Hello Fergus!
The typical transponder operating frequency is 1030Mhz (if I remember
correctly). This means a very large loss through the typical RG58 cable over
14 feet. (the higher the frequency, the higher the loss) Ideally the x-pndr
antenna should be mounted away from other reflective surfaces, that means
getting it above the engine or propeller face lines. (more distance/length
needed in the Europa installation) I used RG-233/U specified at 14.5 db loss
per 100 feet. Of course, make sure whatever you use it is 50 ohm impedance!
The antenna may be optimal but if there is a large loss of signal
strength/energy getting to it then that transponder system is compromised.
Hope this helps!
kp
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