On 7/3/2016 10:05 AM, Steve Hunt wrote:
Rudy,
http://www.karinya.net/g3txq/temp/52_mix.png
It achieves Rs>5000 Ohms from 10Mhz thru 28MHz, and Rs>8000 Ohms from
12MHz thru 21MHz.
Steve G3TXQ
It is more useful to think about Rp than Rs. Rp determines the
power dissipation for a given voltage. Although Z is a figure
of merit for how well the antenna works, Rp is a figure of merit
for how much power can be handled. On the G3TXQ curves, note
that where Z=Rs, it is also true that Z=Rp. Away from that
frequency, the general trend is that Rp monotonically increases
with frequency, at least up to resonance.
For the RF amplifier DC feed, Rp is everything. Getting a high
enough Z pretty much takes care of itself if Rp is sufficient.
In the amplifier, you not only need to minimize the amount of
heat, but also the thermal resistance for cooling purposes.
It is a very complicated problem and there is no universal
solution. Unlike the antenna case, there is no requirement
that Z is mostly resistive. It is actually better if it
is mostly reactive.
It's nice to brag about extremely high Z values, but even if
Z=infinity, all you have accomplished is that you have
disconnected the feedline from the antenna. It doesn't
guarantee there will be no feedline currents. Also, it merely
PERMITS the antenna to be balanced, if there is no external
conductor otherwise perturbing it. It does not guarantee
balance.
Rick N6RK
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