cd wrote:
> If you have a transceiver with a 3rd transmitter IMD -25db below pep,
> and
> the amplifiers third order imd is -40db, what is the final 3rd imd
> figure
> for the combined transceiver and linear?
>
> Secondly in the case ab2 grounded grid, when the driver contributes to
> feed
> through power what is the final figure when the driver has a poorer
> IMD.
> Also what happens with AB1 amplifiers? I ask these questions in
> trying to
> optimise the driver/final to obtain the highest 3rd order IMD.
>
> Craig
To calculate exactly this, you would need to know the phase
relationships of the intermodulation products, as the two 3rd order
products will combine as a vector, not a scalar. In principle, a poor TX
and a poor amp could be made to have minimal 3rd order products, by
carefully adjusting the phase shift between the driver and TX. Doing
this in practice would be another thing altogether, and even if you did
it for the 3rd order product, the 5th order would almost certainly need
a different phase shift.
In your case, the transmitter is much worst, so the overall amplifer
linear combination will be about 25 dB below PEP. If you can inprove the
transmitters IMD by using ALC to reduce the power, you should be inprove
on that a bit.
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