[Elecraft] Higher SWR When Using Amp.

[Jim Brown]

On 11/15/2010 3:43 AM, pastormg2 at verizon.net wrote:
> I have noticed when I fired up my amplifier on 40 meters that the SWR reading on the K3 when I tune up is higher then when I tune up on standby.
When a rig drives an amp, it does not "see" the antenna, it sees the 
input circuit of the power amp. When the amp is in bypass mode (that is, 
not in the OPERATE mode), your rig DOES see the antenna. What you are 
seeing  is some mismatch between the K3 and the power amp, which is the 
result of the input circuit of the power amp not being a perfect match 
to 50 ohms. This is QUITE NORMAL for most power amps. You should only 
worry about this if that SWR is much more than about 2:1. Most rigs, 
including the K3, will "fold back" (reduce power) to protect themselves 
if the SWR gets too high.

As long as the K3 provides enough power to drive the amp to the desired 
output level, don't worry about it.  With some amps, you can engage the 
K3's antenna tuner and tune it to provide a better match. That depends a 
bit on how the amp is being keyed.  It is also common for the mismatch 
to vary from one band to another, and from one place on the band to 
another.  In most power amps, the input circuit includes some form of 
bandpass filter.

73, Jim Brown K9YC