Total posts : 45366
Thanks much, Rich, for the fine tutorial on part 15 AM antenna theory.
Thanks for the links. I have constructed and used a RF ammeter similar to the one in the first link in your post. Since my scope works well into the RF spectrum (20 MHz) I use it as a detector rather than the diode and microammeter. Nothing wrong with the design, it is just simpler for me to use the scope.
I found the functional relationship between the secondary voltage and the primary current to be very linear over a wide range of currents. So, with this toroidal transformer I was able to measure the current into my antenna, but due to the phase shift of the transformer which does not agree with theory I was not able to get and actual power measurement. (Power = VIcos(theta) and theta was unknown). The antenna current did correlate with the field strength so this appears to be a decent way to peak tune an antenna/transmitter.
So, here’s a question for Rich: If the current measurement is made in the ground lead, would the voltage and current necessarily be in phase? It would seem to me that this is not a good assumption since the phasing would also depend on the antenna Z but I sometimes miss things.
Edit…I realized after I typed the above paragraph that I don’t know what voltage I am referencing. The new site is so fast I don’t have time to think as I type.
Another Edit…What I am getting at and did not state clearly is developing a way to measure the actual real power delivered to the antenna. It now seems to me the way to do this is to measure the antenna current and feedpoint voltage to ground. I can easily get the apparent power with my scheme, but as I mentioned the phase angle between the V and I with a resistive load does not match theory so I have no confidence in the method as I now use it. I am overlooking something obvious regarding the transformer, probably self inductance or using it as a voltage transformer rather than a current transformer. Just thinking out loud.