Q: The first character in my transmitted message is corrupted. After keying the transmitter module do I need to pause before I input my data and if so, for how long?

A synthesised radio transmitter module like the Wood & Douglas ST500 requires a certain amount of time to reach its specified operating levels. This is mainly due to the high frequency oscillator which needs to stabilise at its programmed frequency.


As a general rule of thumb, the RF stages in a transmitter would be expected to be within specified limits 50ms after TX-on is enabled. You should therefore hold off inputting data to the radio modules until 50ms after transmitter key-up. Ignoring this will mean that the first bits of the first byte of your message will not be heard by the receiving equipment.


It is good engineering practice to pause a short while after the last character is transmitted as well. 10ms is a commonly used value for this TX-hold on function.


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