# Repairing an immunity testing power amplifier

Repairing an immunity testing power amplifier.

From my workplace I got this old, decommissioned power amplifier which was used for immunity compliance testing before. It was made by Amplifier Research, the model is 10W1000B. According to the datasheet, at maximum setting and in the supported frequency range of 500 kHz to 1 GHz it’s gain is at least 40 dB with an output power of at least 10 W.

Since I want to extend my precompliance testing capabilities, I’m happy I got this amp. Together with my Rohde&Schwarz SMIQ03B signal generator, I finally can do immunity tests on my own projects by injecting HF into them.

Unfortuanately, the gain potentiometer shaft broke off during transport. Thats also the reason for the decommissioning… Easy fix for me! I quickly found a suitable substitute with the same value and mechanical dimensions. The replacement was a bit tricky because of the short wires and the coax shield that was soldered directly to the pot housing.

Finally, I tested, if the amplifier still meets it’s specifications. Together with 50 dB of attenuation I connected it to my network analyser.

With the potentiometer set to it’s maximum value, the gain is above 40 dB, reaching up to 43 dB. Therefore with the tracking generator set to 0 dBm, the power output also was above the specified level of 10 W.

I played around with the gain and figured out that 20 dB is the lowest value I can set to still achieve a flat response. At the minimum setting, the gain at 500 kHz is -7 dB and at 1 GHz 27 dB. Pictures will follow.