[Antennas] Simple Dipole Question

2002年10月24日 19:39:18 -0500

If you dont have any coax, use of ANY feedline that is an =
electrical multiple of a 1/2wave length will be ok (even ZIP cord!)
BUT for multiband use (and I forgot to mention this in my earlier
msg), your hook up is ok IF you get rid of the coax and run the
LL straight to a tuner with a balanced output...then you can use the
antenna on ALL bands (except maybe 160 and 80)...
BTW 468/f is the correct formula....you should always cut the antenna
for freq...if in the clear, etc ,there is no problem...if you are close
to the ground or in trees, the length will have to be trimmed or added
to make it resonant...BUT A RESONANT or properly cut antenna should not
be trimmed to bring the SWR into line...SWR is only an indicator of
your xmtr to feedline match...NOT how well the antenna radiates...
and an incorrectly cut antenna will change the pattern, etc..
So if you are in the clear and the ends are not near anything, =
cut the antenna to the proper length...and then raise or lower it to
affect SWR (and measure SWR at the antenna, NOT the xmtr if you can)
I noticed you said you made the LL longer and cut the antenna to make
the SWR lower...your narrowbanded SWR is due to the antenna not being
resonant now...make it the proper length then trim the FEED for best
SWR...and enjoy...but any change below 2:1 wont be noticed on the air!
(Just a little sage advice from a BC engineer and fellow ham! :)
Chris
WB5ITT
Kelley Shaddrick wrote:
> =

> Thanks to all for the replies, a whole host of information.
> =

> After some fiddling around with it, the antenna is now down to about 1.=
3:1
> or so at about 14.1 MHz going to 2.5 at 14.35 MHz. I shortened the ladd=
er
> line and lengthened the antenna a bit to get it there. Seems very narro=
w
> banded.
> =

> Anyway, why didn't I use coax? I didn't have any and there's no place
> locally to get any. I used what I had, a few feet of RG-8X and some lad=
der
> line. Sorry, no antenna anaylzer either in this end, maybe some day.
> =

> I'll probably rehang the antenna with coax, but it was an interesting
> experiment.
> =

> Thanks to all,
> =

> Kelley -- W=D8RK
> =

> ----- Original Message -----
> From: "Kelley Shaddrick" <[email protected]>
> To: <[email protected]>
> Sent: Thursday, October 24, 2002 2:24 PM
> Subject: [Antennas] Simple Dipole Question
> =

> > Today, with nothing better to do, I stuck up a dipole cut for 20m (14=
=2E2
> MHz)
> > using 468/frequency. It's strung between two trees at about 50 feet i=
n the
> > air. I fed it with ladder line (450 ohm) to the house (about 100 feet=
) to
> a
> > 1:1 balun and some RG-8X (about 20 feet) into the 2nd floor shack. Th=
e
> > initial swr reading is infinite across the band, no dip anywhere, not=
 even
> a
> > little. I suppose since I'm using ladder line, or window line, I need=
 to
> cut
> > things different. Any thoughts?
> >
> > Thanks,
> >
> > Kelley -- W=D8RK
> >
> > - - -
> >
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> - - -
> =

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