[Antennas] Simple Dipole Question

2002年10月24日 22:01:48 +0000

You need to change the LL length if you want to use it as you have it set=20
up. All is good except the LL length.
If you change it so that it is some multiple of an electrical=20
half-wavelength ( one-half, two halfs, three-halfs, etc), it will work and=
=20
your SWR will drop to a normal value. I don't know the length you need in=20
feet - the velocity factor of the line must be considered. You could guess=
=20
the velocity factor is somewhere around 0.9 and calculate a starting=20
guesstimate, cut to that and be prepared to lengthen/shorten it a bit to=20
"tune" it.
What is happening right now is the LL is acting as a transformer to change=
=20
the dipoles feed impedance into some random value that yields a high SWR at=
=20
your rig. Changing the length to exactly a half-wave multiple will stop=
 that.
Good luck
Jerry W4UK
At 14:24 10/24/02 -0500, Kelley Shaddrick wrote:
>Today, with nothing better to do, I stuck up a dipole cut for 20m (14.2=
 MHz)
>using 468/frequency. It's strung between two trees at about 50 feet in 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. The
>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