Ah, now I remember, thats what I was told as well.

Only reason why its earthed at both ends is because the rx Areial is connected through a SMB connector to a coax cable to bring it out of the metal box and hence the box is earthed through this connector. The coax then winds its way past the removable link and all the power wires through the middle of a moving sprocket into the arm. To create a 1/4 wave Dipole Areial the earth must be connected to a ground plate (chasis) at the point where the Areial leaves the coax cable. It would have been better if the ground plane was not already earth but connecting the areial to the rx with 50ohm coax to this areial gives approx (If I remember my areial theory) 50ohm also giving the best matching without additional components. The problem comes from not knowing the impedance of the Rx which is probably not 50ohms so there is a mismatch there with could casue problems.

The Rx after all is designed for a single wire areial. There are many possibilities and basically I used the old EMC trick, guessed, and it worked for us.