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GM7HUD > TECH 08.11.08 12:18l 20 Lines 887 Bytes #999 (0) @ WW
BID : 405266GM7HUD
Read: GUEST
Subj: Re: Coded Orthogonal Freq Div Mux
Path: IZ3LSV<IK2XDE<DB0RES<DK0WUE<7M3TJZ<ZL2BAU<GB7ESX
Sent: 081108/0832z 26314@GB7ESX.#31.GBR.EU $:405266GM7HUD [Witham, Esx]NNA V3.1
G8MNY wrote:-
>
> PA EFFICIENCY
> It should be clear that amplifying all the carriers in 1 PA is not wise way of
> going about multiple carrier transmission. Ideally each carrier could have a
> linear PA (needed for QPSK) & a loss free RF directional coupler/adder used.
> But the short term cost of this complexity is excessive, & the system
> flexibility (no of carriers) will be hardware fixed.
In reality EER is used with non-linear amplifiers for real QRO solutions.
In addition the I and Q components can be low level amplified to clipping
and then filtered before that signal is passed to the linear PA stages.
This can gain an extra 2dB in performance. Filtering the components before
the main PA will results in a higher BER at the receiver due to in-band
self QRM but the coding used by the modulation scheme is normally robust
enough to cope with this.
73 de Andy GM7HUD
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