Log Periodic Dipole Antenna


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By Marius Rensen
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For a long time, Ham operators were mostly active only on the classic short-wave bands 3.5 / 7 / 14 / 21 / 28 MHz which bustled with activity. Such Ham stations usually contained a quite modest antenna installation. For 3.5 and 7 MHz, the European operators used a W3DZZ Dipole, which also could be used on the higher bands. For 14 / 21 / 28 MHz, the 3-band-Dipole YAGI beam was used commonly. These antennas usually did the job for most Hams. Only antenna enthusiasts and DXers had a more impressive antenna site. With the entry of the WARC - bands 10.1 / 18 / 24.9 MHz, new antennas were needed. The Log Periodic Dipole antenna (LPD) has come to the attention of many to help in this regard.

As a SWL and utility listener, I had a lot of antenna eXperimentations with dipoles, Windom, T2FD, long wire, active antennas and so on, but I had never an broadband antenna with such excellent results as the log periodic. The LPD has been  preferred by commercial stations since the beginning of the 1960s. The antenna pattern, the forward gain and the SWR of these broadband antennas work whole operating range almost without equal. Due to construction problems, dimensions, pricing and the total weight of the LPD for the short-wave bands, only a few Ham operators and SWLs used a Log Periodic in the past.

However, in stepped the German company Titanex with a new, well reasoned solution for this type of antenna. The strong rods from the aluminum-Titanium-alloy, form a very stable frame construction design from which the (wire) LPD Antenna array is stretched.

The DLPD 15 is a log periodical dipole antenna with 15 elements made with state-of-the-art technology. The frame is made from Aluminum-Titanium alloy tubes (picture 1), which are harder than steel, but as light as aluminum. The fabric is made from Kevlar rope and high-grade steel wire and are resistant to the elements and windloading. Also, the installed isolating parts from Glasfiber plastic withstand all demands necessary. Every wire dipole is stretched between the isolated ropes. The isolating ropes are manufactured from Kevlar and coated for UV-protection with Polyester.

The DLPD 15 is designed for 14 to 30 MHz (picture 2), and a tuning radius of 5.50 m. Titanex has also designed, in the free part of the frame, a 10.1 MHz (picture 3) and a 7 MHz (picture 4) half-wave dipole. So, you can use the DLPD 15 from 7-30 MHz, but with construction dimensions as from a 14-30 MHz LPD. The DLPD 15 has 11 elements for the LPD array 14-30 MHz (picture 5), 2 elements for 7 and 10 MHz, and two reflectors for the 15 and 20 meter (picture 6) bands. Thus, the explanation for the name "DLPD 15," DLPD which means Draht (Wire) Log Periodic Dipole with 15 elements.

The above drawings are copyrights of Titanex!

Other Specifications

Weight: 22 Kg; Boom length: 6 m + 2 m; 14 to 30 MHz: 11 elements; Longest element: 10.2 m; Shortest element: 3.54 m; Other elements: 40 meter & 30 meter band; Reflectors: 20 meter & 15 meter band; Forward Gain: 14 - 30 MHz 6.5 dBd; 7 MHz 1 dBd; 10 MHz 2 dBd; Front to Back Ratio: 20 dB from 14 MHz - 30 MHz; SWR: Typical 2:1 on all Ham Bands; Tuning Radius: 5.5 m; Wind Load: 40 Kg.
Price of the DLPD 15: DEM 2365 incl. 15 % VAT (US$ 1350 - VAT)

All of the main parts (437) arrived in two 6 m long cardboard tubes with the alu-titanium tubes, and one other package containing the small parts. First, I had to chop down one of the trees in my garden to make the needed space (11 x 8 m) for the construction place (picture 11). The complete assembly requires about 3-4 days and you must work exactly as illustrated, double-checking everything before going to the next step. The construction manual describes all details step by step with a lot of drawings, photos and a parts' list. All parts in the drawings are numbered, so you must continually refer to the parts' list.

All elements are clamped (picture 7) on the boom tubes. Nothing is soldered or screwed, which is a very good construction idea for optimal electrical contact. Thirteen aluminum winches (picture 8) are used to balance the whole antenna construction and for fine tuning of some of the dipoles. All parts, such as the element wire, clamps and so on are high-grade steel. The DLPD is direct-fed without a balun (picture 9), with RG 213 U cable running from the shortest element inside of the boom (8 m). Then the cable runs outside of the boom, back to the middle of the boom and down to the mast into the shack.

The 7 and 10 MHz dipoles are fine-tuned using aluminum winches and a SWR meter. I have measured the LPD (14-30 MHz) array and it has a typical SWR below 2:1 on the whole frequency spectrum. As the DLPD 15 is a real "lightweight," it was not a problem to mount the antenna with help of my two sons on the mast and the Creatix Rotor (picture 10). It is a lot of fun to construct such a antenna. Also, it is very interesting to see the mechanical construction details for such a "big" antenna.

After completing the whole antenna installation and connecting to my NRD 525 receiver, I was very curious about how well it works. I have make some tests to check the difference between my old T2FD, a 15 m wire with a MLB and the new DLPD 15. Hear it for yourself by clicking on this wave file: 

Load Wave File

As a radiofax enthusiast, I have tested different facsimile stations with the antennas, especially stations transmitting on the higher frequencies above 10 MHz. At all times I received a better and clearer signal with the DLPD 15. Some stations, such as Fishery Radio (J) and VNA Vietnam was received only with the DLPD 15 and no signals were heard on the other antennas. The beacon signals on 14.100 to 28.200 kHz from South America, were only heard with the DLPD 15. For facsimile and SSTV, I now receive much better pictures from DX stations and the pictures do not have so many garbled lines as with the other antennas. Plus, now I can receive SSTV stations just as a particular Ham operator here in Europe does with his YAGI beam. In the past, I was wondering why I could not hear his QSO partner. This antenna works fine down to 2 MHz, but there, the other antennas are sometimes as good or better than the DLPD 15.

Overall, the DLPD 15 has a excellent signal/noise ratio and is what I prefer as a facsimile/SSTV enthusiast. (example from Darwin Australia 13213 KM from my location in Northern Germany)

Marius Rensen Location Hannover, Germany 52.27 N 09.41 E (100116.2632@compuserve.com) http://ourworld.compuserve.com/homepages/HFFAX

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Last modified: March 23, 2005