The AM Forum

Years ago you’d put up a dipole and everyone seemed happy. Occasionally you’d hear about someone using one of the original W2AU baluns. I’ve noticed that over the past few years baluns are being touted as the magical cure all for a variety of possible problems. I’ve been seeing several companies selling 1:1 baluns which are basically several turns of coax wound around a ferrite core. I’ve used this technique to get rid of RF on the coax, but I’ve never noticed any “noise reduction” that most of these product claim to offer.

Have any of you ever experienced any noise reduction? 

It probably comes down to this:

Any antenna has a certain radiation pattern. It may be a figure eight like a dipole, a unidirectional pattern like a Yagi - it could be mostly vertically or horizontally polarized, etc.

Since the antenna doesn't know the difference between unwanted noise and real desired radio signals, it cannot differentiate between the two. So it will pick up local power line or house noise in the neighborhood depending on it's pattern and proximity.

Now, what can upset a good antenna is feedline radiation from an unbalanced feedline that does not cancel and creates new and unwanted lobes. These unwanted lobes may be closer to noise in the house, more vertically polarized to pick up powerline noise, etc.

The bottom line is if one of these baluns can effectively reduce feedline radiation by choking off shield currents or helping to balance the feedline, in a partuclar situation, it may reduce noise by reducing unwanted lobes. However, if the antenna already has a good feedline match and balance, it will probably have little effect.

Much will depend on where the unwanted noise is coming from and its proximity. You just have to try it an see. It's like rotating a Yagi on 6 or 10M and seeing the S meter go up and down based on where the local noise is coming from. The feedline radiation is more fixed and it will be pot luck of what you hear.

Do whatever it takes to reduce feedline radiation and beam the antenna pattern away from the noise source and everything will be optimized.

Personally, I always use a balun on all of my Yagis as well as dipoles. The Yagi baluns are usually 4:1 step down transformer type using a primary and secondary at the feedpoint. (actually unbalanced to balanced)   The higher band dipoles use a simple bunch of coax turns on a 6" PVC pipe (choke)and placed at the feed point. The lower band dipoles use a hank of coax (choke) at the feed point.

Usually the higher the frequency and more directive the antenna (Yagi or a stack) the more important and critical the balun requirement.

BTW, a  fully modulated KW carrier of AM can smoke one of those W2AU ferrite core baluns.    Also, nearby lightning strikes can permanently saturate the core.  If the swr suddenly soars, you will know... ;)

T

Yes, I have had quite helpful effects from using baluns, chokes/isolators.

-Used at the antenna end they help keep RF on the antenna and off the feedline.  This maintains optimum antenna pattern by preventing the feedline from radiating.   It also prevents feedline 'common mode' noise pickup from local RFI sources.

-An 1:1 isolator close to the radio also will decrease feedline common mode noise pickup.  For those working low bands (especially the coming 630m and 2200m  bands) and sensitive digital modes.

As a townhouse dweller, adding them at both ends has significantly decreased the noise from my 200 neighbors!

I use two 85 foot wire loops that are 100 to 150 feet away from the house for nice quiet reception from the AM broadcast band through 40 meters. One of them is oriented for north-south reception and the other for east-west reception. Each loop has a 9:1 balun at the feedpoint and a 1:1 balun at the RX antenna input of each rig. If I eliminate the 9:1 balun at the feedpoint, the directional characteristics fall apart and some noise begins to creep in. If I eliminate the 1:1 transformer at the RX input of any rig the SNR of these antennas is seriously degraded. I'm pretty sure eliminating the transformers at either end makes the antennas very susceptible to noise that collects on the outside shield of the RG-6 feed lines. At any rate, they work well for me!

Rob W1AEX

I've been using those particular baluns for decades with satisfactory results.

Al

Thanks for all the feedback. No doubt they work very well for keeping RF out of the shack. I proved this when I first started using Flex 5000. I tried two different 1:1 baluns (one I made and one I bought) hoping to realize some reduction in man made noise. Personally I doubted it would have any improvement but with so many people talking about it I figured I'd try it. Absolutely no difference switching it in or our over a 1 month period on various types of noise.

I'm really wondering if the improvement some people claim is attributed to the "monster cable" syndrome? You buy these cables for $100 and convince your self it sounds better! Hey, after I wash and wax my car, it definitely rides better!

If your noise source is being directly picked up your antenna a 1:1 balun won't make any difference at all. However, if your antennas are away from noise sources and you have long runs of coax from the feedpoint to your station equipment all kinds of noise may be picked up on the outside of the shield. This common mode noise is where the isolation of "braid breaking" offered by a transformer at the feedpoint and in the station can make a big difference. The picture below shows one of my 9:1 transformers used at the feedpoint of one of my 85 foot wire loops and the 1:1 transformers at the station equipment use the same kind of construction with an equal number of turns on the primary and secondary.

Rob W1AEX

In my case it's not imaginary, it' not a placebo effect.

This winter I installed a new 1:1 balun from Radio Works on a new antenna installation and setup an A/B configuration with a switch.  I used a spectrum analysis program to target and measure specific noise problems.   The difference was clearcut as could be.  Then I added as second 1:1 isolator just before the antenna, and saw more improvement.

Maybe it doesn't make much difference if you are in a low noise evironment.  I believe the problems are more noticeable for digital work and low bands.