Index Thread Archive Aug-2003 Archive Send
 Main index   Previous in threadNext in thread   Previous in archiveNext in archive   Index by Subject for Aug-2003Index by Author for Aug-2003Index by Date for Aug-2003   Index by Subject for ArchiveIndex by Author for ArchiveIndex by Date for Archive   Reply to messageNew message 

Subject: 40 meter relay box questions
Author: force12e <force12e@lightlink.com>
Date: 01-Aug-2003 10:13:53
re: Keith Dutson and 40 meter relay box question(s)

Good afternoon.

Several items to clarify here! If the original tuning was set for the driver
at 7.140, the reflector was probably (not stated so I am guessing here) set
at the manual-suggested 3-4" from the center support, which places the
reflector below the band (for CW operation). One relay box is typically used
to switch between CW and phone on the driver only. The reflector is left in
"CW mode." The antenna performs on CW like before and on phone it has gain,
but the pattern is obviously not as good (the reflector is tuned for CW -
way low from the phone band).

If the reflector is moved up to 7.140 in an attempt to accommodate both
modes, the antenna will reverse direction on CW. This is because the
reflector at 7.140 will be above the CW band and operate as a director, not
as a reflector. The directivity of a 2 element Yagi is determined by the
relationship of the parasitic element's frequency to the actual frequency of
operation. In general terms, if the parasitic element is higher than the
frequency of operation, it will act as a director. Likewise, if the
parasitic element is lower than the frequency of operation, it will act as a
reflector.

If one wants to optimize for both modes, a second relay box one can be used
in the reflector as well to track the driver frequency. Mechanically, this
does require the reflector to be retuned, as the relay box is being inserted
at the feed point.

The usual installation leaves the reflector set for CW and switches only the
driver, which keeps the transmitter/amplifier happy. There are some who
switch both elements, particularly if both relay boxes are done at
installation time. On our 80/75 meter Yagis, all elements have relay boxes,
as they are installed from the start.

73, Tom N6BT







--------------------------------------------
Force12Talk mailing list provided as a service by Force 12 Antennas, Inc.
Force12 Web Site: http://www.force12inc.com

To Submit Message to the List: Force12Talk@qth.com
To unsubscribe and view the Message Archive: see http://qth.com/force12/list
For problems with the list: contact force12@qth.com

This Thread
  Date   Author  
* 01-Aug-2003 force12e
This Author (Aug-2003)
  Subject   Date  
* 40 meter relay box questions 01-Aug-2003
Magnum 620/340? 31-Aug-2003