Half-wave Vertical with Collins-Filter (50+70 MHz)
A 70-MHz-Version by OZ2M see down!
Bandwidth > 1.3MHz for SWR < 1.5, Gain 20 m above ground 3,7 dBd at 4°
This antenna is very useful for receiving or scanning purposes, but you can use it for transmitting, too. It is 2,94 m long and has a pi-configuration (Collins-Filter) for the matching.
It is mounted on the top of my tower, you will find a place for it too, I am shure.
The rod is made of 16x1.5 mm, 12x1 mm and 10x1 mm Aluminium, the length is not citical. I have used 2,90 m and a piece of wire to connect it to the matching circuit in the box. The small C's handle 100 W RF without any problems!
The gain is 0 dBd (free space), but 20m above ground with medium conductivity you can reach 3,7 dBd. I have plotted the elevation pattern below.
The signals are sometimes as loud as on my 6-El-Yagi (ES), most of the time about 1-2 S-units lower. For real DX the Yagi outperforms the vertical of cause...
But I find signals outside the Yagi-direction, which I would not have heard with the wrong position of the Yagi!
Important: The matching circuit must be tuned at the final mounting place!
C1: Variable Mica-Capacitor 150pF
C2: Variable Air-Capacitor 20pF
L: 6 turns 1.5mm wire, inner diameter 12mm
The pictures show the construction better than a lot of words...
Elevation plot 20m above ground, gain 3,75dBd at 4°
70-MHz-Lambda/2-Vertical (built by OZ2M)
This Vertical was built by Bo, OZ2M
The matching circuit is the same as above with the following components:
C 1 = 20 - 110 pF, variabel Mica capacitor
C 2 = 2 - 15 pF, variabel foil capacitor
L 1 = 5 Turns, 1mm Cu with 10 mm inner diameter
The length of the radiator is 2,13 m (uncritical diameter)
The same vertical is running as a beacon antenna at OE5MPL.