```Dick PA0SE and others, Thanks for doing further tests for phasing. ``````> You did not comment on > the phase at the hot end of the coil compared to the cold end. I cannot measure the phase difference between currents in and out of the coil. I don't have a current probe with my scope but even if I had one the high voltage at the hot end necessary to obtain a readable current on the thermo couple ammeter in the aerial wire would make the applicatiion of a current probe impossible. I did look at the phase difference between the current at the bottom end ``````and ``````the voltage end the top end. Holding the voltage probe of the scope near ``````the ``````top of the coil was sufficient for this. Not surprisingly the phase difference was exactly 90 degrees, as far as ``````this ``````can be judged from a scope display. ``````My first reaction to this IS one of surprise. My first thoughts are that in a series resonant circuit (the loading coil in series with antenna capacitance and system resistance) the loop current would be in-phase (an I current) with the transmitter drive. My second thought on your observed phasing is that an input current Q at the cold end of the loading coil turns up as a similar magnitude quadrature current Q at the hot end??? Or is it that the very low capacitance coupling of your scope probe near the top of the coil means that it is equivalent to a constant current source, with current leading the voltage by 90 degrees (the capacitive reactance being many times the load impedance on the probe)??? ``````> Using the idea of I+Q current going into the cold end of the coil, I suggest > there are two tuning conditions of interest: > - when the antenna is tuned for maximum current out the hot end (into ``````the ``````> antenna wire), for maximum radiation, then the condition at the cold end is > not purely resistive > - when the loading coil is tuned so the current at the cold end is > resistive, the radiation current (hot end) may not be peaked. I checked this with great care. In my earlier e-mail I reported that the output waveform of the transmitter voltage was somewhat distorted due to harmonics. I now reduced the drive to the final amplifier to a level where the output voltage became a pure sinewave. The current into the bottom end of the coil was displayed as the voltage over a 0.78 ohm resistor ``````carrying ``````the current. I very carefully tuned the system for maximum aerial current. Because voltage at and current into the cold end of the coil were now both ``````sinewaves ``````I could superimpose them on the scope by varying the amplification in one ``````of ``````the two channels. The two sinewaves completely coincided, showing that maximum aerial current occurs when the impedance at the cold end of the ``````coil ``````is resistive. ``````OK, that point is cleared up. ``````I think I now have done the maximum that is within my measuring capabilities. But suggestions are still welcome. ``````Have you any comment on the 90 degree observation mentioned earlier? 73, Bob ZL2CA ```