AM/FM Antenna Upgrade

Now with the more acceptable exhaust note (the twice pipes were too loud!), I can finally enjoy listening to the radio.  I've struggled with what type of antenna to replace the broken original with.  I first tried an 11" rubber ducky that didn't work very well, as well as a hidden antenna that mounted to the window; again not working too well.  I decided it was time to investigate how to repair or replace the old semi-automatic antenna that Datsun included originally.

The great feature of the Datsun antenna is that it is controlled by the radio head unit with a switch, allowing the driver (or passenger) the ability to raise or lower the antenna to the proper level to tune in stations.  (notice the switch on the upper right)

Unfortunately my car arrived with the antenna broken off.  Modern antennas are fully automatic meaning that they go up when powered up and down when the power turns off.  I needed to find a semi-automatic that I could modify to work with the Datsun radio.  Below is the original antenna (left) and the new one I was able to source (right).  Notice the original Datsun antenna had a modulator box already installed that allowed the switch to power one wire for up, the other for down, and use the body of the antenna for a ground; this is how the switch works too.  The modern semi-automatic that I sourced just reverses the polarity to have it go up and down.

I was able to find a diagram of a door lock actuator that would allow me to use the original Datsun radio switch and wiring while making the new antenna work by means of two relays.  Essentially reversing the polarity of the output wires.  Thanks to the original designer of this diagram, it came in very handy!!  Just need to make sure you get 5-pin (5 pole) Bosch style relays.

Below is my work in progress and then the final cleaned up version.  Two inputs, Two Outputs, and a Ground.

 

Mounting the antenna is fairly straightforward.  After mounting the top to the rear quarter panel I hooked up the wiring to make sure everything worked correct, followed by cleanly attaching the relay bracket that I fabricated and then the antenna mounting bar to ensure my quarter panel didn't move any more than it needed to when the antenna was up.

 

The results are great! I can accurately tune into any station in my '72 240z's radio that I can in a modern car with a digital tuner (meaning the antenna performs as good).

Below are links to the parts I used (not including the extra wire, connectors, and brackets I fabricated):

Semi-Automatic Antenna:
http://smile.amazon.com/MQ-1-Semi-Automatic-Power-Antenna/dp/B004675YOK/ref=sr_1_1?s=automotive&ie=UTF8&qid=1432508441&sr=1-1&keywords=Semi+automatic+antenna

Bosch Relays: 
http://smile.amazon.com/Relay-Harness-Bosch-Style-40AMP-HRNS/dp/B005HFYE1O/ref=sr_1_2?s=automotive&ie=UTF8&qid=1432508382&sr=1-2&keywords=5+Pin+Relay