Thursday, April 25, 2019

Some rhombic ideas

You can go through your whole amateur life without ever hearing a station using one. At least on HF, they require you to own a farm to fit them in. They need four masts to the yagi's one. And their radiation pattern is not easily steerable.

I'm talking about the rhombic antenna. Commonly found in older antenna books, they have utility if you have a lot of land and are mainly interested in one direction. Plus they are broadbanded and low noise on receive. If you've inherited some large rolls of wire and have room to string it up, then the rhombic might be your friend.

As the name suggests, the rhombic is rhombus shaped. Like a square but pushed over. It's fed at one end with balanced line. At the other end is a terminating resistor. This enables it to be directional, like a beam. The sides are several wavelengths long. For this reason they are made of wire.  Beam-like gain is possible if your rhombic is big enough and the angles are right.

If you're intrigued by all this it's cheapest to experiment with rhombics on the higher VHF or UHF bands. At least on UHF you may be able to mount it on a timber frame and turn it like a beam.

Some rhombic ideas are here:

* W8JI's rhombic write-up
* KB1SB's rhombic pages
* Joby's rhombic ranch
* Royal Aircraft Establishment rhombic design guide
* Dave Casler's Mighty Rhombic video
* Rhombic designs for UHF and microwaves

PS: Want some practical antenna ideas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


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