Magnetic baluns ... less noise?

[NRD-345]

I recently read comments in another forum that stated magnetic baluns are useless. (Compared to WHAT, I would ask.)  Of course, there are all kinds of variables when comparing different antenna set-ups, but I live in a metro environment where man-made noise is prevalent, and using a magnetic balun on my random wire antenna has made ALL the difference in greatly reducing noise.  If your antenna of choice is a random wire, I highly recommend feeding it with a magnetic balun and 50 ohm coax.  In my experience, it's a simple installation that produces excellent results. I'd be interested in hearing from other SWL's about their experiences using magnetic baluns, pro or con.   
-With regard to signal-to-noise radio, I have noticed that using an external tuner certainly improved Signals, but also increased the Noise with it, resulting in no improvement of S/N ratio. It was a very interesting experiment. Thanks for the reply.

[RobRich]

I suspect your "magnetic" balun is likely rated for a 9:1 impedance transformation, correct? Given a longwire antenna can present a wide variance of impedance, including impedance ratings from hundreds to likely well into the thousands of ohms, the 9:1 transformer is improving the match to your comparatively low-impedance coaxial feedline and receiver at many frequencies. The other typical benefit is increased common mode isolation between the antenna and feedline.

The end result? Probably better signal transfer and hopefully less noise between your high-impedance longwire antenna and low-impedance receiver.

As for an "useless" situation, there can be scenarios where a 9:1 balun could be undesired or even detrimental, such as using one at the feed point of an already rather low-impedance antenna where a 1:1 current balun (or even direct feed) might be preferred.

Also in regards to an "useless" situation, the actual signal-to-noise might change very little with a balun if for example common mode noise is not an issue, even if the the signal is measured "stronger" at the receiver with the balun installed. S/N is a ratio, and assuming enough S already is available for reception, further increasing S can mean little if N is being increased by the same number as well - the ratio remains the same, so the result is little more than a change in the receiver volume setting for the listener.

On a personal note, awhile back I removed the 1:1 current balun at the feed point of my ground-level 148' coaxial "shielded" loop with no casually discernible S/N change. The antenna being a loop is already is decently balanced, and I have muliple snap-on ferrites along the coax feedline for some common mode isolation, plus a 1:1 common-code choke inside near the attached receiver. If it was being used as a monoband antenna, I might work out the model for a balun to better match the antenna to the feedline, but the impedance readings are "all over the place" anyway as I routinely use the antenna for general reception of longwave, mediumwave, and HF through ~15MHz.

[pendulous]

I purchased a couple and have used them on long wires. I really didn't notice a difference. however, there are so many variable my results do not mean much. My location is probably a bit quieter than most. that said, from the research I have done, the best way to reduce noise and improve rx antenna performance is to eliminate common mode currents. The best way to do this is common mode chokes. Many shortwave and in particular mw listeners will also use some sort of balanced feed lines which i believe are inherently more immune to common mode currents versus unbalanced coax. Google search Dallas Lankford and Tom rauch. both and others have done much research and experimenting on this.

[Josh]

One of the nice things about certain voltage type baluns is they can bleed off static due to all ports being at dc continuity, wich may lead to quieter listening and reduced chances of static popping any solid state electronics. Also, balanced line is prone to picking up and emitting rfi, coax is less susceptible especially if one employs ferrites on said coax.