[Elecraft] regarding external ALC

[Ham]

Hi Wayne



" We're mindful of the negative
> impact ALC can have on 
> transmit signal purity, a subject of recent debate
> within testing 
> organizations."

Is it then safe to assume that the issue  of ALC
overshoot  and ALC induced wideband IMD  has been
addressed in the K3's design?  

I was also wondering about the transmit IMD
performance data of the K3/10. I can find no official
IMD data for the RD16HHF  MOSFET. Although i do
believe at low power outputs the IMD performance is
indeed good.  Have you made any  2 tone measurements
at various power level settings for the K3?


Craig
VK3HE


--- wayne burdick <n6kr at elecraft.com> wrote:

> Hi Enno,
> 
> Transmit power control via the ALC input (AUX I/O
> pin 15) is planned, 
> but not finalized. We're mindful of the negative
> impact ALC can have on 
> transmit signal purity, a subject of recent debate
> within testing 
> organizations.
> 
> External amplifiers vary widely in their loop gain,
> causing problems 
> with distortion. Many amplifiers, like the Alpha
> 87a, specifically say 
> not to use external ALC. A properly operating,
> internally ALC 
> controlled rig like the K3 does not need external
> ALC input to connect 
> to an external amp. In general, external ALC should
> -not- be used as a 
> way to control rig power.
> 
> As for the voltage range, this is not a typo: the
> ALC input handles 0 
> to +5 V. Once ALC is working to our satisfaction,
> we'll provide simple 
> interfacing information that will allow the use of
> negative control 
> voltages (probably a resistive divider pulled up to
> a positive supply, 
> or at most an op-amp circuit).
> 
> Meanwhile, the K3's DSP-based early-stage ALC is
> very effective at 
> preventing amplifier overdrive, and should suffice
> in nearly all cases.
> 
> 73,
> Wayne
> N6KR
> 
> > Scanning through the manual I saw that the ALC
> voltage to be applied 
> > on pin
> > 15 of the ACC connector needs to be in the 0 - +5V
> range. This worries 
> > me a
> > bit because many (if not virtually all) linear
> amps output a NEGATIVE 
> > ALC voltage for
> > feedback to the transceiver.
> >
> > Is the +5V maybe a typo (i.e. should it be -5V) ??
> >
> > -- Enno, PF5X
> 
> 
> ---
> 
> http://www.elecraft.com
> 
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