I have an ELT question.
On 121.5 if you crash, drop it or flick the switch or indeed if it activates itself due to a fault, the signal is instant.
What about on 406? It transmits data. Is that instant on activation also?
The difference between the 121.5 and 406.25 MHz is
1. when the search satellite passes over the ELT the 121.5 info couldn't be saved and would be transmitted down immediately, in case no LUT(local user terminal) was within the footprint of the satellite the information would be lost. 406.25 can be saved till a LUT comes within the satellite footprint.
2. The position is judged by the doppler shift generated by the satellite moving over the ELT. Accuracy of 121.5 is lower (said to be about 20 Sq miles) than 406.25 which has a higher frequency so the accuracy is higher ( said to be about 5 Sq miles)
3. the transmission contains a unique code which is part of an international database. the Tx contains this code and enables the identification of this tx source.
4. transmission time for all frequency is same, ie there is no delay in any frequency.