E&I's Locked-On series of switchable impedance transformers provides the ability to simply switch from 50 ohms to multiple taps, to drive higher or lower impedances. The top range models provide a read back to easily verify that you have "locked-on" to the correct match and allow you to do this while delivering RF power.
Please refer to the information below:

HI-Z Impedances: 50, 100, 200, 400, 800 LO-Z Impedances: 100, 50, 25, 12, 6

The JT series Step up / Step down transformers offer low cost, flexible solutions to impedance matching. The JT series transformers operate over a wide frequency band and allow you to increase peak to peak voltage without having to increase the power of your RF amplifier. Due to their compact size, they can easily by placed in close proximity to the load and therefore minimize any losses due to the Q of your network.

• Impedance Transformation options from 3 to 200 ohms
• High Power Options Available
• Frequency Coverage from 10 KHz – 10 MHz
• Compact Designs