Bluetooth signal transmission

[skirj]

I have a bluetooth device that is setup to transmit data to my phone, and I am planning to use it in building a temperature sensing device in the ocean. Will this device be able to transmit a bluetooth signal through a space with the following dimensions (lxwxh): (13.5x5.0x1.5cm) to another device? The device will be surrounded by concrete except for the hole with those dimensions.

 

[VEBill]

This is essentially a Waveguide Below Cutoff question.

Here's a good starting point.

http://www.radio-electronics.com/info/antennas/waveguide/cutoff-frequency.php

Bluetooth is in the 2.4GHz band. Wavelength about 12.5cm.

Perhaps you could couple the signal into a coax to exit the structure.

 

[Comcokid]

Concrete will not completely block the signal even if it has some rebar. The signal will be attenuated, it's only a question of how attenuated it is and if there is still enough signal. I suggest you find a concrete building wall about the proper thickness (without the opening) and do an experiment.

Otherwise, you can put a 2.4 gHz rubber-duckie or other antenna, a short piece of coax through the opening, and another antenna placed with at least one or both of the antennas near the devices.

I used to design ISM band (915 MHz) devices made to forward propane tank measurements to a receiver connected to a phone line. On a few occasions the receiving device was located in a reinforced room where the phone line was available. Too much signal was lost going through the reinforced wall for the setup to work. The antenna-coax-antenna approach would work. This approach has its own signal loss but that loss was much less.

 

[itsmoked]

Are you two talking about simply a piece of coax with an antenna on the end closest to the nearest antenna - no direct connection to either unit??

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Comcokid]

In the setup I described it was a transmitting unit on a propane tank (Intrinsically Rated) about 30 yards from a reinforce room where there was a phone line. Outside the room was an antenna. This outside antenna had a coax that went through the reinforced wall and was connected to another inside antenna (about 4 feet of coax). This inside antenna was placed within six inches of the receiver, parallel to one side so it would be parallel to the receive antenna (the receiver had an internal PCB trace as an antenna).

Normally the transmitter/receiver would have enough link gain to work up to 1/2 mile line-of-site. But the room was a rebar reinforced concrete tornado shelter and panic room for a house. This room was reinforced on all six sides, and the house had metal siding.

 

[itsmoked]

Thanks Com!

Keith Cress
kcress -

http://www.flaminsystems.com