Quiet Antennas? ? ? ? ? ? ?

(1/6) > >>

What are some low noise wire antennas? I'm mainly looking for something that is useful over most of hf, with a tuner or without.

I know that the terminated folded dipole is great at killing man made noise, but ive also heard that the resistors eat up most of your transmit.

Alternatives for low noise/multi band?   What about the buxcomm windoms?

Mike Waters:
If you have room, a Beverage antenna. Period. One wavelength long on the lowest desired band.

If you don't have room for a Beverage, then a K9AY loop (http://www.hard-core-dx.com/nordicdx/antenna/loop/k9ay/) or better yet, an array of 4 short phased verticals.

73 Mike

I dont have room for a loop :-/   I thought that a beverage antenna was only good for recieve?

First things first.  Noise is a signal.  Many people have "theories" about what makes a "quiet antenna" that are just plain wrong.  They do experiments with a new type of antenna, find that it's "quieter" in some general way and fall in love with it, and chalk up the "quietness" to all kinds of fancy sounding radio jargon, when the real answer probably doesn't have anything at all to do with electromagnetic radiation of any kind.  A terminated folded dipole is a good example.  There's no real way for it to have a better signal to noise ratio than a regular dipole in terms of RF pickup.

But there's a good reason why people think they're "quiet" and why they like them.  

Here's a sound file where I switch between my "quiet antenna" and my "noisy antenna" while listening to some guys on 75m.  


I think it's pretty obvious when I switch.  I start with the "quiet antenna" and switch every 10 seconds.  The guys who are a little down in the noise are really better copy on the "quiet antenna" and the guys well out of the noise are pleasant to listen to, while the "noisy antenna" has very choppy and harsh noise.

There's one very simple difference between the "quiet antenna" and the "noisy antenna"  The "noisy antenna" is a 1/4 wave ground mounted vertical for 80m, 60 feet tall with as many radials as I can fit on my small piece of land.  The "quiet antenna" is THE EXACT SAME ANTENNA with my attenuator switched on on my radio.  Zero difference besides knocking the signal down 20dB.

My little FT-857D just can't gracefully handle the giant amplitude broadband QRN signal with loud hams on top presented by a highly efficient antenna on the 75m band.    But the difference between my "quiet antenna" and my "loud antenna" in this test is that I intentionally added all that loss using my radio, and as soon as I press the PTT on my microphone, the loss gets switched out.  You can't do that with a terminated folded dipole!  If I need more attenuation I can also turn the RF gain down.  I actually had to do that ALSO with my vertical to make the "quiet" situation sound good.

The antennas that W0BTU mentions are different.  They are antennas that give a directional pattern.  They also happen to be lossy, which as you can hear above isn't a very big deal on 75m, and actually can be HELPFUL as you can hear above.  They are really better than a dipole antenna in terms of real signal to noise ratio because they sort of "focus your ears" in a certain direction.  And that's all that matters.  If anyone tells you they have a special type of  dipole type antenna that's quieter than another dipole, you should be very skeptical.  Same goes for loops, which are widely held to be quiet... except for some special cases involving static discharge noise, they just can't really be better than a dipole.    But things like Beverages and K9AY loops have different pattern than a dipole, so they really are different.  

I gotta tell you though, I use a flag which is an awful lot like a K9AY and the difference is VERY subtle. Much more subtle under most conditions than my attenuator tests.  I have to be very careful to attenuate the transmit antenna down to the same level as the flag and listen very critically to hear the difference.  There is a real, audible  difference, but it is not something that will simply and obvioiusly pop signals right out of the noise compared to my vertical transmitting antenna.  The only time it's really obvious is when the noise is concentrated so that I can put the rear null of the flag right on the noise.  Then the difference is profound.  A big Beverage has a tighter pattern so will give a much more obvious improvement than a K9AY or flag.  

But I wouldn't go for "low noise" antennas until you figure out why the regular ones are objectionably noisy.  

- - - - - -

In addition to people making stuff up about "quiet" vs. "noisy" antennas of the same basic radiation pattern, there's the issue that there is absolutely no such thing as an antenna that can preferentially reject "man-made noise" and leave the natural background noise and signals intact.

You can certainly get improvement on a case by case basis.  A noisy streetlight atop an aluminum pole with buried power lines is very likely radiating vertically polarized radiation.  So a horizontally polarized antenna will do better because it's cross polarized to that noise source.  But beware of people who tell you "verticals pick up less man-made noise."  In some cases on some bands at my location for power line/streetlight type noise I find EXACTLY THE OPPOSITE of that, probably due to the fact that I've got a lot of relatively nearby above-ground power lines.  In some cases my verticals are noisier and in other cases it's the horizontals.  I've had situations in which I can switch polarization and hear one noise on one antenna and a different noise on another.

There is no antenna that is generally more immune to any kind of radiated noise.  That's a physical impossibility.  

Sometimes, though, noise is not radiated, per se.  If your feedline is poorly decoupled from your antenna ... like you have a bad balun or no balun and a bad length of line... the outside of your coax can act as a very direct path from your noisy house to your antenna.  In these cases, a choke at the antenna feedpoint can be very helpful, as can be finding the source of your noise.  And choking can help even if you don't think you have feedline current.  You might not notice a current of 1% of the antenna current on your feedline as "RF in the shack" when you're transmitting, but a noisy device exciting a tiny bit of current on your feedline and coupling 1% of that tiny current to your antenna could still give you lots of noise.  

Many people don't control for this when they develop their opinions about "quiet" vs. "noisy" antennas.  They just pick the one that "hears better" and they call it the winner, when it's possible that at another ham's shack, exactly the opposite would be true.

 So be careful with advice, and seek out information about how to get rid of noise on antennas in general, not about what type of antenna is "quiet."  Many people are just making stuff up when they insist their antenna is "quiet."  They have their hearts in the right place and they're not lying to you.  A lot of people just have the wrong explanation in mind for why it's happening, and so their results won't translate at all to your house.  Unless, of course, your good antenna is overloading your radio and you replace it with a bad antenna instead of turning your attenuator on and your RF gain down ;-)


" I thought that a beverage antenna was only good for recieve?

Yep... it's hard to build efficient directional antennas on the low bands.  They have to be huge. But if you give up efficiency, you can make very directional antennas that let you listen directionally.  Then you transmit on a single vertical.  

The efficient transmitting 75m/80m equivalent of a Beverage in terms of receiving pattern is something like circle of 8 1/4 wave verticals about 200 feet in diameter ;-)

The efficient transmitting version of something like a flag or K9AY is a pair of 1/4 wave verticals spaced 1/4 wave apart.  

But I wouldn't worry too much about receiving antennas.  If you put up an efficient transmitting antenna of any kind and work on fixing its noise issues as you find them, you'll do fine.  Special receiving antennas are NOT noise immune either.  In fact, some of the smaller ones can have equal or worse issues with noise conducted from your house.

We live in a noisy world these days, and you can work up an overall station plan to help that: antennas, quiet house electronics, using your radio to best advantage, etc.  But the "quiet antenna" is a myth that at best is being told to you by a good natured ham who caught a lucky break, and at worst is coming from some huckster who wants to sell you something .



[0] Message Index

[#] Next page