New Channel Master CM 3671 Antenna Modification  July 2011

   This modification is an attempt to improve the UHF gain of this antenna, and perhaps also VHF to some extent.  I've always felt uneasy with how combination antennas simply join the VHF log periodic section with the UHF yagi section via a pair of simple metal rods.  I can't help but imagine several dB's worth of UHF signals being sucked up by those rods being attached.

    The solution ... which I used on a smaller CM used in Brampton, ON ... was to separate the VHF and UHF feeds, using the last VHF dipole as a feed, and the existing "combo" feed (really just the UHF bowtie) as the UHF feed.  The following is shown for illustration purposes only.  This modification is not endorsed and if you do so, it is done at your own risk.


   COMBINER RODS...
     First job was to snip the new CM 3671's VHF-UHF combiner rods off near their riveted (VHF) ends...leaving small stubs left.





   THE MODIFICATION...
     The remaining combiner stubs
hammered flat to allow bolts to be attached...
      A
ttached to a balun as a VHF feed...
     The UHF bowtie (the original feedpoint) is now a stand-alone UHF feed...
      VHF unamplified...  UHF goes through a Winegard AP-4700 19 dB UHF-only preamp...



   ANOTHER VIEW...
     With the elements opened up...





   AND ANOTHER VIEW...
    Note that the director sits atop the boom and does not touch the combiner stubs...




   AND UP IT GOES...
 
  The new CM 3671 on bottom for horizontally-polarized signals...TV, FM, AIR band ...
    a new Create CLP 5130-2 on top for verically-polarized signals... WB, PSB & some AIR band.
    Rotor is a new Yaesu G-800DXA... after going through 3 rotors in 6 years, it was time for an upgrade!




READY FOR DX...
  Awesome results.  UHF gain much better.  VHF improved too (lower noise floor ... especially
  in 108-112 MHz VOR band).





THE WARM FRIENDLY GLOW...
   Of the Yaesu control box. Reminds me of an aviation dial...
    The blue glow below is from the Zenith DTV box...




THE END...
  
  William Hepburn
   Grimsby, ON, CAN  2011.

THE END...