Just what is a balun?

[Paul]

The opportunity for using technical Geek Speak is overwhelming BUT here's a basic guide into the thingy called a balun.

First the word itself. Balun stands for BALanced to UNbalanced impedance.
Whoops, geek speak, sorry.

When you use a mobile or proper home base aerial, you normally won't have a problem. You know the type, standard Car CB whips or the long 3m (ish) metal poles on the side of a house.

Having said that, the homebase aerials sometimes won't SWR in nice and low down unless you use multiples of 3m of coax. This effect is caused by the radio waves "escaping" down the outside of coax which wreaks all the good work you were trying to do when SWRing in the aerial.
There is nothing wrong with the coax or aerial, it's just something that happens with radio waves. Weird isn't it?

Same thing in a car or unusual vehicle installation. Most CB aerial mounts come with a preset length of cable. THen into a van you go and you need a couple more feet of coax. Simple, you add a VERY LONG patch lead. Suddenly it's really hard to SWR in the aerial. Same effect. It's not the aerials fault or the patch lead, it's them damn radio waves escaping out of the coax.
THis also happens if the two connectors on the patch lead are bouncing off car bodywork so don't forget to wrap insulation tape round them thus keeping them insulated. Apart from that, the effect is easily cured by only use extension leads that are multiples of 3m.

So why bother with a Balun?
Good question as a simple cure is to keep your aerial coax in multiples of 3m. The problem is all us home base covert aerial installers making our own aerials and those who don't like meters of spare coax curled up in the boot of our car.
Without one, it causes the aerial to transmit it's signal PLUS a hotch potch mix of electrical gunk better known as television interference or TVI.
No good, not good at all as you'll probably upset someone and up you pop on the neghbourhood radar as being a trouble maker.

THey aren't huge complicated things and for the home base "player" fun to make. You can buy them. In CB shops they are sometimes called TVI filters. A little box that fits in the aerial lead.
What's in the box? A ferrite (Powered iron dust) ring with a couple of turns of wire round it and two sockets i.e. in and out. Just don't connect it up the wrong way round!!!!!!!!!!!!!!

When LS was talking about wire aerials for home use I added a bit about making a balun. Here is the link to a ham site that shows just how simple it is. http://www.hamuniverse.com/balun.html

Finally I'll wrap up by saying that a balun doesn't stop you needing to SWR in your aerial and to remind you that an aerial matching unit (AMU) a.k.a. Aerial tuning unit (ATU) might protect your rig but in some cases makes a badly tuned aerial radiate even more television interference (TVI).

For all you home based DIY aerial makers, fitting a balun is almost a given.

Paul

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Darn it, spotted an error. When buying a TVI filter from a CB shop just make sure that it is a 1:1 BALUN as some cheapie ones aren't and won't help you with long wire aerials.