真正介绍yp-2一下 （来自原厂的资料）
详细说明了每个波段的增益和测量数据情况。
technical discussion
the superantenna field yagi is a 2-element driver-reflector yagi. on 10 and 6 meters, it uses full length elements with wide spacing to provide very wide-band coverage. in fact, it covers all of these two bands. on 12 and 15 meters, the elements are loaded at specific points along their lengths with 3.5 ph coils with an estimated q of 200. on 17 and 20 meters, the elements are loaded at specific points with 7.0 ph coils, again with an estimated q of 200. the estimatd power limit is 1kw
the field yagi is designed to use the fewest possible parts and still provide coverage of 6 amateur bands. second, it is designed to fit into the side-to-side space of a 10-meter yagi. third, the antenna is designed to be light weight and fit into a 36" long carrying case for easy of transport. finally, the antenna is designed to require no matching network that would further complicate antenna set-up procedures. these requirements for field use of the antenna together result in a compromise electrical design that provides considerable variation in forward gain and front-to-back ratio. however, the antenna is capable of forward gain that ranges from adequate to the equivalent of a full-size 2-element yagi, depending on the band. the front-to-back ratio will exceed 10 db at the optimum tuning point, but will vary from the peak value at a rate dependent on the amount of antenna loading used: the higher the loading, the more rapidly the front-to-back ratio decreases away from the design frequency.
nevertheless, the combination of forward gain, front-to-back ratio, and the ability to point the antenna at your target will result in improved performance over fixed doublets; base-loaded, mobile, and other vertical antennas; and single loaded dipoles of the same element length, even when the field yagi is as low as 20' above ground, the minimum recommended height on frequencies below the 10-meter band.
the following band-by-band notes are designed to provide you with reasonable expectations of the antenna on each band, as well as some guidance in making adjustments to optimize performance on a favorite operating frequency. for each band, there is a set of curves for gain, front-to-back ratio, and 50-ohm swr for the antenna when 20' above ground and when 1 wavelength above ground. you should expect that as you lower your operating frequency, the differential will be greater. for example, the difference is greatest on 20 meters, but non-existent on 6 meters, where 20' is roughly 1 wavelength.
6 meters: because a wavelength at 6-meters is roughly 20', only one set of performance curves is necessary. the gain curve is typical of a 2-element driver-reflector yagi with wide spacing. the wide spacing is needed for full-band coverage and because the 3-part boom will close only so far. the gain descends across the band, and the 180º front-to-back ratio peaks at 11 db near the lower end of the band, where most cw and ssb activity will be.
the swr curve is very flat, but does not go to 1:1. the swr level results from the element spacing, which yields a resistive component to the impedance of 55-90 ohms. closer element spacing would lower the average swr level by bringing the resistance nearer to 50 ohms, but performance would not otherwise change noticeably.
10 meters: on 10 meters, the yagi is also full-size, with no element loading. on this band, we begin to see the difference that height makes in yagi performance. with an elevation angle of 23º, the 20' high antenna shows nearly a half-db lower gain than the antenna at 1 wavelength (about 34.5') and an elevation angle of 13º. as well, the lower antenna has 1.5-2.0 db lower front-to-back ratio than the higher antenna. lowering the height to typical field-use levels displaces the front-to-back peak. the gain at the high end of the band is certainly usable, although one might wish to shorten the elements slightly if upper 10-meter am operation is often used. otherwise, the recommended settings yield good 2-element yagi performance across the band. indeed, the values of gain and front-to-back make a good example of standard full-size 2-element yagi performance for antenna heights of 1 wavelength and of 5/8 wavelength.
the 50-ohm swr performance for the array is almost ideal, with a feedpoint resistance range of about 40 to 65 ohms at either height. the broad swr curve for the wide 10-meter band results in part from the element spacing, about 0.16 wavelength. height does make a slight difference in the feedpoint reactance, which creates the slight shift between the 20' and 1-wavelength curves. nevertheless, the field yagi should require no adjustments with changes of height above the 20' level.
12 meters: 12 meters employs 3.5 ph loading coils part way out each element. loading coils have two consequences. as the 1-wavelength gain line shows, a loaded driver shows less gain than an unloaded element (for example, the 10-meter gain at a height of 1 wavelength). however, a loaded reflector increases the peak front-to-back ratio beyond the level available on a full size driver-reflector yagi.
the gain and front-to-back graph also shows the increasing penalty of using a low height. 20' is now about 1/2wavelength above ground. the 20'-gain (with a 26º elevation angle) isabout 0.8 db less than at 1 wavelength(with a 13º elevation angle). the 1-wavelength height front-to-back peaks within the passband. the peak front-to-back ratio for the 20'-high antenna is actually higher, but its peak is below the low end of the band due to the necessity of providing amatch with 50-ohm cable.
as the 50-ohm swr graph shows, the 2 swr curves are not significantly different. the feedpoint resistance varies between 33 and 40 ohms, since element loading reduces feedpoint impedance and the element spacing is restricted to about 1/8 wavelength. nonetheless, the field yagi on 12 provides good gain and directivity, even at 20' above ground.
on 15 meters, the field yagi uses the same 3.5 ph loading coil as on 12 meters, but with longer elements. hence, the loading is less, and this fact shows up in the relative gain and front-to-back curves. only the cw-end curves are shown in the graph, since the ssb curves are virtually identical, but displaced about 0.25 mhz up the band. the peak gain at a 1-wavelength height is slightly higher than for the 12-meter arrangement. (however, do not compare the rates of change of the two curves, since 15 meters is 4.5 times broader.) as well, the increasing reduction in gain at 20' is evident, since the 15-meter yagi is only 0.43 wavelength above ground.
despite these facts, the beam shows considerable gain over an equivalently loaded dipole and very good directivity-at least for half the band. the low values at the upper end of the band give ample reason to have a separate set of 15-meter ssb element measurements.
on 17 meters, we introduce the large (7.0 uh) loading coils to the elements, and the 1-wavelength (about 54’ on 17 meters) gain curve for the band shows that we lose about 0.5db further gain relative to the smaller loading coils (for example, on 12 meters). as well, since 20’ is only 3/8 wavelength above ground (resulting in an elevation angle of 34 degree for maximum gain), we lose additional gain relative to the value of 1 wavelength. however, the yagi still retains good gain relative to an equivalently loaded dipole of the same element length at the same height. the front-to-back ratiodoes not vary much between the two heights, although the curve is fairly steep due to increased element loading. th adequate front-to-back ratio provides the yagi with good direcetivity, even as gain drops due to loading and a low height when used at 20’. on this band, it is fairly easy to increase the driver length too much relative to the reflector length in the pursuit of a lower swr-with the consequences of reversing the pattern.
20 meters: on 20 meters, the elements are loaded with 7.0 ph coils and are slightly less than 0.1 wavelength apart. the result is a yagi with fairly narrow-band characteristics and lesser gain, even when examined at a 1-wavelength height (nearly 70' on 20 meters). as the graph shows, the front-to-back ratio has a high peak and a very rapid descent. only the cw curves appear, since the ssb curves are identical, but displaced by half the overall width of the band.
at a field height of 20, we suffer additional gain losses and a high elevation angle 0f 44 degrees, although the vertical beam width is sufficiently wide to provide good power and reception in the vicinity of 20º above the horizon. as well, over a span of about 100 khz, the front-to-back ratio is high enough to provide quite usable directivity. nonetheless, the performance of the beam on 20 meters leads to 2 recommendations: one is to use as much height as is feasible, and the other is to develop precise element length settings for one's favorite frequencies.
the swr curves for the field yagi are deceptive, especially the curves for a height of 1 wavelength. it appears that one might cover the entire band with a single set of element lengths. the full-size 10-meter element-provide narrow-band performance curves and require considerable care when setting up the yagi for use. with the elements spaced about 0.1 wavelength apart, the feedpoint resistance ranges from 27 to 50 ohms across the band and rises only to about 37 ohms within the half-band recommended operating range for each of the two settings in the tables.
these notes have surveyed the operating characteristics of the field yagi in order to give you guidance for special set-ups, reasonable expectations regarding performance, and complete candor relative to claims made for the antenna. the performance curves are derived from nec-4 models used in the design of the antenna and confirmed generally by performance tests that yielded the final recommendations for element dimensions. all performance tests employed a w2du ferrite-bead-choke balun (available from the wireman, inc.) to suppress common mode currents-a wise precaution for any antenna with a balanced feedpoint.
if you wish, you may use the field yagi as a dipole. first, remove the reflector element and shorten the boom to the 6-meter setting. the remaining driven element is light enough for the boom to support quite easily. the element length settings for dipole use will be slightly longer than the listed driver lengths. simply adjust the tip rod lengths for the lowest swr and operate.
relative to other types of antennas generally used for multi-band field operations, the superantenna qrp field yagi provides a combination of gain and directivity that will enhance most operations in a package that permits relatively simple band changing and easy transport to and from the operating site. with proper maintenance, the field yagi will give many years of solid service.
