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 <w9ac@arrl.net>:
>> 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: <ct1ilt@sapo.pt>
> To: <topband@contesting.com>
> 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
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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