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RE-A144V58/1

By ON6MU

 

 

L'antenna 5/8 d'onda

 
In VHF, le antenne piu' usate sono le 1/4 l'onda e le 5/8 d'onda; le seconde hannun guadagno di circa 3db sulle prime.

La figura seguente riporta la distribuzione delle correnti  per entrambe le configurazioni.

Un'altro pregio della 5/8 d'onda  è quello di ottenere un angolo inferiore di radiazioni.

Svantaggi:

 richiede un dispositivo adattatore alla base di abbinarlo al coax, non può essere collegato direttamente.

Questa antenna ha circa 1,2 dB di guadagno rispetto  l'antenna dipolo e la 1/2 onda verticale.

 

 

Parts list

• Type 1:

• alu or copper tubing of 1 meter 15mm tube and 1 meter 12 mm diameter tube

• 3 times 5 mm alu or copper tube of 22 cm

• 1 female PL 259 chassis

• some silver wire of 1 mm

• A robust PVC box of approx 30x50x18 mm and 1,5mm or more thick

• a piece of hard insulating material that snuggly fits inside the base tube, like:
  fiberglass, nylon, hard pvc, hard wood, bamboo etc... as long as it's very strong, stress and weather resistant.

• and a few innox hose clamps
  

• Type 2:

• alu or copper tubing of 1 meter 15mm tube and 1 meter 12 mm diameter tube

• 3 times 5 mm alu or copper tube of 22 cm

• +- 30 cm 2,5mm electrical installation wire

• a piece of hard insulating material that snuggly fits inside the base tube, like:
  fyberglass, nylon, hard pvc, hard wood, bamboo etc... as long as it's very strong, stress and weather resistant.

• some 50 ohm coax

• and a few innox hose clamps
  

Note: there are many ways to build your antenna and I'm sure some can come up with better mechanical designs then described here although the design and material used here is cheap and easy to find. 
Both types of 144 Mhz 5/8 wave antenna's described here has the same radiationpattern and gain, but type 2 has the advantage of being electrical (and DC) grounded and can disipate more power.

 

The antenna:

- saw the 1 meter 15 mm alu tube in half. One part (50 cm) will be used as a boom and the other as the first part (also 50cm) of the antenna.
- saw some grooves (approx 1,5 cm) in the both halves of the tube to allow a hose clamp to tighten everything up.
- the 1 meter 12 mm alu tube is fitted inside the 15 mm base tube and can be hold tight with a hose clamp. Measure from the base up 1,3 meters. You can alwyas tune the antenna to its best SWR by sliding the top tube in or out.

 

 

• - saw a piece of that hard insulating material of your choice and fit it 10 cm in the antenna and boom part and leave a gap of 3 mm between them.
  - hammer down one end of each of the 3 radials ( 3 x 22 cm) so it becomes a bit flatten. This will make things easier to screw tight with the hose clamp. These radials are fitted on the boom section.
  

• The coil:
  
  Wind 3,2 turns of silver plated copper wire of 1mm thickness with an inside coil diameter of 8 mm (outside 10mm) and a the coil has a little spacing of approx. 0,2 mm.

• Connect the coil to the antenna and the other end to the centre of your 50 ohm coax cable.
  I used a little plastic box where I placed the coil and the PL connector.

 

Specifications antenna type 1
RE-A144V58/1

• centre frequency: 145 Mhz

• bandwidth: 2 Mhz

• maximum tunable frequency range: 142...150 MHz +-

• impedance: 50 Ohms

• Gain: 4,1 dBi

• maximum power using described components: 150watt +-

• heigth: 1,25 m

 

The antenna type 2
RE-A144V58/2

• The antenna:
  - saw the 1 meter 15 mm alu tube in half. One part (50 cm) will be used as a boom and the other as the first part (also 50cm) of the antenna.
  - saw some grooves (approx 1,5 cm) in the both halves of the tube to allow a hose clamp to tighten everything up.
  - the 1 meter 12 mm alu tube is fitted inside the 15 mm base tube and can be hold tight with a hose clamp. Measure from the base up 1,3 meters. You can alwyas tune the antenna to its best SWR by sliding the top tube in or out.
  - saw a piece of that hard insulating material of your choice and fit it 10 cm in the antenna and boom part and leave a gap of 3 mm between them.
  - hammer down one end of each of the 3 radials ( 3 x 22 cm) so it becomes a bit flatten. This will make things easier to screw tight with the hose clamp. These radials are fitted on the boom section.

• - Fit the braid of the 50 ohm coax to the boom section
  
  

• The "ringostar" based coil:
  Is made out of 26 cm of 2,5mm installation wire. Remove the isolation of the wire and tin with a soldering iron the entire wire. The coil is 1,2 turns and has a diameter of 5 cm. One side is connected to the antenna and the other side to the boom.

• Find the 1:1 SWR position of the connection the centre of your coax should be soldered to. Half way the coil is a good place to start. Be sure your antenna length is measured up to 1,25 m. When you found the "sweat" spot solder the the centre to the coil. You can alwys fine tune the antenna for best SWR by sliding in or out the top tube of the antenna.
  
  

Specifications antenna type 2
RE-A144V58/2

• centre frequency: 145 Mhz

• bandwidth: 2 Mhz

• maximum tunable frequency range: 143...149 MHz +-

• impedance: 50 Ohms

• Gain: 4,2 dBi

• DC grounded (no static buildup)

• maximum power using described components: 250watt +-

• Height: 1,25 m

Be sure to seal everything up to avoid moisture, corrosion etc...

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