Hi Rod, ever been to Skelton ? here you will find the tallest lattice mast in the UK, 1200 ft, It is a giant VLF umbrella transmitting to subs on 22 khz. You can get fairly close to it and even get right up to where one of the umbrella wires lands at quite a shallow angle. At that point the mast itself still looks quite a way off. Not too far away you'll find Anthorn where there is another VLF umbrella used for a similar purpose also the national MSF time sig on 60 khz. you cant get anywhere near that one. Not sure what Matt is proposing to use but engineering wise, if you have the space, an umbrella would seem the best option for max efficiency without having to build a tower thats half way to the moon.