MY TWINBOOM YAGIS FOR 50 MHZ
Here you can see my twinboom (double boom) yagi antenna models for 50 MHz. It is up to you to choose one of them to build. What is the twinboom antenna, you can find on my page "My twinboom antenna for 144 MHz".
When the 50 MHz band is considered, one thing is different regarding higher bands. That is noise. There is much, much more noise on this band, coming from all around, which makes low antenna temperature unimportant. However, I still insist on low temperature characteristics.
The basic favour of low temperature antenna is that energy is more concentrated in wanted direction. The main lobe, in this way, gives more gain or wider pattern. Therefore, noiseless reception (which is lost on 50 MHz due to high level of sky and earth natural noise) is not the only advantage of low temperature antenna.
Because noise characteristics are not important, Tsky and Tearth are omitted. Instead, I give the data of main lobe width
Here the twinboom antennas are placed into VE7BQH G/T table where they belong according to their length, so that they can be compared with antennas of different authors. You can see that the twinbooms are better for 1 to 2 dB (sometimes even more!) than the classic style yagis.
Some words about construction: Just look at the photo on my page http://www.qslnet.de/member1/yu7xl/my_tween_boom_yagi_antennas_for.htm
and everything will be clear. Both booms should be bent toward each other, following dimensions given for the particular antenna. A small error in bending is negligible, but positions of elements must be precisely marked on the central boom and, at right angles, projected on the upper and lower booms. For short antennas, up to some 7 meters length, booms can be made of tinny aluminum tubes (Ø25 mm). No fear, the construction will be strong enough. For longer antennas, use thicker tubes.
The radiator is in form of double rectangle. For every particular antenna, it is separately described. The joints should be welded or hard soldered. The impedance at the feeding points is 200 Ohm. You can bring a 50 Ohm coaxial cable to the feed points and apply a 1/2λ simetrizing baloon.
Finally, all elements must be isolated from the boom.
Note: KF2YN correction is applied on all my models. The formula should be applied because the antenna modelling software (NEC/EZNEC) does not contain the KF2YN formula and cannot fight off the convergence error caused by tappered or sharply bent elements. After applying, antenna data are standardized and can be put into VE7BQH table alongside with other competing antennas. Therefore, do not be confused with different results of gain in tables and in diagrams! This correction gives the real gain for ALUMINUM, and the correct data are shown in green fields. Except for gain, the differences in other parameters (F/B, F/S etc) are minor and can be neglected.