```Hello Piotr, ```Again thanks for your work. The comparison of the 3 bands is very interesting. If i include the reduced antenna efficiency it is anyway an advantage to transmit on lower frequencies, at least below 2000 km. So, if the QRN situation @ the RX side on these 3 bands is about equal and if we think about the lower QRN on 46 km compared to 33 km, it could be shown that 46 km is a real alternative. What do you think when going over the alps? What might be better, 33km, 46km or 58 km? Your forecast please ;-) Maybe i can transmit in the 8th experiment with a DFCW shift of 2,5 kHz ;-) Means, the dash appears on 33km and the dot on 46km. So we could compare the S/N levels with negligible QRN changes within the transmissions... ```I am interested in your and other's ideas! 73, Stefan/DK7FC Am 05.10.2010 22:53, schrieb Piotr Mlynarski: ``````Stefan Schäfer pisze: ```The link to the IEEE paper is very interesting as well! Maybe the scientists over there are interested to take part on the experiments? Do you know some of them? Maybe we can combine the amateurs and the scientific work, although they will have no appreciation if i transmit "73" instead of a constant carrier ;-) PS: If you have the time, could you give us some ideas to compare 8970 Hz and 6470 Hz? Or even 5170 Hz if i can set up a 300m vertical? Maybe i should do the first test on 5170 Hz before you take the effort ;-) ```Stefan/DK7FC ``````Hello Stefan, VLF, ```you will find (attached) graph showing strength of E-field as a function of distance calculated for that three frequencies i.e. 8970,6470,5170 Hz. At this range of frequencies going down with its values indeed gives an increase in the field strength but what is not displayed here is a rapid attenuation of the field strength if one goes further down with frequency thus approaching so called cutoff frequency which is defined as fc = velocity of light/(2 * ionosphere height); say, h = 80 km so fc = 1.88 kHz ; h = 70 km so fc = 2.14 kHz etc... ```(within the used propagation model of an earth-ionosphere waveguide ) The present numerical values were calculated using your 7th setup i.e. ant I = 1A, length =200meters. i took only one height = 80 km ```according to the IEEE paper.. no, i do not know its authors - it was just found ( and saved :) ) during my literature search. 73, Piotr, sq7mpj ```qth: Lodz /jo91rs/ ```