>In any properly designed receiver, the IMD performance of the RF amp will be
>a relatively small contribution. The mixer, and occasionally, high frequency
>crystal filters are the major causes of IMD. Switching off the RF amp
>reduces signal levels into the mixer, and thus mixer IMD. Getting the
>performance in an RF amp is relatively easy, especially if you use noiseless
>feedback and a good linear transistor running well in Class A with plenty of
>current.
I stand corrected. And now that I think about it, I don't know why I
rushed to agree with Tom. If the IM distortion was caused just be the
preamps in rigs like the FT-1000D and mixers are hard to overdrive, then
I would expect my FT-840 to have better receiver IM performance (no
preamp). It doesn't. And also if mixers can't be over-driven easily (as
Tom suggests) then why do they include additional fron end attenuation
levels on rigs like the FT-1000D?
Shame on me, I should have thought my post through more thoroughly before
responding!
73,
Jon
KE9NA
--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
--
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
|