Ed Price wrote:
"Owen" wrote in message
...

Ed Price wrote:


So practically, since the average ham has a receiver with a sensitivity
in the order of a microvolt, then your antenna limits your minimum
discernable signal level to around 65 uV/m. Maybe 100 uV/m to be on the
safe side.

In fact, the technique calls for measuring signals on the rx from the
noise floor to about 20dB above it. The noise floor for receivers today is
typically -135dBm.


No, the technique does not use an S-meter. In a nutshell, it uses Ed
Hare's (W1RFI) technique for calibrating the noise floor of the receiver,
using an external attenuator to keep the rx input below the AGC threshold,
and measuring the audio output with signal and the audio output from rx
internal noise as inputs to a calculation of the input signal power.
Applying external attenuator losses, feedline losses and antenna factor
allows calculation of field strength.


Owen


IS Hare's technique published somewhere on the web?


Yes it is, see http://www.arrl.org/~ehare/aria/ARIA_MANUAL_TESTING.pdf .

That paper outlines the principle of using the known rx noise floor as a
baseline for measurements. I have developed a piece of software for
making the associated audio power measurements and automating the
calculation / documentation process.

Thanks for taking the time to review the loop model, it is appreciated.

Owen

PS: I saw your other response and Richard's suggestion that I use the
units capability of Mathcad. Sometimes the unit capability gets in the
way of readability, for instance I think you could not take the log of E
in volts / meter divided by V in volts and get dBV/m, I think you would
need to split E into two variables (say E' and l) and say
AF=20*log(E'/V)/l. Additionally, you can spend more time trying to get
the units to work, so that they don't collapse to fundamental units of
MLT etc, than solving the numerical side of the problem.