[Elecraft] KPA500 Coax size requirements

[Ken K6MR]

“The KAT500 can be {should be} powered from the radio 12V supply.”



Interested why this is true.  Can the KAT500 tell the difference between Elecraft 12V and Generic 12V?  Seems odd.



I ran two KAT500s on generic 12V from a DIN rail power supply for 5 years.  Necessary because the tuners and the amps were remoted in a closet 20 feet from the operating desk.  No problems.



Ken K6MR





________________________________
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> on behalf of Bob McGraw K4TAX <rmcgraw at blomand.net>
Sent: Tuesday, August 20, 2019 12:59:11 PM
To: elecraft at mailman.qth.net <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] KPA500 Coax size requirements

Carter:

The KAT500 can be {should be} powered from the radio 12V supply.   I
don't suggest a separate wall wart.

The KPA500 can be powered from either 120VAC or 240VAC, your choice.  It
should drive on all bands with 20 to 30 watts output from the K2 to
reach full 500 watts output from the amp.

As to coax, yes RG-8X is OK up to 30 MHz as long as the SWR is low.  The
Belden Power rating is 1000 watts up to 10 MHz, 370 watts at 50 MHz.
Loss is 0.9dB / 100 ft @ 10 MHz and 2.1 dB / 100 ft at 50 MHz.   These
power ratings are matched conditions.

What is the SWR on your wire loop on the feed line for all bands?   Per
Belden, the UL voltage rating is 300 V RMS.  Thus 500 watts at 50 ohms,
i.e. 1:1 SWR, is 158 volts.  However, 500 watts into 500 ohms, i.e. 10:1
SWR, is 500 volts.  So to answer your question, YES and NO, depending on
SWR on the coax between the tuner output and the loop antenna feed point.

In general, R-8X is OK at 500 watts below 30 MHz.   From experience, it
will get "warm" to the touch.  "Warm" is created by loss which is then
heat generated from RF.  And that is RF which is not getting to the
antenna.

Personally I'd opt for a balanced open wire feed to the loop and a very
good 1:1 balun rated for legal limit or more at the KAT500 tuner output.

73

Bob, K4TAX


On 8/20/2019 2:11 PM, Carter Craigie wrote:
> Hello friends,
>
> I am contemplating buying a KPA500 amplifier/tuner Combo, and driving it
> from my Elecraft K2/100 rig. I hope I would be able to do that!
>
>   From what I have read on eHam Reviews, it appears that I can run the
> amp/tuner combo on 117v. from the convenient wall socket. Is that correct,
> as well?
>
> I cannot find any mention of the coax requirements, from the radio/combo
> out to our 80-meter wire loop antenna. Right now, using only my K2/100 I am
> able to use  8X coax.
>
> Will I still be able to use that coax cable with up to 500 Watts output?
>
> What other considerations do I need to make?
>
> Thanks in advance,
>
> Carter Craigie, N3AO
> Blacksburg, VA
>
>

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