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Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
I'm completing the final stage of my wireless wind generator monitor station. After finishing adjusting on the encoding and procol (with checksum control) the thing works pretty well. With the antenna(s) disconnected the data is transmitted accross the room without signal loses (there is a small marker on the output LCD to check connection status). The modules are connected to a PC mount BNC connector. The antennas are small automotive 17cm antennsa with screw terminals connected to a BNC male connector by means of a coaxial cable (those with little diameter). When i connect the antennas the signal gets unstable and choppy. I'm not an RF expert, probably something (maybe the coax cable) is attenuating the signal, or the gain is too high and the receiver gets fooled by the reflections of the wall.. Anyway anyone has some suggestion how to optimize it? (the project is in the projects section)
Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
Are the antennas resonant at 433.92MHz? Do they need a ground plane to function properly? Judging by the length (which is 1/4 wavelength), you will need a ground-plane or a set of 1/4 wave radials to make the antenna work properly. If the coax is less than a couple of meters long, loss at this frequency should not degrade your signal much...(assuming something like RG-58 cable).
Also, I don't imagine that your data rate is so high that reflections will cause intersymbol interference...altho' indoor operating at these frequencies can produce deep fades in signal strength as you move around.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Automotive antennas will have been designed on the assumption that a substantial ground plane (the roof/metal bodywork of the car) is beneath them.
Without the ground plane, the antenna will present an impedance mismatch to the transmission line, and you may standing waves and unwanted reflections back into the transmitter.
If you are not to mount the antennas on a car, you will have to make a suitable ground plane, or make your own antenna - a simple vertical dipole, for example, if you want 360 deg radiation.
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Actually the sistem consist in: An antenna (no ground plane) connected by means of an RG-58 cable on the transmitter, same on the receiver. Signal strenght monitored by error counter averaged by five cycles.
Whithout antennas on both transmitter the range is low, (signal is lost in 10-15 meters indoors) With antennas the range is extended but probably not optimal , also when too close the signal degrades very quickly.
I don't have room for a real ground plane (the circuit will be contained in a waterproof PVC box mounted on a steel pipe, on which the generator is mounted). Can i use the tower as ground plane?
Regarding the receiver side, how should i proceed?
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Antenna design for wireless link (TLP434-RLP434)
