Maximum transmitting distance

[mstechca]

I have a transmitter and a receiver, both with antennas. If I used a DMM to measure the current, power or voltage from any antenna to ground, is there a way to determine the distance?

If so, what equation do I use?

 

[_3iMaJ]

You want to start with what is called the Friis equation. Its basically the Ohm's law to wireless communication. But it requires you have different knowledge than you do. Look it up and get familiar with it and we'll talk more.

Just an FYI this equation only considers transmitting your signal in freespace, so it won't do you much good if you're going through walls, trees, etc...

Its the BEST CASE scenario.

 

[Russlk]

It is not likley that a DMM will measure the antenna voltage or current. What is the frequency? Since you have both transmitter and receiver, why not measure the distance?

 

[mstechca]

I dont just measure it because it is a waste of time, and the voltages in several batteries vary significantly. Most of them are at least 1/2 dead.

I understand ohms law, but I don't understand how it applies to wireless communication.

 

[_3iMaJ]

I dont just measure it because it is a waste of time, and the voltages in several batteries vary significantly. Most of them are at least 1/2 dead.

I understand ohms law, but I don't understand how it applies to wireless communication.

You misunderstood what I wrote. I said the Friis Equation is LIKE ohm's law for wireless communications.

Let me repeat that, you're interested in the Friis Equation, NOT ohm's law.

 

[mstechca]

what is the difference between the friis equation and ohms law?

 

[_3iMaJ]

Look up the Friis equation and you'll see.

 

[mictester]

I have a transmitter and a receiver, both with antennas. If I used a DMM to measure the current, power or voltage from any antenna to ground, is there a way to determine the distance?

If so, what equation do I use?

You can't use a DMM to measure RF. You can't determine how far a radio signal will travel... There is a basic rule-of-thumb (Friis equation) but it's only a vague approximation (at best).

Your effective range will be determined by a huge number of variables, including: Transmitter Power, Receiver Sensitivity, Required Bandwidth, Terrain, Obstacles, the direction of the wind, day of the week etc.....

The only real way to find out is to try it! Even the big broadcasters just use calibrated receivers (to measure field strength) and drive around their target coverage area. All the calculations in the world won't account for real world conditions.

Mike