Thanks for the explanation of why the tri-boom was designed. For me, the layman, it makes sense. Televes DAT LR antennas are well-constructed. It's because of this I decided to take my hacking to a different level. First of all I don't have time to learn antenna modeling software so I try to make Intelligent Decisions I'm what I'm going to do and that's usually just to make my antennas longer. It does seem to work.Zombie thread for sure, sorry. I read that comment suggesting that a triple boom design has no benefit in a number of places in the forum, which probably needs clarification.
Apologize the obvious, but just to start from the beginning, to better understand the behavior of Televes antennas, it is necessary to first understand how a Yagi antenna works. A Yagi antenna has a driven element (dipole) and a series of passive elements (reflector and directors) that are electromagnetically coupled to the dipole and to each other, with an inductive reactance the reflector (that blocks the signal in its direction) and capacitive reactance the directors (that favors the reception of the signal in its direction). This causes the antenna as a whole to favor reception in the direction of the directors and prevent reception in the direction of the reflector. The very basics thus far.
Given the nature of the coupling, the effectiveness of the passive elements decreases with the distance from the dipole, which means that the elements furthest from it have much less influence on the overall performance than the closest ones. As you can see in the figure I'm pasting below just as a basic example, from the sixth element on, the influence of the directors on the overall gain is very limited, the first five elements raise the gain by approximately 8dB and the next five elements only add another 1.5dB approx. So past certain point, which depends on the particular design, there are diminishing returns in what a longer antenna buys you.
View attachment 11414
To improve the behavior of Yagi type antennas, Televes introduced more than 25 years ago the concept of several rows of directors stacked vertically, thereby achieving a greater number of directors close to the dipole, which allows to have higher perfomance antennas but smaller in size than conventional yagis.
As can be seen in the figure below representing the energy flow in an Ellipse antenna, the elements closest to the dipole are the most effective. With the vertical arrangement of the same we manage to have more elements near the dipole, increasing the performance of the antenna while maintaining a compact size.
View attachment 11415
However, this requires a careful redesign of the dipole that allows for very precise coupling in the vertical plane. A typical simple dipole does not work with this structure. While Televes antenna designs have been copied over and over again -down to the color- most still don't get this part right and then the advantage of the multiple directors is wasted.
Hope this helps clarify some of this, and again apologies for resurrecting this.
Here's the hack I made from 2 Televes DAT LR MIX antennas. On top is a 91XG with 163 elements:
Although it the reception isn't quite twice as strong because it's twice as large, the results were promising and effective:
Amazingly, the modified seem to be picking up the lower channels better at this particular time :
Here you can see the two antennas going head-to-head:
J.Ruano (or anybody else for that matter), do you think changing the angles of the upper and lower boom would have any effect?
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