Paul, my call sign just showed up tonight on the FCC database. Yahoo!
I'm considering a vx-7r and looking at improvements to the stock antenna. Your Yagi is intriguing and a brilliant design, and just has to be better than a tiger tail. I think this will be my first homebrew project in Ham radio. My question is, do you figure out the tuning at home and then call it good, marking the feed points, or do you tune it in the field? If you tune it in the field, how?
Hey, congratulations and welcome to the hobby! Post your callsign in your signature.
If you build my yagi exactly as described, it should be tuned and ready to go. Won't make that much difference at 5 watts. It doesn't use a matching network, so a VSWR swing of 2:1 is no big deal. I modeled it to be hi-gain but very forgiving. I think mine bottoms at 1.3 and tops at 2.4 across the band. The gain more than makes up for any impedance mismatch. Make sure you use 174U as feedline and order some SMA connectors from Mouser or Digikey for 174U. The copper sub-mini alligator clips are what works best at the feed point.
Note: You can use a wooden arrow shaft as the boom if you want, but the carbon shaft allows for element storage when you pack it. Have fun!
Hint: Once built, IF you can talk your park rangers out of the radio collar frequencies of bears/cats, you'll be able to pin point their locations. <img src="/forums/images/graemlins/cool.gif" alt="" />
Thank you both! My HT arrives on Wed. I just found an open repeater at a pass in the Cascades that links to a repeater in my hometown. It is a location that I frequent often for backcountry rambles. Now, if I could just get my wife and son licensed.... Otherwise, I'll have to cajole the local club members to monitor while I'm out.
Thanks again Paul. I just finished it today. I am astounded at how well this antenna goes together and how light it is. I used .047" music wire so less droop or wind effect and moved the driven element about 1" closer to the director. This gave (theoretically) close to 50 ohm input impedance and almost null reactance with a loss of 0.3 dBi gain compared to your parameters. Six of one, half dozen the other. I'm bottoming out at 1.10 VSWR at 146 MHz with 1.21 and 1.41 VSWR at the ends of the band. This was measured with a Bird 43 with a 250 mW element on the reflected power, so it is accurate.
Your design is ingenious. I'm going to have good times with this.
Hey great! Glad you like it. Moving that element probably doesn't change the pattern much. I can model it to see but really, as you say, it won't matter. Now, go enter a few local 'transmitter hunts'! You'll find the antenna is very effective running through the trees and not breaking. You'll find you can hit repeaters impossibly far away as well as satellites, with ease. Enjoy!
MNS, you must understand (and take pity... <img src="/forums/images/graemlins/grin.gif" alt="" />)...huskyrunner and I are geeks and have "the knack". <img src="/forums/images/graemlins/cool.gif" alt="" /> It's a disease acquired at birth.