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Pictures of my current antennas

• Cushcraft 11-Element Yagi
  • PDF of Manual
  • PDF of Insert

Here are some of the antennas I have built.

• St. Louis Vertical (10-40)
• Coax Trap Dipole
• 2-Meter Colinear (FM)
• K0FF Square Copper Dipole
  Here are some additional notes on the K0FF square loop
  
  • I did a quick field-strength test using a rotating jig I made from some old work parts. Click here to see a plot of my results. (These results should be verified independently.) The direction of the strongest lobe is in the direction 180^o from the gap.
  • Using Nibco copper fittings the I cut the 1/2" copper pipe to the following lengths:
    • 2 x 10-3/16"
    • 2 x 4-13/16"
    • 2 x 3-3/8"
  • 3/8" copper tube length is 4-3/4"
  • Brass plate dimensions: 1-1/4" x 2-1/4"
  • RG-8 insides length is 6"
  • For the gamma section, I used two pieces of Oatey 3/4" copper tube strap. When flattened these are 1/2" x 3-3/8". For the 1/2" pipe section, make a 90 bend at 5/8" from the end and then wrap around the copper pipe. This will make the small holes in the strap line up. Then do the same thing with the other piece and the 3/8" tube but make the bend at 15/16". You can then put the pieces on the antenna and use a single bolt through the 4 holes and it will all work great. I usually drill another hole close to the 3/8" tube and add a 2nd bolt.
• KB1DIG 2-Meter Halo
  Here are some additional notes on the 2-Meter Halo
  
  • First of all, here is a link to KB1DIGs 2m Halo Page
  • Closeup of single halo feedpoint
  • You can use a piece of vinyl tubing to join the two ends of the circle but if you plan on doing this, make sure you put it on before you start trimming and tuning. It will affect the tuning of the antenna.
  • You can stack a pair of these antennas for higher gain. It is still omni-directional but if done right it will give you almost the same gain as a 3-element beam. Here are some more notes on stacking.
    • Don't cut your 1/2" pipe to 20"...make it 24". This way, when you build 2 and put them end to end with a coupler they will be space 48" apart.
    • Build the 2nd halo with the gamma match on the other side. This way when you flip one over the gamma matches end up on the same side which is important for phasing.
    • Feeding a stacked set isn't quite as easy as feeding a single halo. In order to work properly they have to be in phase. The simplest approach I have found is to use a SO-239 Tee. The 50 ohm feedline goes into the tee. You then need to have one odd 1/4-wave section of 75 ohm feedline coming out of the tee to each loop. Getting the proper length can be a bit tricky. First of all, do to the design of the gamma match I'm not exactly sure where the 50 ohm feedpoint is. I assumed it was at the base of the 1/2" pipe so after calculating my 1/4-wave length, I added 5" for the section with the shield removed. You also need to take into account the velocity factor of the 75 ohm coax. The standard equation for a 1/4-wave section is:
         1/4-wave(ft) = [245.9/f(MHz)] x VF
      I'm designing around the calling frequency at 144.2 MHz and the velocity factor of my coax was 0.81. Therefore, a 1/4-wave section comes out to:
          (245.9/144.2)x0.81 = 1.381 ft or 16-9/16"
      I used a 1/4-wave section for the lower halo and a 3/4-wave section for the upper halo. Don't forget to add the 5".
      Here are some interesting links:
      • W6OAL Article on Power Dividers
      • W3RJW on Waveguide Power Dividers
      • Disussion on stacking squalos (square halos)
      • Building a 4-Way Power Divider
      • Rochester VHF Group Journal Oct 2004 - See page 6 for K2AXX Power Divider