# Voltage from a transmitter

#### Drmario5237

Joined Oct 14, 2018
65
Hello. I'm thinking about building a rf energy harvesting circuit and would like to know how to figure out exactly how much voltage I would get from a transmitter saying I'm using rabbit ear dipole antenna and the transmission is at 12,000 watts from sources. Is inverse square law the only way to find out, is there another way and if it's inverse square law how do I formulate this with only knowing the watts and distance from transmitter. Also where I could have caring distances from transmitter can I use zenner diodes to regulate the voltage. And where I don't burn out the zener diode should I incorporate a resistor or PNP transistor before the diode. Thanks.

#### nsaspook

Joined Aug 27, 2009
6,714
The bottom line is energy as you can easily transform even small amounts of energy over time into a higher voltage but equivalent total energy.

The free space path loss uses inverse square law in a much easier format to handle power loss calculations. Unless you are in the 'near-field' (a few physical space wavelengths of the transmit frequency) of the source antenna I don't think you need to worry about component failure.

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#### BR-549

Joined Sep 22, 2013
4,938
As you move out away from an EM source, the RF pattern is like concentric rings around the source.

An antenna catches one ring at a time as it moves from source.

You can add elements to catch multiple rings at the same time.

What really is neat about this is......that the elements need a certain configuration, but the antenna itself, can be any distance from source.

#### Drmario5237

Joined Oct 14, 2018
65
As you move out away from an EM source, the RF pattern is like concentric rings around the source.

An antenna catches one ring at a time as it moves from source.

You can add elements to catch multiple rings at the same time.

What really is neat about this is......that the elements need a certain configuration, but the antenna itself, can be any distance from source.

#### BR-549

Joined Sep 22, 2013
4,938
You would want to study antennas. There are many types and configurations.

Generally there is a "driven" element, "director" elements and "reflective" elements.

Harvest is the wrong word to describe this, because it implies bounty.

It's more like mining trace minerals. A lot of trouble for very little payback.

So far anyway. This might change in the future.

#### nsaspook

Joined Aug 27, 2009
6,714
The reality of Energy harvesting.
https://semiengineering.com/the-limits-of-energy-harvesting/
“If you’re not burning a lot of energy, there is no need for energy harvesting,” Gert Jørgensen, senior vice president of sales and marketing for Delta’s ASIC Division. “And if you do burn a lot of energy, then energy harvesting will not work. Where we see this working is in the 10 milliwatt to 100 millwatt range, but a battery is still 20 times cheaper. Energy harvesting technology is big. You have the harvesting element, power management and storage. If you compare that to a battery, the battery is smaller.”
It's mainly hype generated by people looking for research funding.

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