3 Field test results

sh123 edytuje tę stronę 2022-12-19 11:07:57 +02:00

• Antennas
  • Client: rubber duck, halo, mobile antenna on a car roof
  • Server: 7 element UHF yagi indoors, vertical on the roof
  • ⚠ With such low power it is very important to have antenna SWR close to 1, many rubber duck antennas are claimed to be 433MHz, but they do not resonate at that frequency at all or resonate only when attached to its native large handheld transceiver, which has enough metal inside to behave as a counterpoise, these antennas have SWR 2 or higher. Check your antenna on antenna analyzer before using, add wire counterpoise if needed or better to use dipole or halo home made antenna for that matter
• Range (20 KHz channel width and 9 spreading factor, also got similar results with 125 kHz and 12 SF), it will mostly depend on your base station's antenna elevation
  • About 7 km when server is 30m above the ground and client is 2m above the ground with rubber duck antenna or inside a car
  • About 13 km when server is 30m above the ground and client is at some higher point ~40m above the ground with rubber duck antenna
  • About 17km maximum (non-reliable) between base and mobile station with antenna on the car roof
  • About 20km over the sea between base and handheld
• Signal levels
  • Successful decodes down to -19.75dB below the noise floor when using compressed APRS coordinates (smaller packets, about 50 bytes, 32 bytes without PATH, speed, altitude), see APRSDroid discussions on compressed corrdinates support and custom branches
    • https://github.com/ge0rg/aprsdroid/pull/159
    • https://github.com/ge0rg/aprsdroid/issues/170
    • https://github.com/sh123/aprsdroid/tree/aprsdroid_compressed
    • https://github.com/sh123/aprsdroid/tree/aprsdroid_compressed_gradle
• Polarization
  • Using horizontal polarization improves successful decoding probability and receiving range
• Interference
  • ⚠ Monitor your planned frequency, such as 433.775 MHz for ISM device activity, if there is strong interference from other users tune up or down it to minimize interference, it might be critical for long range
• Weather
  • Rain and high humidity levels decrease signal level by about ~3-6 dB on 433 MHz, could be higher on 868 MHz
• It might be useful to add additional pass band filter or broadcast FM radio reject filter, it seem to improve sensitivity when using external base antenna