regarding external ALC

[wayne burdick]

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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[Craig-89]

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 <[hidden email]> 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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>
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