Today and after many years of operating with an end fed antenna, I have learned that these antennas give off lots and lots of unwanted radiation, also known as common mode currents. So what's the answer? New antenna? More coax, less coax? Read on and I'll hopefully answer these questions!
Common Mode Currents
Otherwise known as: An end fed wire antenna is considered an "unbalanced" antenna.
Any modern transceiver has an RF output of 50 ohms, unbalanced. We get the terms balun and unun from the combination of two words - balanced-unbalanced and unbalanced-unbalanced, respectively. A random wire uses an unbalanced transformer because we are feeding the output of our radio directly into the antenna, hence it's an end-fed antenna, which is fed at one end. Since our impedance here is no longer 50 ohms but more along the lines several hundred ohms, we use a 9:1 ratio unun to transform the high impedance into one that is much more manageable for the radio or tuner.
Here's where the problem lies. An unbalanced antenna can have RF running along its feedline, since the feedline can act as a counterpoise. These antennas are designed like this on purpose. This creates an RF field on the coax which can introduce RFI, EMI, and all sorts of other menacing problems into the shack, your house, and even other electronics inside your home! I remember when I first got my FT-891 and connected the random wire to it, I noticed that my LED light would sporadically change color temperature or shut completely off every time I tried tuning up on 80 meters! Was it the ghosts of Yaesus past? Nope - just some pesky RFI.
Despite having my antenna lofted up outside, a ground/lightning arrestor along the coax line, and a grounded electrical outlet from which I run my equipment, I am still getting severe RFI which still trips the GFCIs around the house and now even shuts down my computer or sends random characters from the keyboard! It's so terrible what RFI can do, but it all boils down to one thing - common mode currents.
So why don't we see this problem with antennas like inverted Vs, delta loops, or even basic dipoles?
Bringing Balance to the Waves
That is where a balun comes into play. A balun is similar to an unun, except that it TRANSFORMS an UNBALANCED signal into a BALANCED signal - hence, balun. Baluns come in all sorts of shapes and sized. The most common include 1:1 and 4:1, but even 2:1 isn't unheard of.
A balun will take the unbalanced signal from our 50 ohm output and feed it into the balanced input of our antenna. An antenna is considered balanced when the impedance is purely resistive, or the capacitance and inductance of said antenna cancel each other out. A dipole is a prime example of a balanced antenna.
Most dipoles are fed with 1:1 baluns since it just makes sense. You COULD feed your unbalanced output directly into the dipole (as is the case with my previous project, the speaker wire dipole) but this would most certainly introduce common mode currents as horrible as an end fed would. A balun will help attenuate and in most cases eradicate common mode currents. Since dipoles have a relative impedance at the feed point of a little over 50 ohms, we can use a 1:1 balun to transform our 50 ohms unbalanced to 50 ohms balanced. The balun ensures that any stray current is kept to a minimum.
Now antennas like delta loops and even G5RVs are matched with 4:1 baluns. These antennas, like dipoles, must be fed with a balun. Again, we are feeding our unbalanced 50 ohm output to a balanced impedance.
What about End Feds? How can I stop CMC?
End feds still work, but they are unbalanced. To be balanced, an antenna needs to distribute the signal evenly across two conductors. End feds will always be unbalanced since we are only feeding one conductor, and since there is no counterpoise radiator (usually), our coaxial shield acts rudimentarily as the other leg. This is where common mode currents are introduced, end of story.
So again, we'd need to feed our unbalanced 50 ohms from our radio into the unbalanced antenna. Random wires are almost always fed with 9:1 ununs, whereas EFHWs are fed with either 49:1 or 64:1 ununs.
There's no by-laws or rules in ham radio that says you can't experiment. In fact, that's what this hobby is all about - experiment!
There are many ways that you can tame that hellacious end fed to be RFI free, and the easiest way? Add a balun.
No, seriously, add a balun! A 1:1 balun or choke can ensure that your antenna is free from almost every little bit of RFI emission. There are many ways to do this such as adding a balun at the input of the unun or clamping on ferrite beads to your coax at the antenna's feed point. If you are doing this, make sure to stick with a good mix. FT-240-31 toroids have the best chance of suppressing common mode currents, and in fact a few wraps of coax around such a toroid can act as a balun.
How else can I solve common mode currents, RF noise, etc?
After constructing my station, I have come to the following conclusions:
- Ground your antenna - your antenna not only needs to be protected against lightning and static buildups, but it must have an excellent path to ground. Purchase a lightning arrestor and add a ground stake just below the arrestor. Bond both the ground rod and arrestor together with bare copper wire, and you're done! Ground secured
- Ground your equipment - Grounding your equipment prevents unwanted RFI and other interference from entering your devices. Make sure to use a ground strap to ground at least your radio and tuner. Also ensure that the plug you are plugging your items into is grounded. An ungrounded outlet is not only dangerous but is also important for your station.
- Use ferrite beads as often as you can - put them on your coax, your power lines, your audio lines...everywhere! Even the cheap ones off of Amazon seem to work excellent and well for what they need to do, but if you must be specific, look for Mix 31 snap-on beads.
- Add an RF reference plane - while it may not be necessary, I feel that it's a good thing to add here. Find some metal roof flashing (aluminum or copper) and place it like a placemat under your electronics and your radio. You'll more than likely find that this will improve your radio and station's performance. An RF reference plane helps repel RF and keep it out of your devices, but just know that this alone isn't enough to stop RFI.
The Plan Now
Sadly, I have no other choice but to closet my 9:1 unun. For portable operations, I will use it. But for a more permanent solution, I'll have to use my Chameleon antenna I purchased with my FT-891. I am once again on a tight budget and I'm afraid I can't really swing any more purchases as of right now. Luckily, I have a purchase that I made a year or two ago that might just save me.
The Chameleon CHA TD LITE is a tactical dipole antenna that is more suited towards portable ops, but will work great as a base station antenna. It is useable on all bands from 160m to 6m, making it the best and perfect partner for my 891 and the LDG tuner I use. The best part about this antenna?
It has a balun.
Yes, a balun! I'm crossing my fingers that this will help solve my crisis of having RFI bounce every which way in the shack and will stop me from blowing the GFCI outlets every time I key up. I also hope that it will help prevent my computer from shutting down every time I'm on 80 meters or so. Plus it's durable, dependable, and absolutely built like a tank. After all, Chameleon antennas are used by our heroes in camo!
As far as I know, the transformer used on this setup is rated as a 1:1 balun. Like the CHA TD 2.0 that's being produced now, it comes with 2 lengths of 60 foot Kevlar-coated wire. In addition, it comes with wire winders for the antenna which will make it much more easier to stow and store away when I'm done operating for the day or night - it should take at most 15 minutes to set up and tear down too! I will be putting this antenna in an inverted V configuration where the balun will be hoisted at least 20ish feet in a tree and do plan to use it on all of the HF bands, 80 through 10. 160 if I'm lucky :)
I originally purchased the antenna for $165 new from Ham Radio Outlet. I have used it a few times and have gotten excellent signal reports, even when it was arranged in the most compromising positions. If you're looking for an antenna producer who makes quality and durable antennas, Chameleon has to be my pick by far. I'm a fan of simple wire antennas and these folks sure do deliver!
Conclusion
I could spend all day telling you about how baluns and ununs work. However, I am nowhere near as studied up as Dave, KE0OG, over on YouTube. Over the past few days I have been watching his videos on baluns where he debunks the argument if they are necessary or not. Dave also does a good job explaining how baluns interact with antennas, both technically and in layman's terms. Go give Dave's channel a visit!
For your reading pleasure, make sure to also check out a PDF article by G3TXQ explaining all the different kinds of baluns. You can find that here: http://www.karinya.net/g3txq/baluns/baluns.pdf.
So after all I've discussed, is a balun worth it?
Yes, 100% it's worth it! If you suffer from common mode currents, RFI, or any other electrical phenomena, look into creating or purchasing a 1:1 balun for your shack. Better yet, consider upgrading your antenna if you have the real estate and property to do so. Antennas aren't always a one size fits all fix, so don't be afraid to try new things!
The end fed random wire antenna will ALWAYS be my favorite antenna, don't get me wrong. These antennas can be used in confined spaces, placed in compromising positions, and yet they still by some miracle deliver actual results. After making my first 10W SSB contact to Italy using this antenna, I can say with full confidence that this antenna will forever be a part of my ham radio arsenal. I've tested it on all bands from 80 to 10 meters and have gotten SWR readings near 2:1 at most! Yes, at most 2:1.
However, I think it is time to retire this antenna in favor of equipment and electrical protection. While I can't guarantee 100% that this problem will be fixed, I am hoping that using an antenna with a balanced component will, in essence, remove and reduce the common mode currents that are wreaking havoc on my equipment and my house's electrical system.
I'll be back with an update once I get this antenna installed. Hope to hear you on the airwaves soon! Stay radioactive and 73s!
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