> My question is regarding the feeding of the antenna, should it be > straight with 50 Ohm cable? Should I make some impedance transformer? > (I have FT240-61) that I could use.
Based on your description, I just ran your "T" in 4Nec2 with the NEC/4.2 engine. Your T should have a base Z near 21+j110 at 1825 kHz and will be resonant at 1620 kHz which will help to push the max current point up the vertical radiator and further away from the ground surface. Keep in mind that the base Z of a T will vary quite a bit depending on ground condition and number of radials deployed. The last 160m T I modeled for N4NN showed very close accuracy when compared to an N2PK VNA measurement after assembly. You could use an ATU back at the shack end. VSWR on the line near the base will be roughly 15:1. Use low-loss coax like LMR400 and total loss over 100 feet will be about 0.5 dB + tuner loss. VSWR at the tuner end, owing to line loss, will be about 12:1 in this example. *However*, depending on the exact line length, the Z at the tuner will be as high as 700 ohms, and as low as 4 ohms, so a high quality shack ATU will be important especially when line length results in a line input Z in the single digits. Not many commercial tuners do well on 160m with super low-Z terminations. Or, build a low-pass L network at the antenna base after measuring actual base Z. If it's near the 4Nec2 model, the L will consist of 14 uH series L and 1253 pF of shunt C across the base. Make them both variable if possible and use high Q parts to minimize loss. A variable L with a typical Q of 200 would result in 5.5 amps of coil current (ref. 1500 watts) and a total network loss of 0.09 dB + matched line loss. I would keep the input coaxial feedline on the ground or in the alternative, under the radials. Use a high-quality 1:1 ratio current-choke at the input to the L network. Paul, W9AC ----- Original Message ----- From: <[email protected]> To: <[email protected]> Sent: Wednesday, January 25, 2012 2:27 PM Subject: Topband: T Vertical feed > Hi Everyone, > > just finishing puting up a T Vertical (exactly in T shape) using 2 > supports at the ends. > > The vertical portion is 18m and the T is 17m to each side (34m total). > > I am laying radials from 20m - 40m (have about 20 right now). > > Thanks for help, getting ready here for CQ WW cw 160M. > > 73's Filipe CT1ILT aka CR6K > > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
