Guido-
1TUNE THE "RUBBER" ANTENNA AT 433 MHz.
The original antenna is tuned around 470 MHz and therefore it ha a return loss of around -3dB at 433MHz. To tune it, you have 2 options. Without or With a Vector Network Analyzer.
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2Carefully remove the rubber cover
Hold the SMA connector with a clamp and gently move the rubber cover until it gets away.
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3Stretch the metallic (mine is made of copper) spring to obtain a total length of 17 cm, including the SMA connector
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4Refine the tuning to obtain the minimum return loss at 433 MHz.
Stretch a little (to decrease the frequency o cut the wire no more than 3 mm each time, to obtain the desired return loss (yellow line).
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LoRa APRS 433 MHz battery powered beacon
It has a WiFi Access Point for easy real time configuration. It sends: ham callsign, GPS or fixed coordinates, altitude, Volts and mA
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Hello Joe, you're perfectly right! In fact the return loss definition is: RL = 10 Log (Pi / Pr) and therefore it must be maximized. However the instrument shows the S11 parameter (S11 = - RL) amd for this reason the instrument result (S11) must be minimized.
A complete description for this ambiguity is here: https://en.wikipedia.org/wiki/Return_loss (see "Return Loss is a misnomer" and the chapter "Sign").
I really appreciated your suggestion.
Guido
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> ... obtain the minimum return loss at 433 MHz.
If you want the antenna to work well, tune for *maximum* return loss.
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