Subject: [softrock40] uV/m to dBm

> There's a frequency factor that must be included when converting between

> field strength in uV/m and signal power.

>

Thanks for giving me the relavant information Jack.

I did actually find these two sites but my mathematics teacher never told me all those formulae could be useful and interesting so I

tend to run a mile when I see them! So I missed the frequency related factor.

Now I make sense of the calculator.

73 Alan G4ZFQ

> From

> http://www.softwright.com/faq/engineering/FIELD%20INTENSITY%20UNITS.html

>

> E(dBµV) = E(dBµV/meter) + Gr(dBi) - 20log f(MHz) + 29.8

>

> P(dBm) = E (dBµV) - 107

>

> P(dBm) = E(dBµV/m) + Gr(dBi) - 20log F(MHz) - 77.2

>

> where P(dBm) is received power into 50 ohms, in dBm

> E is the received signal voltage in dBuV

> Gr is the receiving antenna gain in dB with respect to isotropic

> f is frequency in MHz

> E is the field intensity in dBuV/meter

>

> At 28 MHz, the -20 log f(MHz) almost exactly cancels the +29.8 so the

> received signal voltage equals the field strength plus antenna gain. But

> that's not the case generally.

>

> On-line calculators relating these factors can be found at many places

> on the Internet, e.g.,

> http://www.giangrandi.ch/electronics/anttool/field.html

>

> Jack K8ZOA

>

>