TH78A.18

   Hello everybody! Recently I decided to check the performances of
 small "Duckie" antenna specified as T90-0444-XX in TH78 manual.
 I found that on 2 mtrs band this antenna, at first, has quite narrow
 bandwidth and, at second, tuned about 144.000 MHz or even some lower
 ( at the same time 70cm bandwidth seems to be enough...).
 Because of "integrated design" of this antenna it would be nonsence
 to cut the top end, so I tried to find another way to tune it to the
 middle of 2m band. At last, the problem has been successfully solved!
 So, you can easy tune the central frequency up to 147 MHz - just place
 a copper ring in the middle of conical surface of antenna ( between
 "OO"s as shown below ):

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  ³ÍÍ  ³          º     \ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
  ³ÍÍ  ³ K E N W OºO D   ³ dual band antenna           ³)
  ³ÍÍ  ³          º     /ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
  ÀÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÐÄÄÄ/
                  
               copper ring (about 13 mm internal diameter)

 The ring made of 0.3 mm wire gave me frequency shift from 144 to 145 MHz;
 if you need higher frequency, you should use wider ring ( about 4...5 mm
 for 147 MHz ) - you can solder it of thin copper.
    Don't use SWR meter for tuning! The best device is scanning scope or,
 at least, simplest RF field meter and your HT as VHF generator.
    That's all... 73, de Serge.
    RK3AXJ @RK3KP.MSK.RUS.EU      28-Aug-94