When analyzing a J design in the 225-400, you are going to see a better match than you would in VHF, because finding a good match gets easier as you get higher in frequency. The bandwidth automatically goes up as well. But typically you are still going to get a width of maybe 15-20 MHz out to 1.5, and after that it just keeps getting worse. For receive purposes, out to 3.0 isn't going to be a significant difference to the ear. But it gets a lot worse than that... Pretty much off the scale eventually. My equipment goes off the scale at about 1:6, and it does that for a significant portion of the band in that design. Does that mean you won't hear anything in the bad part? No not at all. In fact, you will probably hear a boost over unity in the 20-40 MHz portion in the middle... But you will also hear a degradation on the outer portions of that. The only way possibly around that, would be to create a fat design.
As far as home designs go... Yes, it's true that there is a misconception that simply building something to a specific physical dimension, will guarantee resonance and other factors to be where they need to be. It won't. Materials and dimensions can change things radically, and even installation can change things. Which is why professional level transmission systems really need to be installed and tuned on a system by system basis.
I keep hearing they're switching the 380-400 to land systems only, but I still hear SQ tacs and other stuff on those.
Dave
http://www.dpdproductions.com
- Custom Scanner, Aviation, MURS, GMRS, Marine & Ham Antennas -