January 17, 2012

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What's the BEST Antenna? 

A popular discussion topic wherever hams gather is “What is the best antenna?” Obviously no antenna is best for all situations ... Like most things in life, choosing an antenna is a process of balancing exactly what performance you need against size, weight, the antenna environment and the always-present issue of cost.

In this week's session we discussed what we've found to be useful in many of our operating settings over the years.  Take a peek at the discussion notes and configurations below ... perhaps you'll recognize a few of these antennas!

73,
~George N2APB & Joe N2CX

Audio Recording ... (Listen to MP3 recording)

Text Log from this week's session ...
<20:12:10>"George - N2APB": "A single-band dipole with coaxial feed is the basic choice. By dispensing with a balun (of course you can use one) you minimize weight and complexity. For my portable dipoles I use 20-22 ga stranded hookup wire and RG-174 to make an inverted vee antenna for any HF band from 40 thru 10 meters that weighs less than a pound and fits in a zippered food storage bag. No tuner is needed. I simply raise it in the air, hook up a rig and get on the air."
<20:16:08>"George - N2APB": 1/4-wave length of wire is a low impedance
<20:16:21>"George - N2APB": And thus us a good match to a 50-ohm coax
<20:16:53>"George - N2APB": 1/2-wavelength is a HIGH impedance
<20:17:35>"George - N2APB": But convenient to feed from the end point ... sloper up, out ... and use a tuner with high-Z output
<20:18:00>"George - N2APB": Important to match the output of the transmitter to the right impedance of the antenna
<20:19:02>"George - N2APB": Fan dipole (multiple legs of different lengths) only has one set of wires resonant at a given time ... the others are high-Z and thus do not affect primary operation on the resonant legs
<20:19:45>"George - N2APB": 40m dipole can also be used on 15m ... 3x the length also works
<20:21:01>"George - N2APB": Ground (or counterpoise) is not needed for a dipole
<20:21:50>"George - N2APB": However a counterpoise (ground) is indeed necessary for an End-Fed Half-Wave antenna (EFHWA) to handle the current in the other half of the antenna
<20:22:32>"George - N2APB": End Fed Half Wave Antenna - AA5TB http://aa5tb.com/efha.html
                                AD5X Portable Vertical Antenna www.ad5x.com/images/Articles/VerticalRevH.pdf
                                Homebrew PAC-12 Vertical Antenna  http://www.njqrp.org/pac-12/
<20:23:27>"Bruce - N1RX": sometimes, when feeding an end fed half wave EFHW antenna, just the length of the lead to a morse key and your headphone lead can serve as an adequate counterpoise 8-)
<20:23:34>"George - N2APB": A tuned counterpoise can help make the antenna more directional
<20:28:22>"George - N2APB": MFJ "ground tuning box" ... address anyone?
<20:29:04>"Frank N3PUU": this one perhaps? http://www.mfjenterprises.com/Product.php?productid=MFJ-931
<20:29:57>"Joe - N2CX": That's the one Frank!  Thanks for the link.
<20:32:17>"George - N2APB": Baluns
<20:33:02>"George - N2APB": Ladder lines -- efficient, balanced feedline ... useful when using a single wire on different bands
<20:33:44>"George - N2APB": These present typically present much lower losses, especially when there is an unbalanced match at the antenna
<20:33:48>"Joe - N2CX": Balun stands for balanced to unbalanced transformer to adapt between a balanced and unbalanced situation.
<20:34:36>"George - N2APB": All-band doublet fed with ladder line
<20:34:49>"George - N2APB": can be seen at http://www.hamuniverse.com/hfdoublet.html
<20:35:37>"Frank N3PUU": I run a 44' doublet here, fed with tv twinlead.
<20:36:07>"Bruce - N1RX": I use the 88 ft w/tv twinlead when camping.
<20:44:50>"George - N2APB": Feedline bibliography (collection of useful links) ... http://www.dxzone.com/catalog/Antennas/Feed_Lines/
<20:45:27>"George - N2APB": 4-wire transmission (feeder) lines??
<20:45:53>"George - N2APB": Use of twisted pair as a feedline?
<20:46:04>"Pete - WB2QLL": They use four wire on old commercial short wave facilities
<20:46:48>"Pete - WB2QLL": That was the idea, better balance and lower loss
<20:47:52>"George - N2APB": Do You Need an Antenna Tuner - Maybe yes, maybe no. It all depends on the type of antenna and feed line you're using. QST Article in pdf format ... http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=10118
<20:49:05>"George - N2APB": A T-Match ATU - An homebrew antenna tuner project ... http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12591
<20:49:08>"Larry-W2HHV": See  http://www.rfcafe.com/references/electrical/transmission-lines.htm
<20:49:52>"Larry-W2HHV": See Balanced 4-Wire Array at http://www.rfcafe.com/references/electrical/transmission-lines.htm
<20:57:26>"George - N2APB": Images for folded dipole antenna ... http://www.google.com/search?q=folded+dipole+antenna&hl=en&biw=1350&bih=947&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=6iYWT7CRH8fTgQeqhfXWAw&ved=0CGwQsAQ
<20:58:51>"George - N2APB": Folded dipole presents a broadbanded (wider) bandwidth by quadrupling the characteristic impedance of the 75 ohm antenna
<21:01:16>"George - N2APB": OCF = Off-Center Fed Antenna ... http://www.w8ji.com/windom_off_center_fed.htm
<21:01:39>"George - N2APB": "The modern common Windom antenna is not an original single-wire fed Windom, but rather an off-center-fed or "OCF" two wire feed dipole. The normal Windom is described as having a 1/3 length leg, and a 2/3 length leg. In other words an 80-meter Windom 137 feet long would have one leg 45.667 feet long, and the other leg 91.333 feet long."
<21:01:58>"George - N2APB": "Windom's original idea was off-center feeding a horizontal antenna to present a feedpoint impedance of 600 ohms. This is close to the surge impedance of a single-wire feedline, allowing an inexpensive single conductor to be used as a feedline. "
<21:02:30>"Ray K2ULR": The Buddipole is an off-center fed antenna.
<21:02:40>"George - N2APB": Survey of Published Multiband Windom Designs (80m and up) ... http://www.qsl.net/on4baa/mirror/antennas/windom.html#survey
<21:03:31>"George - N2APB": Images for carolina windom ... http://www.google.com/search?q=carolina+windom&hl=en&biw=1350&bih=947&prmd=imvnso&tbm=isch&tbo=u&source=univ&sa=X&ei=WCgWT_vgKIn4ggfSqYj1BQ&sqi=2&ved=0CEEQsAQ
<21:03:34>"Ray K2ULR": But..... off center fed.. by adjusting lengths of the dipole.
<21:04:20>"Bruce - N1RX": A popular OCF antenna is the Fritzel FD-4: http://www.radiowave.ro/lang-en/dipole/248-fritzel-fd4-ama-1641.html
<21:04:34>"Joe - N2CX": OK but what is the advantage of an OCF Buddipole?
<21:06:03>"Ray K2ULR": The BP is low to the earth for many bands.. only 8 feet sometimes.
<21:06:06>"George - N2APB": EVERYTHING radiates!  Actually, we try to control radiation such that it goes up to the antenna and not from the feedline, or even from the "finals" of our transmitters.
<21:07:29>"John-KJ6CVB": Why not put transmitter high up at feed point (no feed line) and send audio freq to shack?
<21:07:56>"Joe - N2CX": Bonding chassis and cables together can minimize unwanted noise radiated from your digital stuff.
<21:08:02>"George - N2APB": Great question.  There are some reference designs for this.  Perhaps Joe can address this one.
<21:08:18>"Ray K2ULR": So he feed impedance is very low.  The elements are coil loaded, but you have to reduce the length of one of the telescoping whips.. -so that- the feed impedance will be close to 50 ohms.. and not 12 ohms, for example.
<21:09:11>"Joe - N2CX": OK, I can see that - did not think that anyone went to that degree of effort.  Thanks for the info.  Joe E.
<21:10:41>"Joe - N2CX": This is a good time for GFI buzz to rear its ugly head on someone's headset.
<21:11:15>"Bruce - N1RX": RFI Tutorial- a must have! by Jim Brown, K9YC: http://audiosystemsgroup.com/RFI-Ham.pdf
<21:16:45>"Bruce - N1RX": Also a wealth of info available from Charles, W8JI, here: http://www.w8ji.com/
<21:20:08>"Joe - N2CX": You obviously did not have GFI outlets back then!
<21:23:46>"Frank N3PUU": I believe Motorola published a book on grounding, although it may have been geared primarily at lightning protection
<21:24:12>"Bruce - N1RX": Station grounding matters: http://www.w8ji.com/ground_systems.htm
<21:25:21>"John-KJ6CVB": Sources/part numbers for mag loop butterfly var caps?
<21:25:33>"George - N2APB": Magnetic Loop Antennas - AA5TB http://www.aa5tb.com/loop.html
<21:25:42>"George - N2APB": Magnetic Loop Antennas - W2BRI  http://www.standpipe.com/w2bri/faq.htm
<21:25:53>"George - N2APB": Midnight Loop  http://midnightdesignsolutions.com/     Click on Midnight Loop for 4.5MB PDF
<21:26:41>"George - N2APB": How to build ... http://www.google.com/url?sa=t&rct=j&q=mag%20loop%20butterfly%20var%20caps&source=web&cd=1&sqi=2&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.standpipe.com%2Fw2bri%2Fsource.htm&ei=yi0WT9m4NsvdgQfYgpDGAw&usg=AFQjCNG2-f2Dt2ceCbAMZtO40mbrBzqbTA
<21:27:24>"Frank N3PUU": Here it is, Motorola R56 Manual... it is encyclopedia sized but has excellent information regarding grounding: http://www.radioandtrunking.com/downloads/motorola/R56_2005_manual.pdf
<21:31:28>"Bruce - N1RX": HATE plasma TVs!
<21:35:44>"Pete - WB2QLL": Someone should do some work on dielectric loaded antennas for ham use.

Session Notes ...

 

A single-band dipole with coaxial feed is the basic choice. By dispensing with a balun (of course you can use one) you minimize weight and complexity. For my portable dipoles I use 20-22 ga stranded hookup wire and RG-174 to make an inverted vee antenna for any HF band from 40 thru 10 meters that weighs less than a pound and fits in a zippered food storage bag. No tuner is needed. I simply raise it in the air, hook up a rig and get on the air.

 

 

 

 

 

 For portabling, the inverted vee is often the best way to hang your dipole. It needs only one high support and the center support line allows using small-gauge wire for the dipole elements. The ends should be as high as possible but can usually be tied off to easy-to-find supports like shrubs, fences, picnic tables or cooperative on-lookers.

Of course you want your antenna as high and in the clear as you can get it but there are a couple of rules of thumb to help you decide how high to shoot for. Try to get the center up at least 15 to 20 feet or you will do no more than warm up earthworms. If you are operating on 80 or 40 meters most of your contacts will be fairly close in so you may want to optimize things for NVIS (Near Vertical Incidence Skywave) operation.  Low horizontal dipoles or inverted vees are best. Anything less than a quarter wave (33 feet on 40 or 66 feet on 80) is low. On the higher bands you should aim to get your antenna up at least a quarter to a half wavelength or more up to emphasize low angle radiation. If your antenna is higher than these guidelines it will work for either local or dx operation.

 

 

 

 

Another way to get low angle radiation is by putting the dipole up as a sloper. It is somewhat directional toward the downward sloping end. And if you have a really high support, you can always put up your dipole vertically. This ensures a low angle of radiation.  Just remember to bring the feedline away from the dipole elements at least a quarter wave.

So there you have it!  In my opinion, if you want good repeatable portable antenna performance use a dipole!

 

 

 

 

Want a multi-bander? That’s simple! The “fan” dipole uses quarter-wave elements for several bands fed by a common feedline for “no-switch” operation on multiple bands. A dipole segmented for several bands with insulators is sometimes called a “Leap Frog” antenna. To change bands, the appropriate insulators are jumpered with short alligator clip leads.

 

 

 

 

If you can take along a small tuner (such as the excellent Emtech ZM-2 or the clever NorCal BLT) and carry a little more weight, a very good multiband antenna replaces the coax cable feedline with open wire line or 300 ohm “window” feedline.  Such a dipole with 33 foot (or longer) legs operates effectively from 80 through 10 meters.