Radio Antenna Preamp Analysis

About a week ago, through my stupidity while at a drive-through car wash, the antenna base on the 2007 was damaged. Fortunately, Steve Woodruff came through with a replacement from a salvage 2008 at an excellent price and promptly shipped it to me. Thanks, Steve!!

It was quite easy to replace the antenna base but I needed to visit my local dealer yesterday evening to purchase new plastic clips that retain the rear of the headliner. 2 out of 3 broke, they are quite delicate.

There actually is no need to remove hatch trim to do this, there is enough play to gently lower the headliner sufficiently to gain access to the antenna base.

Anyway, since I now had the broken antenna base, I thought it might be fun to analyze the preamp's capabilities.

I attached a couple of photos of the preamp circuit board. Looks like one transistor is the active element. A separate wire is used for the power supply.

My procedure was to use my HP 8640B signal generator as a signal source. I used a receiver with an S-meter to provide an indication of relative signal strength. I provided 12VDC to the power supply wire and the current draw was 15 mA.

Unfortunately I was not able to discern that the preamp contributed any amplification to FM signals. Further it appears that it diminishes AM signals, which I suppose is not surprising since the preamp has no way to band switch and the tuned circuits appear optimized for the FM band.

It is certainly possible that the preamp was damaged when the whip snapped off. In any event, I thought the group might be interested to see what the preamp board looks like.

 

Hi Pat,

Thanks for your comments. The HP 8640B has an N to BNC adapter. Then, a 2 ft. length of RG-58 coax with BNC connectors, to a female BNC to two small alligator clip jumpers, clipped to the little black wire sticking up (which connects to the antenna whip) and to the metal base for ground.