I have been working for weeks on my antenna system.   Today, October 3rd, 2006, I finished upgrading the USA Rhombic with a direction switching relay box controlled from the shack.

The control line is 1,000 meters long and is tied to a messenger steel wire between poles of the feedline run at 2 meters height.  

I run 220 VAC out to the site and use a Wall Mart 12VDC transformer to switch the relays.

 This gives me the ability to switch the USA rhombic between short path and long path and effectively adds another Diamond to my arsenal. 

Initial test are very gratifying,  US stations go from S9 to completely inaudible when I switch directions!

 The image below shows the circuit I use to switch directions (tnx ZL6QH!)

The picture below shows the main lobes of my three Diamonds, the 3DB beamwidth is around 20 degrees and there are numerous sidelobes that fill in the gaps, for example the main USA direction is good into YV5 and CE which are inaudible on the reverse direction of the JA Rhombic. 

Obviously there are gaps in the coverage, but the directions chosen target the main HAM populations.   Note that the EU direction of 110 degrees covers W6, W7 Long Path as well.

I will be building more Diamonds to fill in the gaps in the coming years. 

From: Theory and application of antenna arrays

by M. T. Ma

Senior Member of the Technical Staff

Institute for Telecommunications Sciences

Office of Telecommunications

U.S. Department of Commerce

Boulder, Colorado

 and

 Professor-Adjoint of Electrical Engineering

University of Colorado

6.2 Sloping Rhombic Antenna

Since the rhombic was first introduced by Bruce, (7,8) it has been extensively used for short-wave communications.  The antenna consists of four straight wires of the same length l arranged in the form of a rhombus.  It can be considered as an extension of the vee antenna studied in the previous section.

References:

7.  Bruce, E,  Developments in short-wave directive antennas, Proc. IRE, Vol. 19, No 8, pp. 1406-1433, August, 1931 

8.  Bruce, E., A.C. Beck, and L.R. Lowry.   Horizontal rhombic antennas,  Proc. IRE, Vol. 23, No. 1, pp. 24-46, January, 1935

The references also quote:

10.  LaPort, E. A.  and A.C. Veldhuis.   Improved antennas of the rhombic class,  RCA Rev., Vol. 21. No 1, pp.117-123, January, 1960

If anyone has access to these references, I would be most grateful for a copy, especially of reference 10.

I understand that Bruce hoped that the Rhombic would bear his name and that initially the antennas were called Diamond antennas.