[Elecraft] KXPA100 Hi PA current ?

[Don Wilhelm]

Glenn,

That voltage is very good, so rule that out.

There seems to be a lot of confusion in the ham community when dealing 
with RF in the Shack - a very common response is "my equipment is well 
grounded"  That grounding may be fine for AC mains grounding, static 
grounding, and perhaps even some help with lightning protection,  BUT it 
usually does nothing for the RF in the shack problem.  The wire to earth 
has some length and that length is part of the reason it does not work.  
Think of an 8 foot connection to the ground point - the connection point 
to earth is at a low impedance, but at the shack end it is quite a high 
impedance at 28 MHz because it is 1/4 wave long - that wire acts like a 
transmission line or as an antenna element to any RF that may be on 
shack equipment.  It will have some impedance to ground at any frequency 
- I just use 8 feet and 28 MHz as a convenient example.
About the only way to eliminate RF in the shack is to keep it off the 
feedline shield in the first place, and that means use of common mode 
current chokes.  The 'balun' at the antenna feedpoint may not be doing 
the job effectively, or if the feedline is not arranged perpendicular to 
the antenna for at least 1/4 wavelength, the feedline may couple with 
the radiator and actually pick up RF.
K9YC has provided information on effective common mode chokes in his "A 
Ham's Guide to RFI".  You may need to install such a choke not only at 
the antenna feedpoint, but also at the point where the feedline enters 
the shack.  I recommend that approach to anyone who uses an OCF antenna.

73,
Don W3FPR

On 6/1/2014 11:54 PM, WA7SPY wrote:
> Hi Don,
> Thank you for the information and input about OCF antennas. I did a measurement of the supply voltage to the KXPA100. here is what I Measure with my Fluke 77 meter:
>
> The voltage measurement was taken at the supply power plug from the amp that plugs into the KX3 to power it. I have the internal batteries installed in the KX3 so doing the test was easy. I am using an Alinco DM-330 MVP power supply with a very short cable run the the KXPA100. The supply voltage reads 15.1 volts without the amp or KX3 transmitting. With the power setting on the KX3 set to max 110 watts. When the KX3 is keyed and the amp is active I measure 14.6 volts. The voltage drop is not that big in my opinion.
>
> I have a 10 foot ground round sunk all the way down with a heavy braided cable less than a 6 foot run to a 1/4 inch thick brass 8x8 inch plate. I then have braided jumpers going to the KX3 and KXPA100 less than 8 inches from the brass plate to my equipment.
>
> What else should I do or look for? I have to say my Carolina Windom performs extremely well!
>
> Thank you,
> Glenn WA7SPY
>
> Glenn Maclean
>
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