DSFO432-25
The DS432-25 is a high performance K1FO yagi antenna design. The idea was to design a yagi that delivered great performance at 432 MHz, but in a size that did not require boom supports. This 25 element yagi utilizes a 17' 4" boom with rather large diameter tubing, 1 3/8" in the center, and tapering to 1 1/4" on each end. The final product is very rugged and will stand up to any ice storm or high winds you may encounter. We have a photo of a 4 yagi DSFO432-25 array with 4 1/2" of ice covering it. The boom hardly sagged! The DSFO432-25 is supplied with a T match feed and type N connector 50 ohm input connector. The mast clamping arrangement utilizes a 3" x 5" extruded plate and is attached with stainless steel u-bolts.. Mast size may be up to 2' diameter. This design has been carefully checked out in the real world to ensure peak performance.. This antenna provides 16.5 dBd maximum gain up to about 436 MHz, and will provide great performance between about 428 to 438 MHz. A higher frequency response peak is needed for good wet weather performance on higher frequency yagis, and our choice has netted a design that is remarkably stable in wet or dry weather. Forward gain, wide bandwidth, and exceptionally clean patterns are the most notable characteristics of this antenna, as with all of the K1FO style designs. The net result is wide beamwidth, and a clean lobe structure coupled with a very high gain figure. Clean H-plane patterns translate to efficient stacking with maximum possible gain and manageable array sidelobes, should you wish to stack these antennas in a larger array.
All Directive Systems antennas are verified for proper performance on an antenna range with state of the art swept measurement equipment to record the results. Some performance curves have been provided below on these pages below. You can also download the instruction manual in PDF form.
DSFO432-25 YAGI ARRAY photo by WW1M
To evaluate the bandwidth, click here. To look at return loss (VSWR), click here.
Note that the graph depicts return loss rather than VSWR. As a reminder, remember that -14 dB return loss is equal to a 1.5:1 VSWR and -9.5 dB return loss is 2:1. Anything below -20 dB signifies an ultra flat match. Your wattmeter will act like it is not connected to anything when viewing such reflected power levels. You can adjust the T match to favor a particular frequency if you wish. These curves are the factory settings as published in our instruction manual.
For more information on setting the T match, check here.
The DSFO432-25 specifications are listed here. PDF Format
The DSFO432-15RS yagi employs a traditional modified T match and half wave balun to match your 50 ohm feedline to the driven element. The T match and half wave balun provides a great method for achieving proper match along with exemplary decoupling of the feedline from unwanted antenna currents. At these higher frequencies, gamma matches and other matching methods used on lower frequencies, start to behave erratically. They tend to unbalance the feedpoint and cannot provide an effective rf ground as a result. The result is poor decoupling of the feedline and the antenna boom itself! Poor decoupling effects can reduce forward gain by large amounts. If any power flows on the outside of the coaxial cable, or along the antenna boom, gain or efficiency suffers drastically. Poor decoupling will show up as varying VSWR as the feedline is handled. Deep response nulls within the passband of the yagi are a tip off as well. Any skewing of the main lobe off the boresite heading indicates out of control rf currents caused by poor (or no) decoupling.
A sample close up of a typical Directive Systems "T" match is shown here. The actual antenna shown is a shorter rear mount 11 element 432 yagi (DSFO432-11R) driven element, but it is quite similar in appearance to the DSFO432-25.
SAMPLE DRIVEN ELEMENT T MATCH DETAIL
The DSFO432-25 computer modeled patterns are here:
