Many new to VHF SSB are trying to use their verticals that they use on FM and wonder why they can’t hear very many people on the local nets or in general. The biggest reason is that antennas used for VHF SSB operations are predominantly horizontally polarized. Now this doesn’t mean that the newcomer to VHF SSB has to go out and spend a lot of money for some 10 or 20 element two meter antenna to be able to participate in the local VHF SSB activities. A very simple homebrewed four element yagi (48” boom) on a 20 or 30 foot pushup mast will allow you to hear a greater number of the participants on the local nets, depending on your location. A horizontally polarized yagi will also allow you to hold QSO’s with hams all over the state and other states should we get a good E-skip opening. I have 36 states confirmed on two meters myself using SSB and CW. Much of it was being at the right place at the right time
I wrote a piece on antennas a while back called “Woodies.” It seemed at the time to garner some attention but I think maybe its time to take a look at the very simple yagi type antenna again. The basic material for a very simple yagi antenna for the two meter band can be aluminum clothes line wire for the elements and a straight wooden tomato stake that can be found in the garden department of the local hardware emporiums. I don’t think we can get much simpler than that.
The dimensions of elements and spacing of those elements can be found in most any Amateur Radio Handbook, VHF Manual, etc. To save you the trouble of even finding yagi building references, I’ll supply them here and now. The reflector of a yagi will need to be on the order of a half wavelength. A yagi on the two meter band will then have a reflector length of one meter (39.37 inches) or to be a little more exact use the constant 5600 and divide it by the frequency of interest in MHz. Most SSB operation on the two meter band takes place around 144.200 MHz. Therefore, 5600/144.2 = 38.8350. I’d make it an even 39”. If you are using clothesline wire, roll off 39” of the stuff, cut it to length and straighten it as best you can by hand. It can be made real straight using a hammer and a small anvil as on the back side of a bench vise. Lay the reflector aside and next make the driven element which will be about 3% shorter than the reflector, 39” – 3% = 37.83”. I’d make it 38” long. Again cut a 38” length from your roll of clothesline wire and straighten it out as best you can. It doesn’t have to be absolutely straight as the electrons traveling down it won’t know the difference. Lay the driven element aside and let’s make the first director element. The first and second directors will be 3% shorter than the driven element, 38” – 3% = 36.86”. I’d make them 37” long. As before cut two 37” lengths from the roll of clothes line wire, straighten them out and put them aside.
We now have to prepare a boom on which to mount these elements. The wooden tomato stake that you found at the hardware store measuring about ¾” X ¾” square you will want to be on the order of 4 feet long. We will want the reflector to be spaced from the driven element about 0.2 wavelength. A free space wavelength at 144.2 MHz is about 82”, so 82” X 0.2 = 16.38”. I’d make it 16.5”. A couple of inches in from the end of the wooden boom drill a hole that will be just a little bit smaller than the diameter of the clothesline wire. Measure 16.5” from that hole toward the center of the boom and drill another hole the same size as the first. Since we are making a simple yagi and not some DX grabbing device let’s just make the spacing of all the elements 16.5”
Find the center of each element and mark it with a “magic marker”, pencil, pen something to give you a reference mark as to the location of the center of the element. Start the reflector element into the first hole drilled. You might have to encourage it with a few blows of a hammer and then push the element all the way to the point where you thing the center of the element will be at the center of the boom width. Follow suite with the driven element and the first and second directors.
Find the center of the boom and drill ¼” holes to accommodate a “U” bolt that will be used to attach the yagi to the push up mast. On what will be the under side of the boom and very close to the driven element drill a pilot hole and try to nick the driven element in passing. Insert a wood screw in that hole and check with an ohmmeter that the screw has contacted the driven element. This is going to be the ground point of the transmission line. You can go ahead and attach a length of transmission line (coax), RG-8, RG-8X, RG-213 – whatever you happen to have available. Keep the length from the radio to the antenna to 100’ or less, the shorter the better. Attach a solder lug to the braid and secure it in place using that wood screw that shorts to the driven element onside the boom. The center conductor of the coax will be attached to a small variable capacitor. A 25 pF mica trimmer cap will work just fine. The other side of the capacitor will be attached to a length of copper wire (#12 or 14) about 10” long. Make a 90° bend in the wire about 7” from the capacitor. Lay the copper wire on the driven element about 1.5” from the bend. Wrap several turns of the copper wire around the driven element and squeeze then tight with a pair of pliers making a good mechanical connection. And that’s about it. Spray some Plasti-Coat or lacquer on the copper wrap to keep water out. The coax can be secured to the boom with a metal strap.
To tune the antenna, an Antenna Analyzer comes in handy but a VSWR bridge will work just as well. With the antenna a few feet off the ground, a point where you can still reach the capacitor, run a few watts of power (say 10) to the antenna and tune the variable cap for lowest VSWR. Use an insulated tuning tool as RF can cause some sever burns. Run a little more power if you have more into the antenna and retune the capacitor for again lowest VSWR. If you can get the reflected power down to nothing showing on the meter great. If you can only get it to where you have 1 watt reflected for 10 watt forward that’s great also as that is below a 2:1 VSWR (10 dB return loss) and anything greater than a 10 dB return loss is gravy, as we say in the business.
See you on the Monday 2M net at 8 PM (144.220 MHz).
Dave W6OAL –
Olde Antenna Laboratory 41541 Dublin Drive Parker, CO 80138