Hi Jim, Let me take a crack at this based on some online reading I just did, and the examples I found were based on treating the antenna as a transmission line (W8JI as well as others treat it this way). I would estimate the voltage at the tip of 1/4 wave vertical running 1500 watts to be 3437 Vrms = 4861 Vpeak. This is just an estimate using some general assumptions.
Full Details: The above assumes the feedpoint impedance is 35 ohms, and that the characteristic impedance of a single wire vertical acting as a transmission line is considered to be between 400 to 650 ohms (I used the average value of 525 ohms). Using 525 ohms as the characteristic impedance of the single wire vertical transmission line, this would translate into an impedance at the tip of the 1/4 wave wire to be 7875 ohms which appears to fall into the range of expected tip of antenna impedance values stated online (easy to transform the feedpoint impedance to the tip of the antenna since we are dealing with a 1/4 wavelength but you have to take a leap of faith that the characteristic impedance of the single wire antenna acting as a transmission line is 525 ohms). If you then treat the single wire vertical as a lossless transmission line, the voltage at the tip of the antenna calculates to be 3437 Vrms (4861 Volts Peak) when running 1500 watts. The online examples I saw were lacking a lot of detail, and some included some obvious errors. Therefore I had to take the best of each example to come up with my above approximation (assuming the online examples were on the right track). I hope others will step in and correct me if they feel I have not interpreted things correctly. I'm probably sticking my neck way out on this one :) 73, Don (wd8dsb) On Tue, Apr 16, 2019 at 8:38 AM Jim Miller <[email protected]> wrote: > Is there any data on what the voltage might be at the top of a full size > 80m vertical at 1500w input? > > Is there some zener like ionization at the top that limits the voltage? > > If so is there a way to estimate the voltage at lower points along the > vertical? I assume the scaling wouldn't be linear since starting at the > bottom on 36 ohms (sorta) and going to "infinity" at the top would preclude > that. > > Thanks > > jim ab3cv > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
