In message <19980930.132904.14246.0.w6frmarv@juno.com>, marv gonsior
<w6frmarv@juno.com> writes
>Steve,
>
>The customary rule of thumb in the design of SSB equipment dictates that
>if the two amplifiers are of equal distortion level.......the resulting
>signal will be degraded by 3dB. If the final amp is 3dB better than the
>driver, the result will be about 1 dB poorer, etc. Finally, a figure of
>10dB will not cause any degradation of the driving signal. I have seen a
>table on this relationship but for the moment I can remember where it
>was. It could have been in one of the Collins books.
>
>Marv, W6FR
>
As G8WRB mentioned earlier, the final result depends on the phase - the
IMD can cancel as well as add, so your rule of thumb might well be
'typical' as opposed to my 'worst case'. Things can also vary a lot
depending on the nature of the non-linearity producing the IMD. Some
ampifiers are nice and linear up to a clipping point when distortion
rises very suddenly, others have a banana shaped Po/Pin and have fairly
constant IMD as Po varies. If you've got one of each in a chain it can
be very wierd.
It's funny, whenever I make the measurements, I seem to get worst case
results :-)
Steve G8GSQ
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|