Feb 17, 2008
NVIS_backyard test version; 16:1 or 36:1 ?
For several weeks now I've been trying an NVIS type antenna in my backyard.
Actually it is simply an extremely low dipole 'cause that is all what would fit :)
I have tried a few setups using 2x 5mtrs copperclad steel wire in a flat shape @1m50 and later on top of a 4m fish-pole in an inv-vee shape. Such an electrical short antenna shows a pretty high reactance. I used a temporally setup to test a 16:1 and a 36:1 transformer, build by using a BN202 #73 binocular and teflon coated wire.
To minimize common mode effects by winding 14 turns RG58 on two type-J ferrites.
Results: although the 16:1 showed a much flatter SWR response on the Palstar antenna analyzer, the 36:1 version provided more output and better s/n results below 2MHz.
Surely a different length of the dipole would change the performance even more, but my backyard dictates otherwise. Rens PA3FGA build a 2x 7mtr version +36:1 x-former @1m70. So far his one seems to do a better job than mine, so I need to try some more.
3 weeks experimenting and listening on MW, 160mtrs and 80mtrs, comparing it to my other fixed 6m fishpole vertical antenna (tuned to 1830KHz) finally shows a clear winner in the 36:1 x-former.