In message <000501bdd580$7a8f8c40$59b56ccb@computer>, craig
<bearl@ozemail.com.au> writes
>
>Has anybody built or played with high IMD solid state amplifiers? There is a
>system called " Feedforward" which is well explained in "Single Sideband
>Systems & Circuits" But i would like to know if anybody has implemented a
>working model. Third order imd figures of greater than 60dbc is achieved. It
>certainly would make a great driver.
>
>Alternatively could your achieve high level of imd performance of greater
>than 60db by using say a 4cx600J, with low plate voltage and low drive power
>to achieve good third order imd performance? Maybe there is a high
>performance imd tube that i am not aware of. Certainly the vast majority of
>ham transceivers the imd performance is certainly very poor. Anybody looked
>at the FT847? its a SHOCKER, maybe i just have bad example.
>
>Craig
Joining late here...
Notwithstanding comments about which sorts and which levels of IMD
'really' matter, I reckon the only realistic way of getting super clean
signals in amateur circumstances is to go class A. Lots of heat, low
efficiency. Very simple.
As an example, my 2m tvtr runs a 70W class AB 28V device in class A at
28V, 2.5A. At the intended output level of 25W pep, on a 2 tone test 3rd
order IMD is -45dBc, I can't measure anything else.
Don't try to do this by winding up the bias on a class Ab circuit. You
need to use an active bias system which forces the current to be
constant.
Steve G8GSQ
>
>Craig
>
>
>--
>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
>
--
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
|