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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
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