WELCOME TO YU7EF ANTENNA GALLERY 

 

 YU7EF 144 MHz LOW TEMPERATURE ANTENNAS  

Since a large number of radio-amateurs has shown interest in my antennas after basic characteristics were published in VE7BQH G/T chart, and I am not able to answer numerous e-mail requests for data, I have decided to publish the complete data and make them available for all those willing to build and use my antennas.  

During the design of these antennas, the main focus was put on obtaining an as low as possible isotropic temperature of the antennas and as much as possible gain for given boom length resulting in best possible G/T ratio. From all of these antennas would be possible to get some more gain with sacrifice of temperature, bandwidth or poor impedance. All antennas are optimized for pure 50 ohm feed impedance with minimum possible reactance to avoid need for some of specific feed solutions and impedance transformations such as Gamma Match, T-Match, Hairpin etc. This way all antennas have very low internal loss and very good efficiency.  

Antennas up to 3 WL are mostly designed as width band designs, having in mind that they can be used as a single antenna for the majority of average users for every day use, by covering 144 – 146 MHz with reasonable SWR. Longer antennas, however, are designed for a rather narrow band as I would not expect someone to build a 4 or 5 WL antenna to use it for FM, but only for „low signal“ communications such as tropo DX, MS and EME at 144.0 – 144.5 MHz.   

For every antenna there is a table of FREE SPACE dimensions for elements diameters of 4, 5, 6, 8 and 10 mm – sizes most used. Note that the driven element size is 10 mm in ALL cases and it is for OPEN DIPOLE. As it is obvious from specifications, the use of larger element diameters is recommended due to better specifications (lower internal loss and better efficiency) but also  because of better mechanical strength, much more resistance to bending and damage by wind, ice and particularly birds. Difference in weight of the antenna with 5 mm wire elements and the one with 8x1 mm tubing is insignificant and one would not get anything but a mechanically weaker antenna. My recommendation is to use the 8 mm tubing whenever possible for best results.  

Depending on boom diameter used and type of element mounting, the element lengths from the table need to be corrected accordingly. Boom correction by DL6WU formula has proven to be reliable over the years and the attached table shows the correction values for wide range of boom sizes commonly used by hams.  

For every antenna, the tables show basic antenna specifications as well as recommended E and H plane stacking distance for best G/T ratio. With these stacking distances, a 4 yagi bay stacking gain is generally about 5.9 dB compared to a single antenna and with first side lobes down to 11 – 12 dB. It  is recommended that the stacking distance should be kept from -10% to +5% of the optimum spacing for best results and acceptable degradation of gain, temperature and G/T ratio of the system. With every antenna there are also attached single antenna H and E plane radiation patterns.    

Be noted that Ta and G/T values in my tables are a bit different from values shown in VE7BQH chart. Values in VE7BQH chart are all calculated with „Yagi Analysis“ 3.54 that has tendency of small error, making results more optimistic, probably from not taking in account material elements loss, while all values for Ta and G/T in my tables are calculated with program TANT by YT1NT which is more precise – particularly when calculating values for a 4 yagi bay. All values for Ta and G/T are calculated for antennas elevated at 30° as recommended by DJ9BV and as it is in YA program

My recommendation is to always build antennas with INSULATED elements THROUGH the boom since such a way of construction is a good guarantee for many years of reliable operation of the antennas without change in performance.  

Even though driven element length in tables is given for open dipole, my recommendation is to build antennas with folded dipole due to many advantages compared to open dipole, except simplicity. With folded dipole all you need is the use of classic WL/2 * k, 4:1 coaxial balun.  

Construction tolerances need to be kept as low as possible and by all means should not be more than 1 mm while tolerance of ±0.5 mm will give you perfect results and calculated specifications.  

Special attention should be pointed to spacing measurement, and it always has to be done as shown in the table - cumulative. Never calculate separate spacings and measure it that way since any measuring errors will accumulate and you will end up with an antenna that is not what has been designed and expected.  

A large number of these antennas has been built and used by hams with excellent results.  

For any further questions and information feel free to contact me on my e-mail :

  pop@yu7ef.com  

I would appreciate any feedback about Your experiences and results as well as pictures, to be used for future projects and possible corrections and modifications on existing designs.    

SPECIAL NOTE:  

All these designs are the result of many years' hard work and they represent the intellectual property of the author. Distribution and publishing of these data and information is permitted ONLY for radio-amateur purposes and construction. Use of these information and data for any commercial purposes is strictly prohibited without the written authorization of the author.

Ljubisa Popa

YU7EF