1/4 wave ground plane antenna
Here is a nice construction article on building a 1/4 wave ground plane.
This article makes it sound like you have to have accuracies of 1/8 inch or better, and you don't on 2m.
Also, the ground planes can be arbitrarily large. They just have to be longer than 1/4 wave length.
To calculate 1/4 wave, do this forumula: (12*234) / FreqInMhz = length-in-inches
or you could use 234 / FreqInMhz = length-in-feet
Build quarter-wave antennas
You can build a multi-band ground plane by soldering multiple lengths of insulated wire into the top pin.
Spread the wires out at 45 degrees for an inch or so and then run them all up and down parallel to each other.
WA5VJB Cheap Yagi
cheap yagi antennas for 2m, 220, 440
See also WA5VJB CheapYagi PDF
for another article on the same antenna.
Based on WA5VJB's design, N3LTV and I worked out a spreadsheet (Excel 2009 or later) to modify the numbers so we could pick a 420-450 center frequency for the antenna.
Download the spreadsheet from here
Tape Measure Yagi
Construct a portable yagi out of PVC and using cut pieces of tape-measure for elements.
Measuring Tape YAGI for 2meters
HF Dipole Antenna
A dipole consists of two 1/4 wave lengths of wire linearly placed (so they line up end to end) and fed from the middle, usually with coax.
A dipole is the simplest and most common of HF antennas. Most hams use antennas which are worse than a dipole for performance, sacrificing single-band performance for multiband versatility.
But dipoles are so easy to build that this should be the first antenna considered for many situations, especially new hams.
A dipole antenna for 40m is about 70 feet long. 234 / FreqInMhz = length-in-feet
For daytime operation, a 40m dipole located about 8' off the ground is ideal and will deliver communications out to 700 miles or so from a 100watt transmitter.
As a general rule, each band's requirements for best antenna placement is different from each other band.
Thus a multi-band antenna could be multiply compromised.
To construct a dipole the easy way and with nomimal performance, obtain a W2AU 1:1 balun
. They cost $40 or so at a ham store.
Sometimes you find them at hamfests for $10 or so at a used table.
The balun will have heavy-duty rings for tying your antenna wire.
In addition there will be a lightweight copper wire on each side of the balun near the rings. The lightweight wire is where the electrical contact must be for your antenna wire.
Loop your antenna wire through the rings and tie it in a knot, and then solder the stripped and tinned end of your antenna wire to the thin copper wire.
See the suppliers list for The Wireman, or QuickSilver Radio, for wire supplies, or check at the hamfest.
NI4L sells complete dipoles for $60
Tadd's comment on antennas
My understanding of antennas is really limited. But.... i've found some rules of thumb to make things easy. With my tongue-in-cheek method of antenna characterizations.. you have 4 types of antennas
- ground planes
- magic antennas that seem to work
- magic antennas that don't work.
#1 and #2 are really nice to play with and are often what we call Low Q. Low Q is like a pickup truck. It'll last for a long time and take abuse but it isn't particularly great as a race car. High Q vehicles make better race cars but are finicky and break for the most trivial reasons. The magic antennas can indeed work but they have interesting characteristics and are sometimes bizarre in their behavior.
If you use EZNIC you can do some interesting experiments and find antennas that seem to work but are nearly impossible to build to the plan you created with EZNIC. I just love it when an antenna design which is 90 feet long has a piece in it which has to be spaced to a millimeter precision and then only with a meter attached to verify that it works the way the designed specified.
One of the bizarre behaviors I'm not fond of is when RF shows up at the location where there is a human. RF is supposed to show up at your friend's antenna, or at the antenna of all the people around the other side of the planet. It's not supposed to show up in your stereo, or in your computer, or in the IF and AF of the other radios on your bench. If putting your hand on the coax changes the way the antenna behaves, MY read is that you have a problem.
BTW, there are antennas which don't use coax at all. Balanced feed line is actually quite amazing stuff. Building a dipole or loop fed with balanced feed line and with a balun right near your shack can actually be quite nice and low Q. More on that in a different post.
I prefer antennas which make sense and don't let RF come back to the shack.
Some people get really good at this antenna stuff. You might be one of those. Some people are good at keeping a race car going.
So... trivial rules of thumb. Look for an antenna where the feed point comes more or less to the middle of the driven element (and has a balanced to unbalanced transformer or something doing that job, or where there is a ground plane which is made of 1/4 wave radials at the longest wavelength you'll be transmitting at. A 2m/70cm/23cm omni antenna will have 20-inch ground radials. If it doesn't... there is magic in there someplace.
BTW... this is not to besmirch people who really do understand this stuff. But... I lead an effort in our local club to try to keep, retain, hold onto, and to get new hams to stay in the hobby. Dumping serious theory at them when they are NOT asking for it, is not necessarily the ideal method of handling a question.