On Sat, 31 Dec 2005 09:44:45 -0800, "RST Engineering"
wrote:

It is a little like asking how to convert giraffes to file cabinets. THere
is no conversion factor from dBm to microvolts/meter. One is a power. One
is a field strength.

Hi Jim,

I would have to disagree with that. Field Strength is naturally
assumed to be a constituent of Free Space, or at least in a path
largely defined with an impedance of 120 · pi Ohms. Volts and Current
are convertible through this. dBm is likewise related to an
impedance. It is classically 50, 75, 200, 600, or 1000 Ohms depending
upon industry usage. Without this understanding (often implicit
within those industrial applications) the comparisons of dBm citations
would become quite strained (for instance, computing gain/loss).

If posed this same query of translating dBm to Field Strength, I would
presume the underlying basis of comparison would be that same 120 · pi
Ohms. This is hardly a stretch given Field Strength can also be
described in units of power and area. The proper usage in Field
Strength context would be
dB(re 1mW/m²)
where dBm is frequently a short-hand for
dB(re 1mW into 600 Ohms)
or
dBm(600)
where, perhaps the user actually meant
dBm(50)
Hence, a bald citation of dBm carries a lot of implicit baggage.

Suffice it to say that there are a world of dB conventions for
expressing relationships.

The simple lesson learned from the original question is that when both
sides of the equation do not balance in their units; then that
equation is incorrect. There were more errors than that, but the lack
of balance was sufficient to condemn its usage.

73's
Richard Clark, KB7QHC