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Tech Note: Radio Power vs. Distance

Myth: Doubling the power will double the distance of my transmitter.

It is a common misconception that in order to achieve twice the distance in a radio link, you can simply double the power. The reality is that in order to double the distance, 4 times the Tx power is needed. This rule comes from a simple geometric formula: the propagation of radio waves expands in the shape of a sphere, and the surface of a sphere (and thus power density) changes proportionally to the square of the radius (in this case the radius = distance).

To put it simply, if with a 1 Watt transmitter you can reach 1 mile, in order to reach 2 miles you will need a 4 Watt transmitter. Of course the distance depends not only on the power of a transmitter but also–and very much so–on the antenna gain and height, the quality of the receiver and on the obstacles in the terrain.

A very useful way to calculate radio links parameters is using dB’s. In this case, mathematics show that doubling the power is the equivalent to increasing the power by 3 dB. It can also be demonstrated that doubling the distance is the equivalent of an increase by 6dB.

Seen below is a table of equivalence between Watts and dBm.

1 mWatt  =  0 dBm    
1 Watt     =  30 dBm     2 Watt   =  33 dBm       4 Watt   =  36 dBm
10 Watt   =  40 dBm    20 Watt =  43 dBm     40 Watt =  46 dBm

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New firmware and software releases

New software and firmware has been posted to our site:

Satel Configuration Manager 1.5.5: Supports the M3-TR8 module and new TR3/4/8 firmware revisions. Also includes minor bugfixes. Download from our software page.

SATELLINE M3-TR3/TR4/TR8 firmware version Supports M3-TR8 module, fixes miscellaneous minor bugs. Download from our firmware page. Note: Requires Configuration Manager 1.5.5 or higher due to changes in firmware internal structure.

SATELLAR 1/2/10/20DS Radio Unit (RU) firmware version Minor bug and stability fixes. Download from our firmware page.

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Introducing the SATEL-LP line of wireless I/O

We are proud to offer a new product line of wireless I/O communications. The SATEL-LP line of radios and snap-on I/O modules are simple to configure (no programming or software needed), and will save time and money versus running wiring conduits. 900 MHz and 2.4GHz radio modules ease logistics, as no licence is needed.

These systems can operate in 3 modes:

  • Wire-in, wire-out
  • Wireless I/O to Modbus (control LP I/O modules with Modbus, without any extra hardware)
  • Wireless serial RS-232 and RS485, providing a simple link between PLCs or RTUs

A wide variety of I/O modules are available for digital in/out, analog in/out and more. See the linked brochure below, or check out the product pages for the SATEL-LP24 (2.4GHz radio), SATEL-LP9 (900MHz radio), or the full line of SATEL-LP expansion modules. Contact us for more information.

SATEL-LP Brochure