[Elecraft] Amplifier thoughts

[Jim Brown]

On Wed,3/29/2017 11:47 AM, Ron D'Eau Claire wrote:
> An SWR approaching 10:1 means high RF voltages on a coaxial line at the voltage loops

Remember that the SWR on a transmission line, and thus the loss in the 
line, is determined ENTIRELY by the match between the antenna and the 
line, NOT between the line and the transmitter.

The SWR measured at the transmitter is a measure of the difference 
between the impedance the transmitter WANTS to drive and the impedance 
of the load connected to it. If that INDICATED SWR is high, a solid 
state transmitter will "throttle itself back" to protect itself, but 
that's not LOSS. The function of an antenna tuner is to make the 
transmitter happy by giving it a load that it's designed for, so that it 
can put out its full power.

For example, a long wire antenna of random length might be nowhere near 
50 ohms resistive, so must be transformed to 50 ohms resistive so that 
the transmitter can put power into it. Likewise, an antenna perfectly 
matched to 75 ohm coax or 150 ohm twin lead has no excess loss in the 
line but needs a matching network to make the transmitter happy.  My 
high dipoles (at 100 - 140 ft) are fed with 75 ohm coax to minimize the 
loss in the line.

73, Jim K9YC