[Elecraft] KPA500 Coax size requirements

[Bob McGraw K4TAX]

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
>
>