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It says in their datasheets to connect a 50ohm, 1/4 wavelength antenna to them. The length of the antenna is easy to calculate, but how can I calculate the impedance of the antenna? Are the specs of the antenna even critical for short range use? The transmitter boasts 1km of transmitting range, say I only need 100 ~ 200 meters.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
A quarter wave monopole above a groundplane naturally has an impedance around 50 to 70 ohms. So if you make a piece of wire a quarter wavelength long and stick it into the antenna socket, the transmitter will see an impedance somewhere around 50 ohms and it should work.
If you want the antenna some distance away, use 50 ohm coaxial cable to hook it up.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Some times there can be problems at close range so if you have problems when testing them they still might work fine at long range. Antennas can be a very tricky subject at close range, so can cheap receivers.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Thanks for the tips.
The receiver generates a lot of noise with no signal, and being AC coupled I can't send a continuous signal to keep the output steady. My earlier IR decoder has proven absolutely hopeless as it measures pulse length once per pulse. It doesn't take much noise to ruin the signal then. What would be the best way to transfer data over a noisy link? Should I attempt Manchester coding or is there a better way? Or can I filter out the noise somehow?
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RF modules
