[Elecraft] KPA500 Coax size requirements

Tue Aug 20 17:09:48 EDT 2019

I am pretty sure this dates back (literally years) to when the KAT500 first came out.
There was an issue if the KAT500 was not powered up before the K3, the K3 had problems during power on.
If the KAT500 was on a separate power supply many powered on the KAT500 before powering on the K3.
It was later discovered that the KAT500 only needed power to the coax power connector on the rear of the KAT500. The KAT500 did not actually need to be powered on. To this end it was advised that the K3 and KAT500 be powered from the same power supply.
All this went away in a K3 firmware update (version 4.9x. I don't remember which one) and has not been a problem since.
Since then the K3 and KAT500 can be powered from separate power supplies and the power supply connected to the KAT500 does not need to be on prior to powering on the K3. 

73,
Mark, WB9CIF

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of hawley, charles j jr
Sent: Tuesday, August 20, 2019 20:45
To: Ken K6MR <k6mr at outlook.com>
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA500 Coax size requirements

I think the issue is to be sure the tuner powers up with or after the K3.
But, mine turns on first and then the K3 later with no issues. I have pretuned it and run it on manual if that makes any difference.

Chuck Jack Hawley
KE9UW

Sent from my iPhone, cjack 

> On Aug 20, 2019, at 3:27 PM, Ken K6MR <k6mr at outlook.com> wrote:
> 
> “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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