[Elecraft] Small QRP antenna

Jim Brown jim at audiosystemsgroup.com
Thu Dec 29 23:41:22 EST 2016


On Thu,12/29/2016 3:07 PM, Bill Johnson wrote:
> Having "only" 5 watts doesn't change the need for proper termination and
> antenna match.

By proper termination, I think you're thinking about SWR and a match to 
the transmitter. This thread is several days and 20+ posts old, but I 
think I remember that the intent of the original poster was for portable 
operation. But I could be wrong. :)

There are two reasons for low SWR and "matching." One is to get the 
transmitter to provide power to the transmission line. If the mismatch 
is too high, the transmitter will "fold back" (reduce its drive to 
reduce its output power) to protect itself. Providing that match is the 
function of an "antenna tuner."

The second reason is to reduce loss in the line due to a mismatch. The 
SWR in a transmission line is determined entirely by the match between 
the antenna and the line. It is NOTHING to do with the match between the 
transmitter and the line.  In typical QRP portable setups, transmission 
lines are rarely long enough for loss to matter, so the match between 
the antenna and the line usually doesn't matter. And the antenna tuner 
takes care of match at the transmitter so that the output stage can 
supply its full power.

73, Jim K9YC




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