Hi everyone, thanks for the answers, I finished today laying down radials in a total of 48 that vary from 20m to 40m (tomorrow will add a few more).
I tuned the antenna and the final measurements of the antenna are 18m vertical + 14,5m to each side (29m). I measured the impedance at the base and it is Z = 23 + 9j with VSWR of 2 to 1. The VSWR after 50m of coaxial cable and a home made 1:1 balun (made with coax) is 1.7 to 1. I tried the antenna a few minutes ago and I worked a couple of European guys, will try later for USA. Tomorrow I might build some LC-Network to adjust the impedance. Thanks for help guys 73'S Filipe Lopes CT1ILT Citando Paul Christensen <[email protected]>: >> 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 > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
