[TowerTalk] Rhombic vs. Yagi

[Tom Rauch]

> The former big Voice of America station in the U.S. used hugh rhombics.  I
> would say with their big bucks, they picked the best directional antennas
> that our money could buy.

Hi Ted,

The highest gain antennas they used were the USIA curtains.

They were much smaller than the Rhombics physically, and had 
more gain with a cleaner pattern.

Most later high-budget SW stations used curtains.

Rhombics are a good choice when wide bandwidth antennas are 
required and unlimited land is available. 

Factually, Rhombics have the lowest gain for pattern beamwidth of 
almost any directional array. They have the lowest gain per acre of 
space. 

The radiating efficiency of a normally terminated Rhombic (with a 
resistor rather than a recirculating device) is always less than 50%, 
and they gain limit (over earth) at about 3.3 to 4 WL per leg 
because it is impossible to force enough current into the outer 
portions away from the feedpoint, and because of all the minor 
lobes.

On the plus side they have very wide bandwidth ( when terminated)  
 and are simple designs. When a station has a small budget, a 
large land area, cares less about side lobes, lots of power, and 
operates over a wide frequency range Rhombics are a good choice.

But not for gain per acre or gain per beamwidth.


 
  
 
> 
> 
> 73, Aloha
> Ted Leaf, K6HI
> Kona, Hawaii
> <tleaf@hotmail.com>
> 
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73, Tom W8JI
w8ji@contesting.com

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