Topband: 160 inv L with two swr dip.

[George & Marijke Guerin]

Hi Jon,
    My first guess is that the impedance of the inverted L at resonance is
well below 50 ohms...  maybe at 1870 Khz?  Maybe 25 ohms.  Try a 2:1 UnUn
from Jerry Sevick's book and see if that helps.  I would think you may have
coupling to get the high dip, and you may see some combination of R + Xj
that gives you close to 50 ohms to give you the low dip at 1808 Khz.
    It is usually very difficult to gamma or omega feed a tower and work out
phasing.  I cannot comment.
    The tower with the 10 meter beam is probably still less than 1/4
wavelength if shunt fed.  In your case it is probably easier to work with an
L-net tuner or an UnUn to get the impedance you want at the inverted-L feed
point.
    Another matching system is to make the inverted L about 7 - 8 feet
longer than theoretical, and put a capacitor across it to bring the feed
point up to 50 ohms.  Then the wire is about 2 uHy inductance as part of an
L-network.
    Good luck        George        k8GG

----- Original Message -----
From: "Jon Dam" <jon-dam@post.olivant.fo>
To: <topband@contesting.com>
Sent: Wednesday, April 03, 2002 7:31 PM
Subject: Topband: 160 inv L with two swr dip.


> Hi all and tnx for a very nice reflector with a lot of very usefull
information.
> At our club we have 3 tower in  triangle spaced abt. 64,5 feet apart. # 1
is 60 ' + pipe and a 6 el 6m yagi.
>  # 2 is 74 ' + pipe & 5 el Telrex 10m yagi.
>  # 3 is 74 '  + pipe & 1/2  20m dipol  left from a broken 5 el Telrex yagi
( destroyed by wind ).
>
> I have put up a 1/4 inv L ( total lengt is abt. 127,5 ' ) on tower # 2
abt. 73 ' vertical, spaced 3,2 ' from tower, and 54,5 ' horizontal to tower
# 3.
> Use abt. 80 ' of  RG 17, and a direct feed to inv L  at base of tower +
abt. 70 radials 50 - 80 feet long .
> All radials are on ground, and it is solid rock.
> Base of tower # 2 is only 100 ' from ocean.
>
> With this setup I get two swr dip first is 1,4 on 1,808   ( 1,750
2,0 -1,808 1,4 - 1,870 2,0  ) 2 th dip a very low one  1,1 on  2,335   (
2,260 2,0 - 2,335 1,1 - 2,400 2,0 ) why is this so ??
>
> Is there one dip for the wire L, and a 2 th dip for the tower + top load ?
>
> Will I get a better antenna if I gamma feed tower # 2 with the 10 m yagi
top load ?
>
> Can I  Gamma feed two or tree tower, and then phase them with this 64,5 '
spacing on 160 m.
>
> I appreciate any help .
> vy 73 Jon, OY9JD
>
>
>
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