[quote=老干部]gap的titan也很优秀的，就是内部连线有点烦。[/quote]
同感，我关注gap titan dx 8波段天线很长时间了，因为这款天线为中部馈电的垂直d.p天线，其噪音较小、增益，发射仰角都非常适合做dx，网上好评如潮，垂直天线中效率最高的天线之一。
8 band multiband dx antenna
technical specifications :
+ bands: 10, 12, 15, 17, 20, 30, 40 and 100 khz on 80 meters
+ counterpoise: 4 rigid counterpoises 80 inches long each
+ mount: all hardware supplied except the 1.25 inch o.d. steel mast
+ ground area required: none
+ connector: uhf (so239)
+ height: 25 feet-- 7.6m
+ weight: 25 pounds
网上1/4，1/2仿制的天线太多了，还是看看gap titan dx 垂直d.p如何吧，大家一定会心动的。看看谁能研究一下其构造如何，结构原理等，以便大家制作。我只看懂了8个波段中2-4个波段。其中部分用的是同轴电缆缩短的方式。gap不像其他公司一样，保密工作做得很好，没有透露各个波段的工作原理及内部馈电方式，资料难的公开。
gap titan 主要特点：
gap antennas elevate the feed point. advantage of the elevated feed point design:
1.radiation resistance increases as the feed point is elevated. if the proper elevation is selected, the radiation resistance will be 50 ohms - a perfect match to the feedline.
2.elevating the feed point also virtually eliminated the earth loss. the gap antenna has an antenna resistance of 50 ohms and an earth loss of 5 ohms. this efficiency of approximately 90% creates an antenna with very little loss; if we take the above example 90 watts from 100 watts input will be radiated. the hot spot marking the maximum antenna current is now located close to the antenna center section instead of being close to the earth. result: the rf is radiated rather than used to warming the ground.
3.the resulting antenna gain for low take-off angles increases.
gap antennas feature a high efficiency:
4.no earth loss 5.no loss in traps or transformers 6.the entire length of the antenna contributes to rf radiation. trapped antennas contribute only with a part of their mechanical length to radiating on the higher bands.
7.there are no traps in a gap antenna, no coils nor transformer. here are five reasons to avoid traps:##when not installed properly traps may be prone to take on water
##the coil portion of the trap changes its value as of function of temperature shifting the operating frequency of the antenna.
##a trap is a coil capacitor that operates at high voltage; high voltage in a moist environment is prone to arc and self destruction.
##a trap must have a high 'q' to perform efficiently; a high 'q' will result in a narrow band width and restrict the antennas band width.
##finally, as everyone knows, traps are lossey; they steel transmitter power.
8.
gap antennas don't require tuning.
there is absolutely nothing for you to tune.... in fact, as trip after trip to readjust the antenna on the roof or on the mast raises your frustration level and you may loose your "cool"... all gap antennas come completely electronically pretuned from the factory.
9.
gap antennas have a high band width.with only a few exceptions the gap antennas cover all ham bands featuring a swr of <2:1.
10.quiet - please.noise is an unwanted companion of verticals - particularly on the low bands. all gap verticals are"quiet" antennas primarily due to a sleeved feedline and the use of a counterpoise. gap antennas eliminate the deployment of thousands of feet of radial wires "parallel to" the ac power lines which transfer power line noise.
11.gap antennas are easily installed.just screw the nuts and bolt into the pre-drilled holes with the provided tool!
12.gap antennas are built to lastall weather performance should be important to you. simplicity and a minimal parts count are the key elements to reliability. consider the elements of the gap antenna - aluminum tubes and coax. nothing else! compare that to other antennas with a multitude of connections, coils, variable capacitors, transformers, etc. and you'll see that for everyday operation in rain, sun, ice or snow - gap works. gap antennas use double-drawn aluminum tubing. each section telescopes perfectly into the adjacent and is secured with screws. the hardware is stainless steel. the coax used is a special non-contaminating high temperature type to provide added safety for high power operation.
http://www.gapantenna.com/images/titanfig1.gif
