[Elecraft] Re: QRP Dummy Load

[Don Brown]

Hi

Ahh Yes all true but the reason for the accuracy of the dummy load is =
because when setting up the SWR directional coupler in the KAT2, KAT100 =
or KPA100 you are using the dummy load as a standard to adjust the =
balance and power settings. For typical dummy load on the radio the =
value is not that critical but to get the settings right in the above =
the closer to 50 ohms the better. I use a slightly different way to set =
up the directional coupler than the manual. I have three loads with =
25,50 and 100 ohms. I set the balance per the manual and then set the =
power setting per the manual with the forward pot. I then set the =
reverse pot so the reading is 2:1 with the 100 ohm and 25 ohm. adjusting =
the balance slightly to get the same reading on both the 25 and 100 ohm =
then adjust the reverse to make it read 2:1. Then I connect a 150 ohm =
and see that it reads close to 3:1. This method seems to work better =
than just setting the reverse 20% higher than the forward pot as =
outlined in the manual.

Don Brown
KD5NDB


  ----- Original Message -----=20
  From: Alfred Lorona=20
  To: elecraft@mailman.qth.net=20
  Sent: Wednesday, August 06, 2003 7:19 PM
  Subject: Re: [Elecraft] Re: QRP Dummy Load


  Dummy load resistance accuracy and reactance problems need not be of =
undue
  concern for the following reasons. Accuracy better than plus minus 5
  percent, say, is seldom warranted. That kind of accuracy is not =
achieved by
  the most expensive meters available. But more importantly, ALL swr
  directional coupler type circuits decrease in accuracy as the swr =
approaches
  the magical 1 to 1 ratio. So what would you gain with greater load =
accuracy?

  In addition, the load can be of ANY value if you use the built in or =
an
  external antenna tuner. Adjust the tuner to the load and the =
transmitter
  sees 50 ohms. Try a 10 watt christmas tree incandescent light bulb =
with a
  tuner. Load impedance at the 10 watt level is about 1440 ohms with =
some
  reactance. But the transmitter dumps 10 watts into 50 ohms. :-)

  Ciao, AL


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