Reg Edwards wrote:
If you find yourself short of sensitivity, try a tuned loop in the
style of a magloop and match the antenna to the receiver.


In concert with an SSB rx of noise floor -135dBm in 2KHz Effective noise
bandwidth (they are realistic figures for an IC706IIG for example), the
rx noise in 2KHz BW is 0.04uV. With an antenna with AF=36dB, the rx
noise floor translates to field strength of 2.5uV/m or 8dBuV/m.

Clearly, the "instrument" is not going to be suitable for measurements
below 11dBuV/m. However, measurements of the BPL systems on "trial" here
(Mitusbishi based on DS/2 45Mbps chipsets) showed field strengths of 45
to 65dBuV/m in 2Hz and a rx with this loop needs 20+dB of RF attenuation
to keep the interference below the AGC threshold (with the benefit of
stabilising the rx input Z somewhat).

But whatever you adopt, accuracy will be limited by the uncertainty in
the amateur's receiver input impedance. This will change from band to
band and its actual value will be a matter of guesswork.

Yes, I have been measuring the rx noise floor with 20dB of attenuation
to simulate the common measurement configuration.


A receiver's input impedance can be masked with an attenuator. But
this further reduces sensitivity.


As discussed.

With amateur grade equipment, facilities and environment, expect a
measuring uncertainty in the region of 4 to 7 dB at 7 MHz. Which is
good enough for most amateur purposes and makes your precision
calculations, including conductor diameter and conductivity, not worth
the trouble.

Given that the interference is 70dB above the ambient noise floor, we
don't need 1/10dB accuracy to demonstrate to regulators that there is a
problem


All you need for calculation is enclosed loop area, loop inductance,
receiver impedance and a pocket calculator.

The uncertainty of a measurement is just as important as the value
itself. The only way to assess uncertainty is to compare with
professional-grade equipment. In which case, if professional grade is
obtainable, you can dump the amateur stuff.

Understood. My view is that if professional grade EMC measurement kit is
available, we can use it to do a lower grade calibration of the amateur kit.


I do like the way your calculations appeared on my screen with one
mouse click.
How do you do it?

The model is in Mathcad, I copied it to the clipboard and pasted it into
Frontpage (my web editor) which finds only a useful format in the
clipboard and saves it as a GIF file (ie a graphics image).

Thanks for checking the model Reg, I think you are telling me it is more
precise than needs to be, but you haven't faulted it for accuracy.

Owen