Power Couplers – Broadside

ON4UN’s Low-Band DXing: Antennas, Equipment and Techniques for DXcitement on 160, 80 and 40 Meters [With CDROM]


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A power coupler in this example is a device that allows equal splitting of power from the feeder to the antenna’s in an array, many VHFDXers will be familiar with the theory but for HF people its a bit of a leap into the unknown, bear with me, and I will explain in full.

Firstly when you look at a power coupler for VHF upwards you basically get a box with the correct number of N Sockets for your application (1 in 2 out, 1 in 4 out, 1 in 8 out etc) in example One we can see one configured for one input and eights outputs. the distance between the input and the output is approx 1/4λ between the Hot pins, when adding to the outputs an extra 1/4λ feeder you end up with a 1/4λ split. So whilst on VHF

 

8 Way broadside array splitter

Example One: 8 Way broadside array splitter

So how does a broadside coupler work? Simply put when feeding antenna’s in Series, your EM field becomes out of phase, so you need to make sure that each antenna is within the same phase as the first. If you consider a VHF array it often comprises of Bayed and Stacked antenna’s, But when you get onto HF arrays, having bayed and stacked whilst possible would be an engineering nightmare, but for us in the UK a physical impossibility, due to Garden space and planning regulations.

If you see my page on 1/4λ verticals for HF, you will understand how to build them. Building a phasing harness is quite simple, what you have to remember is the further away from the original frequency designed for the more lossy your phasing will be, just the same as a vertical cut to a frequency.

The common way of doing this for HF is to use a length of feeder, with a T Junction at the end, followed by Two or More 1/4λ 75Ω feeders to the antennas.

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