[Elecraft] KPA500 Coax size requirements

[Jim Brown]

On 8/20/2019 3:49 PM, Nr4c wrote:
>  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?

The KPA500 runs on 120V or 240V.  The KAT500 runs on 11-15VDC. My two 
K3s (original model) run on a 100Ah Bionenne LiFePO4 battery, which 
stays above 13V for 90% of its charge capacity; the IMD (clicks, 
splatter) of a K3 increases with lower DC voltage, and lead acid 
batteries stay below 12V for most of their discharge curve.

The rest of the 12V gear in my shack, in addition shack lighting, runs 
on a 100Ah sealed lead acid battery. Both batteries are float-charged 
using Genasun charge regulators from spare Thinkpad power supplies. The 
Genasuns are MPPT chargers, so they step down the 20V from the power 
supplies to the battery voltage.

> 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.

Has nothing to do with the amp -- study the ARRL Handbook and Antenna 
Book to learn these fundamentals. As others have mentioned, the major 
reason for using bigger coax is reduced loss, whether mismatched or not.

Someone suggested open wire or two-wire line with a balun at the tuner. 
That can transmit OK, but unless you're lucky enough to live in the 
middle of nowhere, that's a recipe for lots of receive noise. You can't 
work what you can't hear. The quietest antennas are resonant and 
reasonably well matched to the coax that feeds them, and with a serious 
common mode choke at the feedpoint (that is, up in the air).  Lots of 
specific advice atk9yc.com/publish.htm. Look for the HF choke cookbook, 
the RFI tutorial, and how to chase receive noise.

73, Jim K9YC