[Elecraft] High Accuracy Wattmeter

[DolfinDon@aol.com]

In a message dated 2/11/2002 6:37:37 PM Central Standard Time, W1CG@QSL.net 
writes:


 need a high accuracy wattmeter for reading power from 1 to 10 watts into 
a 50 ohm load with a precision of 0.05 watts or less over the entire 
scale. 

+++++++++++++++++++++++++++++++++++++++++

Hi

The only way I know of to do what you are asking is a RF thermistor mount and 
matching meter with a high power attenuator in front of that. The problem is 
you are requiring an accuracy of 0.5% at full scale and you are not going to 
find a watt meter with that accuracy that is cheap ($1K and up) You can make 
a meter that is fairly accurate at one frequency but its not easy to do 
across the bands. A thermistor mount converts the RF to heat and compares the 
rise to a standard thermistor in a bridge circuit. The meter converts the 
difference read in milliwatts. The power attenuator drops the power to a 
level the thermistor can handle. I have a setup like this and it is very 
accurate from DC to about 1GHz and slightly reduced accuracy to 18 GHz


Don Brown

KD5NDB

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