[Elecraft] K3 and KX3 questions for Wayne

[Bill Frantz]

An addition to Jim's comments below.

All 100W rigs, regardless of manufacturer, whether the amp is 
part of the radio or a separate unit, develop significant 
distortion as the voltage drops. We noticed the effect at CQP 
last year. We were operating on batteries as our hosts have a no 
generator rule. As our batteries got lower, our 3 stations -- 2 
K3s and a KX3 with KXPA100 -- started interfering with each 
other. The problem went away when we replaced the batteries with 
fresh ones.

This distortion will also affect your signal as received by 
distant stations, so it is undesirable in a rig unless you want 
a reputation for a bad signal.

One way to be able to get maximum runtime from your batteries is 
to use a voltage booster regulator. I use a N8XJK Boost 
Regulator from TGE. This device boosts the battery voltage to 
the radio. Mine shows 13.9 volts, receive and 13.4 volts key 
down at 100W on 160M, even with relatively low batteries. (It 
does have a low voltage cut off to protect the batteries.)

The N8XJK Boost Regulator does generate some minor birdies on 
receive, so I have it set up to only boost voltage when it 
senses RF output from the transmitter.

73 Bill AE6JV

On 5/22/16 at 2:46 PM, jim at audiosystemsgroup.com (Jim Brown) wrote:

>On Sun,5/22/2016 11:46 AM, N6MQL wrote:
>>Although I appreciate all of your answers I specifically asked 
>>these questions of Wayne because I was making a point to let 
>>him know of my disapproval of the fact that the KXPA100 amp is 
>>incapable of running a full 100 watts on a standard 12v battery.
>
>Michael,
>
>A careful reading of the online data sheet for the KXPA100 is instructive here.
>
>http://www.elecraft.com/KXPA100/kxpa100.htm
>
>The first line says "100 watts at 13.8 V, 1.8 to 29.7 MHz and 
>80 watts 50-54 MHz PEP CW/SSB/DATA; ± 1 dB"
>
>Two points: First, the amplifier is rated for 13.8V, NOT 12V. 
>Second, the rating is +/1 dB, which is +/- 20% power. Thus, 80W 
>on the HF bands is within spec for 13.8V at the amplifier terminals.
>
>The second line says "13.8 VDC powered; 20 A typical current 
>drain (11 V with lower output. 15 V max)"
>
>This clearly means that the unit is designed and rated for 
>13.8VDC, can be operated from 11V to 15VDC, and will have 
>reduced output at lower supply voltages.
>
>Obviously, Ohm's Law dictates that resistance of the DC supply 
>conductors will reduce power supply voltage at the amplifier 
>terminals, so while we may have 12V or 13.8V at our battery 
>terminals, the voltage at the end of 6-12 ft of cable will be a 
>bit lower with a 20A load. For example, the drop in 6 ft of #10 
>is 0.24v; for #12, it's 0.38V, and for #14, it's 0.6V.
>
>As others have noted, the operating voltage in so-called 12V DC 
>power systems using lead-acid batteries is not 12V, but rather 
>13.8V. If you buy an AC power supply for ham gear, it will 
>likely leave the factory with its voltage regulator set for 
>13.8V. Open the manual or the spec sheet for nearly all ham 
>gear and you will find the supply voltage specified as 13.8VDC.

-------------------------------------------------------------------------
Bill Frantz        | Airline peanut bag: "Produced  | Periwinkle
(408)356-8506      | in a facility that processes   | 16345 
Englewood Ave
www.pwpconsult.com | peanuts and other nuts." - Duh | Los Gatos, 
CA 95032