[Amps] LDMOS availability

Jim Garland 4cx250b at miamioh.edu
Sat Jun 10 00:02:53 EDT 2017


There are two issues, here, one being the definition of Class C, and the 
other being linearity. I'm inclined to agree with Bill on both. It's not 
hard to imagine modulating the bias, so that on voice peaks, for 
example, the amp moves in the direction of Class B, but regresses to 
Class C at low drive levels.In that case, the class of operation varies 
with the drive. That said, Class C is by definition non-and that occurs 
whenever the device doesn't conduct over a full RF cycle.

I have a homebrew amp with two-tiered bias. On SSB, in pauses in speech, 
the amp is biased at a very low resting current (approaching Class C) to 
cut down on heat, but on voice peaks where the linearity is needed, it 
switches to Class B. One has to be careful playing that trick, however, 
to avoid switching transients.

73,

Jim W8ZR


On 6/9/2017 8:59 PM, Bill Turner wrote:
> ------------ ORIGINAL MESSAGE ------------(may be snipped)
>
> On Fri, 9 Jun 2017 20:56:33 -0400, Mark wrote:
>
>> But the bottom line is simply that if the device conducts less than 180
>> degrees it is class C.  If any method at all can be used to increase
>> linearity this does not change the class of amplifier, it just improves the
>> linearity.
> REPLY:
>
> Nonsense.  If the amp conducts less than 180 degrees it can not
> possibly be linear because the output in NOT a replica of the input.
> That's the definition of "linear".
>
> If you "modulate" the bias to make it linear, it is no longer Class C.
>
> Don't try to make things more difficult than they are. What you were
> taught years ago was and is correct.
>
> 73, Bill W6WRT
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps



More information about the Amps mailing list