Message:21439 In: TECH.WW
From: G8MNYDate: Mon, 27 Apr 26 06:36:00 Z
Newsgroups: TECH.WW
Subject: Band2 6el Narrowband Yagi
Message-ID: <58226_GB7CIP>
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From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Corrected Feb 13)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Well I finally got around to it, I re-designed the large 6el broadband beam I
previously made, using the MMANA-GAL program (CD 2010 RSGB yearbook & online).
My community radio station SUSY RADIO I do the engineering for, is too far away
to hear at my QTH for a normal small aerial. Orginally I wanted the aerial to
do the whole 20MHz of UK's Band2 87.5-108MHz. But that was a mistake, as at my
QTH I have strong QRM of the back of the aerial, so I re-optimised the design
for best front to back ratio on just the one frequency of 103.4MHz.
2x
717 4x
³mm 640
³ Ú¿mm 2x 2x
³ ³³ 623 2x 620 2x
³ ³³ ³mm 601 ³mm 596
³ ³³ ³ ³mm ³ ³mm
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³ ³ ³
ÃÄÄÄÄÄÄÅ0ÄÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´
³ 353 ³³ 477 ³271³ 796 ³ 741 ³
³ mm ³³ mm ³ mm³ mm ³ mm ³
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³ ³ ³
³ ³³ ³ ³
³ ³³ \ /
³ ÀÙ Strange lengths!
³ 80mm dia Elements Ally tube 20mm dia.
folded ends.
POLAR DIAGRAM
_-~~~-_ 8.54dBd
/ \
Þ Ý
Þ Ý
\ /
\_ _/
>ú<
< >
~-~
AERIAL IMPEDANCE
This is a good 75 Ohm balanced on the design frequency, so just a 1/4 wave coax
choke balun is needed in the coax feeding the connection box.
SWR 75ê .===========================.
³~-._ (( Folded Dipole ))
20´ '~-..__ '=========(0) (0)========='
³ ~~-. \ / _ _ _
10´ '. COAX CHOKE³ ³_/ \/ \/ \____
³ ú. _..- 1:1 BALUN ÀÄo)_/\_/\_/\coax
1Å '--'' Just under 1/4 wave of coax~~~~
87.5 92.5 97.5 102.5 107.5MHz coiled up (3-4 turns) near
the connection box.
R ê X ê
150´ 250´
³-._ ³ _.-'
100´ ~-. __ 0´ _.-'~
³ ~-. __..--'' ''- ³ _.-'~
50´ '-.-'' -250´ _..-~
³ ³ _..-'
0´ -500´..-'
87.5 92.5 97.5 102.5 107.5MHz 87.5 92.5 97.5 102.5 107.5MHz
GAIN dBd F/B dB
12´ 40´
³ ...- ³
9´ ..--''' 20´ .--''-..__.
³ -' ³ ,-''~
6´ __..--._.' 10´~~--._..--''
³.--'' ³
3´ 5´
87.5 92.5 97.5 102.5 107.5MHz 87.5 92.5 97.5 102.5 107.5MHz
IN USE
This works well on 103.4MHz. I can now hear my SUSY RADIO station with very
little QRM. Gain about 2dB better than the broadband version & F/B ratio 22dB
not 11dB.
See My Tech Bul "Band2 6el Broadband Yagi", "Coiled Coax Choke Balun for VHF",
& "FM Stereo QRM".
Why don't U send out an interesting bul?
73 De John, G8MNY @ GB7CIP
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