Building an own "Stackmatch"


Nowdays lots of people are putting up antennas to either beam in different directions at the same time or just to stack them and get a lower angle of radiation. In both cases you need to somehow transform the two 50 ohm antennas so you still get 50 ohm output/input to the radio when you have them both connected. I have made a couple of these boxes and they are very simple to make. Some people simply just make stacking cables but I prefer using a UN-UN transformer since it works on several bands and takes much much less space.

The idea

A stacking system that is made this way is simply a aproximation of a two way stack and three way. The UN-UN transformer has got a ratio of 2.25:1 and that way you will get about 56 ohm with two 50 ohm antennas connected and 37.6 ohm with three antennas connected. That gives you a reasonable SWR in both cases.

Figure of the stackmatch
Picture 1. The idea of how a stackmatch works using a UN-UN transformer.

Making the UN-UN transformer

First of all you will need to have a core to wind the transformer around. I used a FT-240-61 core but anything with 125 in permeability or less works just fine (ex. FT-240-61). Wind it five turns trifilar around the core with copper emelded wire and connect the wires together as shown on the picture below.

Figure of the stackmatch
Picture 2. How to make the UN-UN transformer.

Before you mount the UN-UN transformer into a box you should test it out with some kind of dummyload. It is best if you have an antenna analyzer or network analyzer but it works to test it with a Tranceiver aswell. Just make sure to use a dummyload that handles the power if the later option is chosen. I used a network analyzer at school and just a few resistors when testing it.

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