[hpsdr] Impedance Bridge error

[FRANCIS CARCIA]

Hi All,I need to measure the output impedance of my amplifier drain circuits to determine if compensation will improve efficiency on 6 meters where my drain efficiency could be a bit better. I also need to build and test a 4:1 combiner after that. It looks like Hermes in VNA mode will be perfect. I did the metal work for the bridge in a nice cast box and almost ready to make the PC board. I was looking at possible calibration errors between open and short calibrations and find if the two bridge resistors on the RF source side are increased in value the error decreases. This is due to the 50 ohm source impedance of the attenuation pad on the RF drive input. As the load changes between open and short the drive voltage changes. There is plenty of excess drive so why not increase the two resistor values to reduce the error. When these values are increased to 470 ohms each the error is greatly reduced. My question is will this introduce any other error? This voltage division would also reduce the need for high attenuation on the RX port to avoid overload.  Any thoughts?Frank WA1GFZ
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/attachments/20150518/2da9c831/attachment-0001.htm>