Google has a new service where it is possible to search through more than 7 million patents.   The data is stored on Google servers and is in the public domain.  

Below is the original patent application by Edmond Bruce for the Rhombic Antenna. 

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From:  A.E. Harper's book "Rhombic Antenna Design"

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VK0JLX operates from Davis Base in Antarctica.  The base uses rhombics for HF comms.  

Davis Base Webcam. 

This is a very professional and expensive installation.   They seem to feed all the rhombics from a central mast.   This was not possible at my location due to the terrain.

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The Rhombic

Early difficulties of terminating a wire high in the air led to the development of the rhombic aerial in which a second V is added, so that the ends can be brought together.  The same lobe addition principle is used but there is an additional complication, because the lobes from the front and rear halves must also add in phase at the required elevation angle.  This introduces a extra degree of control in the design so that considerable variation of pattern can be obtained by choosing various apex angles and increased gain above ground.

The rhombic aerial gives an increased gain but takes up a lot of room and requires an extra support.  There are two forms of the rhombic; the resonant rhombic which exhibits a bi-directional pattern and the terminated rhombic which is non-resonant and unidirectional.

The terminating resistance absorbs noise and interference coming from the back direction as well as transmitter power which would otherwise be radiated backwards; this means that it improves signal-to-noise ratio by up to 3 dB without affecting signals transmitted in the wanted direction.

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. 

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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.    

Here are some dimensions for the construction of Rhombic antennas  taken from the War Department Technical Manual TM 11-2617 “Antenna Kit for Rhombic Transmitting Antenna” .

This manual is available on CD on eBay.

A larger image may be downloaded from here . 

I do have design data for Rhombics up to 1000′ leg lengths but that data does not include pole spacings.

100 foot poles should be set 12 feet in the ground.   My end poles are 80 footers and are set down 8 feet with an additional 10 feet of dirt piled up around the bases.  They are then guyed with steel guy wires every 120 degrees on two levels – middle of pole and at the top.

I use #8 Hard Drawn copper for my USA Rhombic, and #10 CopperWeld for my smaller Rhombics.  I have also purchased 2,200lbs of #9 AlumoWeld antenna wire for my future projects.  The AlumoWeld wire has a breaking strength of 2000lbs.

Edmund LaPort’s “Radio Antenna Engineering” is a fantastic resource when constructing wire antennas.   The book can be downloaded in electronic form from LULU.COM and also from this alternative site .   It can also be downloaded from my site.   Please right click on this link to download the book (38MB) – courtesy of Dave Platt, AE6EO

A.E. Harper’s Rhombic Antenna Design is available from AstroLogos Books

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