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LOGI LOW FREQUENCY MODIFICATION
If your radio system requires DC isolation or you plan to use your Logi below
900 MHz, the small connecting traces near the rear of the antenna should be
cut. By removing these traces you can extend the effective frequency range
down to 825 MHz. You will however
wind up with some 'lumps' in the
Soldered Coax Positioning
matching response on the high
frequency end.
BUILDING A CORNER REFLECTOR
Corner reflector antennas have long
been used by the Military and Radio
Amateurs for high forward gain
applications like field data links. Using a
properly sized 90° angle corner reflector
will typically give you a 10 dB gain or
higher over that of a stand alone dipole
antenna. The construction of a traditional corner reflector is very simple. Two
plates are connected at a 90° angle with a feed element, usually a dipole,
positioned along the vertex at the angular focal point of the plates. The
dimensions of the reflector plates are luckily not critical (within reason of
course) and the frequency characteristics are much better than most other
parasitic arrays with the same gain rating. One drawback of the normal corner
reflector arrangement is the fact that the active (radiating or receiving) element
is usually a narrow bandwidth dipole. In our case, we suggest using the
'broadband' Logi as the feed element. This gives you the same corner reflector
benefits but without the normal narrow bandwidth limitations!
With the wealth of information available today on the Internet, countless articles
and design schemes can be found covering the construction of corner
reflectors. The main difference from the norm is the use of the Logi as the main
element versus a simple dipole. The following diagram gives a few basic
dimensions for an experimental corner
Final Installation View
reflector. The main points to key in on are
the base reflector size and the element (the
Logi) placement for proper broadband
coverage.
Different types of materials can be used to
form the reflector plates. Any type of
perforated aluminum or copper sheet will
work well. Small holes in the material help
to cut down on wind resistance. The overall
reflector length and width sizes should be
chosen to properly work at the lowest
LPY2 • 6
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