On Sat, Oct 29, 2022 at 07:47 PM, Raphael Wasserman wrote:
Also I got to the bottom of question about 20 dB difference between the results using Duffy's calculator vs. AF equation. The effieciency of small untuned loop antennas is around 1%, thus creating a 20 dB difference in the calculated results.?
But in a later post you say:-
The efficiency will be the same for tuned or untuned small loop antennas because neither radiation resistance nor loops ohmic loss can be changed
These seem to be conflicting statements, and I'm getting very confused about your definition of efficiency, which seems to be based on a specific theoretical definition. This may simply be a language issue, but I'm struggling to follow all of the discussion points.
In the 'real world', if you consider RF power in vs radiated power (or RX signal in) a tuned loop is demonstrably more efficient than an un-tuned broadband loop.
In the case of RX only, once an antenna has sufficient gain (or sensitivity) to be limited by the local noise floor, then it is not possible to improve the received signal to noise ratio, other than by changing the directivity (gain in specific direction(s)) of the antenna.
However for small broadband loop antennas, most do not have sufficient gain to be performance limited by the local noise floor (unless you are in an extremely noisy environment), and passive tuned narrow band loops (with a decent Q factor) will generally out perform broadband active loops of similar size, but only over a relatively narrow frequency range.
Regards,
Martin
