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Author Topic: FCC Invites Comments on Petition to Eliminate 15 dB Gain  (Read 40262 times)
KA4KOE
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« Reply #120 on: August 08, 2016, 06:06:18 AM »

The efficiency figures listed are opinions without hard data. The sample calculation, taken as it was presented, was correct. Unless you put an amp clamp on the power cord the figures are purely opinions. Good engineering practice also dictates that you don't excessively oversize as that leads to other issues. Any large well designed amplifier should have step-start anyway. Up-sizing a house service in this example is unnecessary.
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ZS5WC
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« Reply #121 on: August 11, 2016, 10:22:24 PM »

 :)Hi John,(KA4WJA)
Thanks for your reply and publishing the IMD figures of the 3 EXPERT amps.
It would seem the 1.3Kfa has VERY much worse (3rd order imd) at rated output.

I think using a single package (dual device) FET was optimistic, maybe the rated O/P should be around 1Kw.
I have spoken to several owners of the 1.3K-fa however, and they seem oblivious to any splatter issues.
I know these amps were recently used in DXpeditions, and no cross-band splatter was observed.

I recently had a report of splatter on my 1K-FA. Found the BIAS incorrectly set from factory , reset to 250mA per device, and splatter was gone. She is now super clean.

So maybe the Expert dealer in the USA could be contacted re the issue, I'm not sure if QST did a test on the 1.3K-fa?.
Maybe someone with the required test gear could confirm the 3rd order IMD?.

73 de William
ZS4L / ZS5WC
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ZENKI
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« Reply #122 on: August 19, 2016, 04:54:35 PM »

Elecraft should work harder at improving the IMD of their radios. While radios like the K3 do have a well behaved ALC, the IMD performance of the K3 is not that great, its poor.

Elecraft is however right. It would be nice to be buy a ultra clean 1 watt K3 and drive a 500 watt or 2kw amplifier with  the 1 watt driver radio. The military and most commercial HF  transmitters work this way. They have no ALC and  have a transmitter gain control. These military radios have exceptional IMD performance like 50db down at 5khz.

In a conversation with Elecraft at SeaPac on this topic, they seem anxious to see the limit lifted. Indicated that with very small changes on the input configuration the KPA-500 could be driven "cleanly" (their emphasis, I might add) by 10 watts with 500 out.  Just imagine a 500 watt KX2. :-)
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