12m Beam Rebuild                                                      PAGE UNDER CONSTRUCTION  

The 12m beam has been a nice performer despite not being properly tuned.  With the bands improving thanks to a sunspot cycle (yea, what's that?) finally showing up at long last, the band has taken on a new level of importance. 

So while working on the various contest band rebuilds, this antenna is getting a bit of extra attenuation prior to this seasons big upcoming RTTY contests.

  

 Operation

The 12m elements share the dipole for the driven element.  Traps on the dipole resonate the antenna.  And adjacent elements provide the director function.  

  

  

  

 Models

Patterns for the two-element 12m beam are shown below.  Phase shifts of about 165 degrees are needed to clean up the F/B to this extent.  At the cost of low feed point impedance.  However, in the rebuild of the dipole center control board, a switched hairpin function has been included to assist.

For the 12m band operation, the 30m elements are best configured as a short.  But even shorted, they still have some significant amount of current.  This hurts the forward gain and the pattern shape.  

It may be possible to add some further decoupling to the 30m elements which would pay off in a bit better pattern for 12m.  But given the focus of the winter rebuilds (contest prep), this is a good interim result.

  

  

 

  

  

 Build Details

The 12m DE shares the role with the 80m and 160m dipoles.  A detailed explanation of the DE control board is found here.

The center control board looks like this - note it contains a RVM sensor which will be used in fine tuning the 12m beam elements.

  

  

Director function is provided by these simple end control boards. 

The default configuration is east-beaming (the east element relay is wired NC while the west element is wired NO).

Each board is equipped with RVM sensors.  And a SO-239 for easy MFJ-259 connection.

  

  

  Results

  

© 2011-2016 AC0C - All Rights Reserved

ACØC  

Created with the QTH.com SiteBuilder.