The Channel Master 4221  4-Bay





The CM 4221 is also known as the 3021.


This is a top performing medium range antenna:  Lots of gain but not very directional.  Typically it is used in the 20-35 mile range.  It is good at rejecting multi-path from the rear.  But multi-path usually doesn’t come from the rear, so this is not usually a good antenna for multi-path.  If you want to avoid the hassle of a rotor, consider this antenna.


A new version of this antenna is being introduced and should be available late in 2008.  The new version looks lighter.


Antenna builders:


I am amazed at how many people want to build this antenna.  Pictures of several handmade versions can be found on the web.  In the process of simulating it I discovered it is mathematically a rather complicated antenna.  Adjusting it experimentally is not practical.  For example if you adjust the screen-dipole spacing, it appears that the gain changes a lot, but in fact it is mainly the terminal impedance that is changing.  It might be practical to adjust it for your weakest station.  But unless you have modeling software and a good model, the best overall strategy for you is to copy a known good design.  The 4221 dimensions are:


      Length of dipole element wire = 7.8” x 2

      Dipole vertical separation = 8.0”

      Screen-dipole separation = 4.5”

      Feed bus wire separation = 1.2”

      Feed bus wire diameter = 0.100”


The Feed bus is a transmission line and its separation/diameter ratio determines its characteristic impedance.  The ARRL Antenna Book is an excellent reference for all antenna builders.







This page is part of “An HDTV Primer”, which starts at    www.hdtvprimer.com