually good BT receivers support (decode data) at higher input levels, sometimes up to 0dBm.

Assuming a 0dB antenna gain on each BT device, if you put them side by side, there is a possibility to get wrong data (due to intermods) if one of them is not working very well.

The transmitter is `official′ Bluetooth development kit, and receiver is from Ubertooth project. It uses Chipcon′s CC2400 transciever, with roughly 3 dBm saturation level at the input. Could it be due to near field pattern of the antenna?

In near field (inductive coupling) can happen things hard to be predicted, if the antenna was designed to work in the far field region.
Try to measure the level at the receiver antenna connector (using a spectrum analyzer), when the two antennas are coupled.
Also verify the maximum conducted level of the receiver if matches to the Chipcon datasheet specification.

I see even +15 dBm maximum receiver input specified for a connectBlue module. But it's called an industrial device, so the cheap ones may be considerably different.

Could you still see the packets on "right" channel? Or the packets can only be seen on wrong channel.

Near field effect should not affect the channel (or say the central frequency) of the received packets.

It sounds to me like a non-linearity effect.

is the CC2400 Power amplifier working in the linear region?Sufficiently back off from 0 dbm which seems to be the max Pout....
if this, it should discard linearity effects at the Tx....then we ll need to focus only on the receiver.