[Elecraft] Question K3 ALC w/SPE Expert 1.3K-FA amp

[Joe Subich, W4TV]

Oliver,

> We now have devices capable of 22 or even 30 dB of clean
> amplification. Why should we not use it?

Many of the solid state devices that claim 22 dB or more of gain are
*not* clean at maximum output.  That 22 dB specification is based on
saturated power output - often in *pulse* service.  If the manufacturer
actually bothers to provide full gain and IMD curves for the device you
will quite often see the gain drops significantly at maximum drive and
or maximum output power while the "sweet spot" for IMD is 2 to 3 dB
*BELOW* rated (maximum) output for the devices in use.

Using 3 dB of negative feedback, another 3 dB of fixed input padding
and another 1 + 2 dB of switchable input attenuation to provide "ALC"
in the event of overdrive uses the total gain of the devices in a much
more intelligent way.  The high degree of negative feedback and fixed
input padding cause the exciter to see a very constant and resistive
load permitting the exciter to operate at its cleanest.  The negative
feedback also greatly improves IMD generation/linearity in the devices
and by keeping the devices typically below the 1 dB compression point
further minimizes IMD.

100 W to 1500 W (US Legal limit) is only 11.7 dB ... 100 W to 2500 W
(VE legal limit) is only 14.9 dB.  The US type acceptance standard
provides "overhead" in either case (if the amplifier is capable of
2500 W).  I see no reason - unless one *wants* to generate the typical
"dirty Italian" signal that one *needs* 22 or 30 dB of gain.  Most
QRP rigs are so dirty (worse in many cases than an IC-706) I would not
want to see them driving a 1500 W amplifier in any case.

73,

   ... Joe, W4TV


On 2015-04-03 6:01 PM, Oliver Dröse wrote:
>  > On a deeper level, to design an amplifier with that much gain is bad
> design
>
> Huh? Why is that, Joe? We now have devices capable of 22 or even 30 dB
> of clean amplification. Why should we not use it? Just because FCC does
> not allow it in the U.S.? I'm not bound to FCC rules and I'd rather
> prefer to drive such an amp with 1 or 3 watts from the KX3 to get 1 kW
> out than to cascade the transceiver with a driver amp and then a final
> amp. Of course I'm just bound to German law which does not contain any
> "stupid" (pardon me, but it is!) amplification limits, just the maximum
> allowed power. How we generate it is up to us radio amateurs overhere.
> That also means responsibility, of course. :-)
>
> Happy Easter!
>
> Vy 73, Olli - DH8BQA
> http://www.dh8bqa.de
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to lists at subich.com
>