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G8MNY  > TECH     13.05.22 07:07z 96 Lines 4160 Bytes #25 (0) @ WW
BID : 21576_GB7CIP
Subj: Band2 6el Narrowband Yagi
Path: SP7YDD<SR1BSZ<IW0QNL<ON0AR<GB7CIP
Sent: 220513/0703Z @:GB7CIP.#32.GBR.EURO #:21576 [Caterham Surrey GBR]
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
 mm    640
       ڿmm    2x                  2x
            623    2x            620              2x
              mm 601             mm            596
                 mm                            mm
                                               
                                               
                                               
                                               
                                               
 0Ĵ
   353   477  271       796            741     
    mm    mm   mm        mm             mm     
                                               
                                               
                                               
                                               
                                 
               \ /
          Strange lengths!
     80mm dia     Elements Ally tube 20mm dia.
     folded ends.

POLAR DIAGRAM
               _-~~~-_ 8.54dBd
              /       \
                      
                      
              \       /
               \_   _/
                 ><
                <   >
                 ~-~
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 75                                    .===========================.
   ~-._                                  (( Folded            Dipole  ))
 20    '~-..__                            '=========(0)   (0)========='
              ~~-.                                     \ /  _  _  _
 10               '.                         COAX CHOKE _/ \/ \/ \____
                    .     _..-              1:1 BALUN o)_/\_/\_/\coax
  1                   '--''               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                                     X 
150                                   250
   -._                                                           _.-'
100   ~-.                 __            0                   _.-'~
         ~-.      __..--''  ''-                        _.-'~
 50         '-.-''                   -250         _..-~ 
                                             _..-'
  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
                           ...-          
  9                 ..--'''            20                 .--''-..__.
                  -'                                 ,-''~
  6     __..--._.'                     10~~--._..--''
   .--''                                 
  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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