I'm putting an MRX into the panel of my RV-9A project. I would like it to attach to an external transponder type antenna. I've seen a VERY expensive cable available for doing this. I've been told that it's the price it is because it has an attenuator in it. Is there another way to attach the unit to an external antenna without using this high cost cable? Is an attenuator really required if the MRX is located several feet from the aircraft's transponder antenna?

Thanks

Kelly Johnson

The purpose of the attenuator is to match the MRX to a transponder antenna. To keep the cost of MRX down, we match the unit to the stub antenna, which has obviously different properties than a blade or stick-and-ball transponder antenna. The attenuator is custom designed to ensure the accuracy of the MRX when installed. Also, the cable is produced to your length specifications and matched to the MRX and attenuator. I hope this helps answer your question.

Is there a less expensive method to match the impedance of the MRX with a blade antenna? A better question is what is the impedance of the stub antenna? What is the impedance of the coax you are using? I would like an outside antenna as well to get a more accurate signal, but not at the cost of the coax and match-box.
Thanks-Dave

According to the manual, the antenna impedance is 50 Ohms. If 50 Ohm coax is used, and a 50 Ohm blade antenna, shouldn't the antenna swr be withing tolerance, provided the feedline is not too long/excessive?