Absolutely pattern is of significance, Alan, but unless you have a lot of space, there's not much one can do about the pattern of HF antennas and most wire antennas will be omni directional at heights most Hams can achieve on typical lots.
Even a full-sized 1/2 wave horizontal antenna is essentially omni directional unless it's at least 1/2 wavelength high in the air! So you need a 66 foot run in the correct orientation with a 66 foot high supports to plan a specific pattern with a simple 40 meter dipole. And, even then, it's very, very broad with a maximum front/side ratio of perhaps one S-unit. Put that dipole up at a more typical height of 30 feet and its maximum radiation is absolutely unidirectional and straight up! You can squeeze some significant directivity out of lower, smaller antennas with Yagi Ueda or cubical quad "beam" designs, but it's fairly minimal unless you can get it up near 1/2 wavelength off of the ground. That's why most Hams don't bother with "beams" - Yagis or Quads - except on 14 MHz and above where they can get them up high enough to be effective. Perhaps the biggest pattern issue most Hams working at HF can reasonably tackle is the question of vertical vs. horizontal polarization, and even then the differences aren't all that great unless the horizontal antenna is at least 1/3 to 1/2 wavelength above ground or the vertical is over an excellent ground (e.g. over salt water) that extends for many wavelengths in at least the important directions. The end result is the vertical vs. horizontal question is usually settled based on the space limitations. That's why few horizontal antennas are found in use on 160 and 80 meters compared to the other bands. On the other hand, efficiency drops like a stone as an antenna is made physically small. That's something we can address, at least in a small way, by getting clever about making the antenna as large as possible, minimizing resistive losses in the conductors and minimizing ground losses. Sometimes Hams are confused when they see patterns published for very small antennas such as mobile whips mounted on a car. An azimuth plot will show a significant pattern suggesting the signal is much stronger in certain directions. That's true, but the important issue is that directivity is a measure of inefficiency, not gain. That is, those patterns show the directions where the losses are slightly lower than in other directions, so the signal appears somewhat stronger in those directions! Those are exactly the things we can address: how to make some small improvement in efficiency that improves the signal. Sometimes we can make our small, low antennas less INefficient in the most desirable direction. For example, a mobile at the beach might discover it's easier to work DX across the ocean in that direction than it is to work someone a few hundred miles away across land in another direction. That's because the losses over the salt water are less than over the land, but it's still not a very efficient antenna. Bottom line is that it comes down to tackling issues we can do something about and not fretting over those we can't. We can often do something about efficiency where we often cannot do something about the pattern. Ron AC7AC -----Original Message----- Interesting discussion. I have a question regarding this topic I hope the more learned in the group cans help clarify. Although efficiency is important is determining an antenna selection, is antenna lobe pattern just as important? If the lobe pattern did not allow you to say work DX or to work a particular direction then is efficiency all that important? Should we look at the desired pattern for a particular operating goal then consider the antenna efficiency? Alan KB7MBI Woodinville, WA FISTS: 5702 CC: 1885 ARS: 582 SKCC: 1988 NAQCC: 058 ARCI: 12141 _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
