[Elecraft] [Elecraft-K3] K3S to be discontinued

[Joe Subich, W4TV]

On 2019-11-04 10:48 AM, Bill Johnson wrote:
> Seems most transmitters are in the same boat using solid state 
 > transmitters/amplifiers, vs. tubes.

The issue is that 12V transistors are simply not capable of providing
the "clean" voltage swings necessary to generate 100 - 120W peak power.

A typical transistor/FET has a series output impedance of around 1 - 1.5
Ohms.  Thus if the peak current is ~10A per device, the transistor is
operating from cut-off to saturated - with the unavoidable distortion
(clipping/saturation) at each end of that range.

Simply put, insistence on more than about 60 W PEP from a pair of 12V
devices is *asking for IMD* and "active predistortion" only masks that
issue with a significant cost in complexity and DSP hardware.

Equipment designers should give up on 12V devices for "base station"
radios and go to 48V devices - even at 200 W PEP output levels.  The
designers should stick to 60 W output for 12V devices.  That level is
more than enough to drive an amplifier in the  KPA-500 class to rated
output and close (if not sufficient) for even a KPA-1500 and can be
improved, if necessary, with much less complex precorrection systems.

Redesigned with bias levels and transformers optimized for the lower
power levels, perhaps with increased negative feedback, the K3/K3S
could exhibit *much* - at least 10 dB - better IMD at 50 - 60 W PEP
output (although efficiency would probably suffer for those who just
absolutely need to run the rig from a 12V battery pack on a picnic
table).

73,

    ... Joe, W4TV


On 2019-11-04 10:48 AM, Bill Johnson wrote:
> Thank you, Bob.  Rob, clarified to me.  Seems most transmitters are in the same boat using solid state transmitters/amplifiers, vs. tubes.
> 
> 73,
> Bill
> K9YEQ
> 
>