[Lowfer] Wm Beacon "Current" Question

[Mitch Powell]

Mike:
This may be a repeat of an earlier email - but I have had great results
using the rf ammeters I have built - for various power ( current ) levels
as shown on John's website, RFAmmeters for LF.  They are very simple to
build - calibrate very easily and never seem to change. The link is:
http://www.w1tag.com/RFA.htm/

Also - first copy of WM this Saturday morning... attached.
73
Mitch


On Thu, Nov 27, 2014 at 12:18 PM, JD <listread at lwca.org> wrote:

> Mike, keep in mind that a current meter for a loop is designed to measure
> higher current levels because an electrically small loop offers a very low
> resistance if constructed carefully.  A short vertical has inherently high
> capacitive reactance, which you neutralize with the loading coil, plus
> resistive losses in that coil, the ground system, and nearby environmental
> factors.
>
> Thus, from the P= I^2 * R relationship, we see that for the same power
> level, current in a high impedance circuit must be lower than it would be
> in
> a low impedance circuit.  That's why the meter deisgned for the loop barely
> responds in the case of the vertical.
>
> LowFER vertical antennas vary widely in their resistive component due to
> local soil conductivity and coil construction variations.  Most reports
> I've
> seen on successful beacons indicate measured RF currents typically in the
> range of 120-250 mA.  It's hard to get loss factors low enough to exceed
> 250
> mA for 1 watt.  Much lower than 120 mA, and the beacon may not get out very
> well...although nowadays with slow modes like QRSS, that's less of a
> problem
> than it would have been 15 years ago.
>
> John
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