Sunday, February 24, 2019

Exploring balanced antenna couplers

Almost all the HF transceivers hams use cover 9 or more bands. It would be nice if our antennas did the same, especially if we don't have room for a massive antenna farm. One of the simplest antennas that does just that is the tuned feeder doublet. You put up a wire between two supports and run some open wire feedline down to the transceiver.

Provided it's longer than about 3/8 wavelength end to end on the lowest operating frequency it will perform well without much loss. Yes, you do get some funny radiation patterns with narrow lobes and nulls on higher bands, but you will be on the air. And if that worries you it's not to hard to put up another antenna for more predictable performance on a band like 10 metres.

There's only two problems with that. First of all the balanced feedline. You may have to make it yourself. Don't worry, we covered feedlines just over a week ago.

Then there's the antenna coupler. Some people feed tuned feeder doublets with a regular unbalanced antenna coupler and a 4:1 balun connected to its output. Yes that will 'work'. But it's not the most consistent arrangement and there may be significantly increased losses on some frequencies.

The solution is to use a balanced antenna coupler. These are not that common commercially. But you can build your own.  Some good ideas are presented below.

Link coupled antenna tuners Some ideas from W4RNL
Wide range balanced antenna tuner by W5JXM
QRP balanced antenna tuner by OZ1BXM
Symmetrical matchboxes many ideas from DJ0IP
W4MMQ Legacy balanced antenna tuner Very simple!
A balanced antenna coupler and multiband dipole One of my videos

Inductors can be made at home. But you will likely need to shop around for the variable capacitors required, most likely at hamfests.

PS: The items below may assist your experiments.  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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