dBm versus µW/m² - Page 1
Forum section: electronics / general

author: jancelot
author_rank: Regular Contributor
timestamp: February 09, 2017, 04:10:46 pm
content: The Aaronia Spectran HF-80120 V5 has an AVG Noise Level (1Hz) with PreAmp of -150dBm/Hz.The Gigahertz Solutions HF59B has a Power flux density of 0.01 - 19,990 µW/m².What is the difference between them and how do I convert between units? Which one is the recommended to get?-http://www.aaronia-shop.com/products/spectrum-analyzer/real-time/fastest-portable-spectrum-analyzer-https://www.gigahertz-solutions.de/en/rf-and-emf-meters/high-frequency-rf/meters/338/hf59b

author: TimFox
author_rank: Super Contributor
timestamp: February 09, 2017, 08:01:12 pm
content: "dBm" is a measure of power, specifically decibels above 1 milliwatt of power (at an impedance level that should be specified)."dBm / Hz" is a measure of noise power per unit bandwidth. Multiply by the system bandwidth to obtain the noise level, referred to the input of the device. The theoretical minimum (thermal noise) is -174 dBm/Hz at 300 K (nominal room temperature)."uW/m^2" is a measure of radiated power density, which means that you put the electrical power into an antenna.

author: jancelot
author_rank: Regular Contributor
timestamp: February 10, 2017, 07:34:35 am
content: Then, in the case of the Spectran HF-80120 V5, how can I get the equivalent µW/m² value, or it's not possible? Which device is best to determine electromagnetic radiation inside a building?

author: ap
author_rank: Frequent Contributor
timestamp: February 10, 2017, 10:22:37 am
content: First of, you are comparing a noise density of a spectrum analyzer to a power density measurement range of a power density meter. Two different things, having nothing at all to do with each other. Its a little bit like comparing a digital voltmeter noise (last digits uncertainty, digits toggling with no signal connected) to the measurement range of a power meter.Not sure what you want to do, you do not tell us. Normally, if you are interested in the impact of electromagnetic radiation on the human body, the mW/m2 is the one you are interested. If you want to measure the EMI as per e.g. FCC, you cannot just do this in a room. You need a special setup. (And anyway, you are in the wrong section, should go to RF forum for more attention.)The Aaronia should give you a fieled strength (dBuV/m), with an antenna. It is a combination of the antenna used and the measuring device. The antenna has different sensitivities at different frequencies. So it is not just a simple multiplication. You can then calculate a power denstity through the free space impedance, 377 ohms. Pd = E^2/377. But that is (spectrum!) at a given frequncy. You probably want to know the overall power, the integral over the frequency spectrum. You cannot do that with your means (unless the Aaronia can do that for you, have not checked that).But keep in mind: based on the question you ask, it may not be the best idea to spend money on this (assuming you want to know electrosmog), given you do not have the necessary theoretical background. If you are interested in electrosmog, consultants can do that for you and also explain the test results. Also, an intentional emitter (like a cell phone or wifi device) generate higher EMI levels than e.g. a computer just radiating due to internal clock sources. Alternatively, if you do not want a consultant, a power density meter is as simple as it gets for you. But again, what then do you measure and what do you derive from the results?