70cm Ground Plane Antenna
This little aerial was intended to make it easier for me to connect to
the local packet-radio digipeater and to work the various phone and multimedia
repeaters. Again the design was choosen as portable as possible. Especially
in combination with the glass-fibre mast, known from the other projects
on this page.
about 90cm of 1mm silver steel rod
one luster terminal with at least two
lead guides beeing able to carry 2mm leads
50Ohms coax cable
glass fibre mast
Construction & Design
Sketches or drawings are IMHO not necessesary because of the extreme simplicity
of the "design".
Cut 19cm off the rod, and bend 2cm at one end by an angle of 90°.
This will be the radiator, 17cm straight up in the air. It will directly
go in one whole of the luster terminal. Watch out, that the terminal´s
skrews are pointing downwards, elsewhise you will later have problems with
water and corrosion. The radials are made of two rods with a length of
34cm. Stick both through the other whole of the luster terminal, centered.
You might now bend each rod to an angle of 90°, with the luster terminal
in it´s centre. To give it the correct feed-point impedance the radials
should be twisted slighly downwards.
Connect the coax cable to your little aerial, using again the abilities
of the terminal. BTW, I used RG174 (lossy!) for the last meter, to reduce
In the middle of modern luster terminals there are wholes, to mount
the terminal wherever it should go to. This whole (3mm) is perfect to stick
the mast through. At the very top mine has a diameter of 2.8mm. This makes
the ground plane to rest only 12cm below the top.
In principle exactly the same way as for any other antenna, you have built
up to know. Find it´s resonance, and cut off as much as needed to
obtain the desired resonance frequency. The SWR can be improved by variing
the downward angles of the radials.
I am happy! Whenever the reflection I have to use with my indoor HB9CV-antenna
does not provide nice signals, I can errect the glass-fibre mast with the
ground plane, and establish a stable link to my local digipeater (running
the transceiver´s lowest power setting). Besides that I could hear
a lot more phone repeaters than before. The only pitty is, that I do only
posses one such mast... so, no shortwave during packet, or vica versa :-(
Taken at 31.12.2000, the last day of the second millenium... Various angles