[BC] dbu to microvolts program

[Mark Humphrey]

Here are my calculations:

I normally work with 50 ohm equipment; so I'm most familiar with the
antenna factor equation for that impedance:

AF = 9.73/(lamdba * gain^0.5)

At 100 MHz, lambda = 3m, and the gain of a dipole is 1.64 times an
isotropic radiator

Therefore, at 100 MHz, AF = 2.53

In a field of 3.16 mV/m, this would produce 1.25 mV at the antenna terminals

This is equivalent to a power of -45.05 dBmW into a 50 ohm load, which
agrees closely with Richard's calculations.

However, when I convert from dBmW to voltage across 75 ohms, I get
1.53 mV, which is about 31 dB less than 55 mV, and I assumed no line
loss.  Am I missing something?

By the way, for a detailed discussion of antenna factor and how it
varies with frequency, see this paper:

http://www.tdkrfsolutions.com/DataPDFs/antenna_paper_part3.pdf

Mark

On 4/10/07, Richard Fry <rfry at adams.net> wrote:
>
>
> But as a rough calibration point, a matched, 1/2-wave dipole with no cable
> loss to the meter input would produce a power level of -44 dBmW when
> optimally oriented in a 100 MHz radiated field of 3.16 mV/m.  That -44 dBmW
> would produce about 55 mV across a 75 ohm measuring impedance (if my
> calculations are right -- somebody pls check me).
>