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Author Topic: Elecraft KPA-500 video overview...  (Read 11583 times)
W8JI
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« Reply #15 on: December 10, 2011, 08:35:38 PM »

The FCC 50 watts minimum drive requirement is for amplifiers out putting 1500 watts. The actual requirement from the FCC is the amplifier gain is limited to 15 dB or less. Most of the K3 users are into CW so IMD is not as important to them as the audio crowd.

I see the rule has changed. I wonder when they changed it?
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K6AER
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Posts: 5726




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« Reply #16 on: December 10, 2011, 10:07:39 PM »

Tom,

I only became aware of it about two years ago when I was hired to do the FCC certification for the 9500. Some engineers at Sprint noticed lots of changes in Cell Phone regulations first quarter of 2009.

Mike
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ZENKI
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« Reply #17 on: December 11, 2011, 04:12:56 AM »

What RF devices are used in the KPA500? I cant find that information on their web page.

I wonder if the KPA500 could be put into class A and be used with a K3 for better IMD performance? 100 watts to 150 watts should be possible if the power supply  and cooling  can handle the load.

I found time to run a few 2 tone IMD tests with my K3 and KPA500 combination today, these were on 80m using a 50 Ohm Cantenna load with the spectrum measurements taken with a Microtelecom Perseus SDR. The SDR receiver was coupled via a loop of wire around the coax to the Cantenna. The two tones used in the test are from the internal 2 tone generator in the K3.

First the K3 running at 20 Watts, the approximate power level used to drive the KPA500 to 400 Watts output:
http://www.astromag.co.uk/images/K3_2tone_20W.jpg

Secondly the K3/KPA500 running 400 Watts:
http://www.astromag.co.uk/images/KPA500_2tone_400W.jpg

Thirdly, the K3 running 100 Watts output with a spoken "four" into the microphone:
http://www.astromag.co.uk/images/K3_voice_100W.jpg

Finally, the K3/KPA500 running 400 Watts with a "four" as above:
http://www.astromag.co.uk/images/KPA500_voice_400W.jpg

73 Dave
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N4FBW
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Posts: 34




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« Reply #18 on: December 11, 2011, 03:56:02 PM »


The KPA500 uses a pair of MicroSemi VRF2933's RF Power MOSFETs

Datasheet on this device: www2.microsemi.com/datasheets/vrf2933_a.pdf

Quote
What RF devices are used in the KPA500? I cant find that information on their web page.
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G4AON
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Posts: 1407




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« Reply #19 on: December 12, 2011, 02:09:03 AM »

Quote
I wonder if the KPA500 could be put into class A and be used with a K3 for better IMD performance?

The KPA500 is quite clean, when fed from a clean source it can produce IMD products of -35 dB for 3rd order and little to see beyond +/- 8 KHz. The K3 at 20 Watts output (the typical drive level for the KPA500) spreads quite wide at lower level IMD products, but in fact when the combination of the K3 and KPA500 are looked at together they are no worse, and in some cases better than, many other QRO transceivers or transceivers/linears. Check the ARRL reviews for plenty of examples.

Running a KPA500 in class A would be pointless as the transceiver driving it contributes much of the IMD, also in class A a lot of heat would be generated. The K3 when running from the low power PA (the one used for powers up to 12 Watts or so) is no cleaner than the 100 Watt PA... there is no advantage in running a K3 at QRP levels to feed a class A amplifier.

73 Dave
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