viernes, 10 de julio de 2020

"Blandiblu" 2m portable yagi antenna

Blandiblú v2 design working at Sollube Mt EA2/BI-033
 The goal of the project was to make a light and portable antenna for the 144-146 MHz band.  The design of reference was the great IZ2UUF 100 gr. yagi, but I chose to make the elements of brass, to be able to solder them later. I don't like aluminium. Although it can be lighter, it's harder to work with. The antenna is a 50 ohm 4 elements vertical yagi with non conductive boom.

So, here we go. I found some sort of 25 mm aluminium wire, teoretically covered with a thin copper layer, that later shown not to be able to be soldered at all. After the first try, the elements were so soft that they bent too easily. It wasn't the right material at all. The name of "blandiblú" comes from here (you can search its meaning on the web to find why).
Blandiblú ver. 1 antenna with aluminium "interactive" elements
The boom, from the very beginning, was a 1 meter piece of a broken fishing rod, formerly used as SOTA mast. I have 3 of them, so more designs are to come for sure.
The elements, finally, were 4 x 1m length, 4mm outer diameter, 0.25mm thickness brass rods, which are available at local bricolage stores. They make a good compromise between weight and strength. 

The lengths and positions of the elements were brought from IZ2UUF website and are (all measures in mm):

ElementLengthPosition
reflector10100
driven995460
1st director900660
2nd director840990

The key parts of the antenna were two: the boom_to_mast adaptor and the feeding_point of the driven element. They were made with a 3D printer (this is the worst part of the design, not everybody has easy access to one). I designed both using Wings3D free software. Here they are:

boom to mast adapter

driven element feeder (1)

driven element feeder (2)
The 4 mm wide brass rod were drilled to allow 2 x 2mm diam x 10mm length screws, which will later connect the center conductor and the braid of the coaxial cable to each side of the driven element. I used a total of 6 meters of RG-174 from antena to rig. 
The same coaxial wire is also used to make a choke. This is made of several turns of the coaxial with a length of about 34,5 cm. The number of turns may vary depending of the diameter of the boom, just keep that length. Tape it later to the boom and drive the rest of the coaxial back until it falls behind the reflector. Keep it perpedicular to the driven element.

The elements "hang" on the boom, so they are not vertically aligned with it. The size of the feeder will give you the amount of deviation. Being of brass, I soldered small pieces of copper wire to set them in their possitions.

boom to mast and elements set details
 

The holes must be carefully made to mantain the same orientation along the boom. IZ2UUF gives a well explained procedure about how to make this right.

The antenna was first tested on tuesday from Sollube Mt. SOTA Ref EA2/BI-033, and the results were apparently good, making several long distance QSOs. Later this week I will try to use it from other "rf noisy summits" around my home.

Finally, this and other alternative designs were tested using free antenna design software MMANA-GAL. The results obtained are more or less coherent with the actual developement.

I hope all this would be useful to SOTA VHF adicts. See you on the air!

73, Mikel EA2CW

Useful references:
IZ2UUF 100 g portable yagi
A lot of information on yagi design by DK7ZB (and alternative 4 el short 50 ohm yagi design)
On-line yagi calculator
VK5DJ yagi design software
Wings 3D easy and free software
MMANA-GAL free antenna design software

lunes, 24 de junio de 2019

Probando la antena K1POO OCFD (Off Center Fed Dipole)

Todas las fotografías de Marcial, EA2WX

lunes, 27 de agosto de 2018

CW. Empezando con los QSO

Cuando adquirimos una velocidad suficiente recibiendo en telegrafía, llega el momento de ponernos a hacer QSOs en CW.
En las bandas hay un montón de operadores -con mas o menos experiencia- y para "entrar a jugar" debemos saber cómo ha de hacerse, para evitar molestar al resto de colegas.
En esta entrada queremos dar unas cuantas pautas para intentar hacerlo lo mejor posible. Allá vamos!