[Orry Verducci]

Didn’t realise QPSK, 8PSK was to do with signal strength, that’s interesting I’ll have to Google it.

It doesn't affect the signal strength, but rather the density of the signal which in turn affects reliability in marginal conditions.

It's a bit complicated to explain, but basically they're different variants of modulating the analogue signal to carry digital data. QPSK can carry two bits of data within a symbol, 8PSK can carry three, so 8PSK can carry more data in the same bandwidth. However it does so by allowing more variations in the signal phase.

If the signal is noisy it becomes harder for receivers to determine the phase of the signal, which can cause the signal to be misread as neighbouring values resulting in corrupted data. 8PSK has more variations closer together, so as the signal gets noisier (as is the case with satellite rain fade) it starts to be misread quicker than QPSK. Therefore if the 8PSK signal is unreliable switching to QPSK is a quick and easy way to increase the signal to noise ratio and restore solid reception, at the expense if reducing the data you can uplink (i.e. lower video birate required).

To put it in to layman's terms, it's the difference between listening to someone talk fast on a weak radio signal, or listening to someone talk slowly. Both are noisy and hard to understand, but you'll mostly make out what the person talking slowly is saying, whereas you'll get little of the person talking fast.