>Hello,
>I would like to speak with anyone running a unipole on 160M.
Glen
I'm using a Unipole for almost 4 years; it is a very good antenna. The cage
helps to detune the tower during RX, without that my RX antennas just don't
work at all. The cage is grounded at the top and opened at the bottom, I did
not understand you comments about resonance.
You can check my Unipole at:
http://www.n4is.com/unipole/unipole.html
The tuning can be very easy. First I used a 4:1 balun and a series
capacitor. Because the antenna is electrical longer then 90 degree, the
system tuned that way is very , very broadband, 1:1,5 at 1800 and 1:1,5 at
1900 KHz flat most of the band. Lately I'm using a T match with 800pF series
a shunt inductor around 12uH and another series capacitor around 500 pF,
with this tuner the antenna has a incredible broad band 1:1,10 at 1800 and
1:1,10 at 1900 and flat most of the band.
Choke and ground all cables at the base is a "MUST". It means a capital
must.
The issue is 80, 40 and up, for 80 I have 3 vacuum relay to open the cage
around 75 ft, them using a L network I can tune the cage as a 1/4 wave long
for 80m. The same relay is open for 40m and I tuned the antenna as a 1/2
wave, this configurations has very narrow BW and does not work very well.
Also the BW is not good on 80 m either; I need to tune 3.5 and 3.8 with
different capacitor and same inductor with a tape.
I'm planning to feed it with a 200 ohms 4:1 balun using a counterpoise like
the R5 R7 half wave verticals. This configuration should result in a better
BW.
Regards
Jose Carlos
N4IS
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|