1、as a further part of this research i took another look at the reviews for the cha-250 on eham, as i couldn't understand why some folks got good results with the antenna and others seemed to have really bad ones.
2、from the replies i received and further analysis of reviews i concluded the following:-
the main problem would seem to be the suggestion that the antenna will work with no radials, ground plane or counterpoise wires. this means that if none of these are installed, the antenna will use the coax cable as part of the radiating structure. this can result in very unpredictable results. i would strongly suggest that some form of ground plane is used. either ground mount the antenna and connect at least 4 radial wires to the outer screen of the coax at the base of the antenna, or if the antenna is mounted on a pole, add a minimum of three sloping radials (at least 5m long) as this can dramatically improve the performance.
3、many people had unrealistic expectations of antenna performance, especially on 3.6mhz where comparisons were made with dipoles, frequently for medium distance contacts. the antenna is electrically short on 3.6mhz so even if an auto-tuner is used the performance will still be 3-4db down on a 1/4 wave vertical (20m high). the loss in the matching transformer at this frequency reduces the gain by a further 13db, so the total gain at 3.6 mhz is about 17db less than a 1/4 wave vertical.
4、here are some gain measurements i made of the cha250 (1) and my version (2) feeding a 7m vertical and compared against a 1/4 wave vertical.
附图：cha-250a与g8jnj自制的改进型巴伦和7米长垂直天线的增益对比图。可以看出除了10-24兆外，该天线增益和效率太低，基本没有什么使用价值。可况一些人还根本没有使用人工地网。
有兴趣的爱好者可以看看g8jnj :
http://g8jnj.webs.com/cometcha250b.htm
