I had to replace a broken mast on the '97 XK8 I recently purchased. I bought one at Rockauto.com (URO part LNA4134AA), and installed, but the AM reception was poor ( I like to listen to Talk Radio). I purchased a second mast from Terrysjag, thinking it might be better since it referenced the Jag part number. Received the same aftermarket Mast, but thought I would try it anyway. It installed a bit tighter than the first mast, but I still have AM radio reception issues. I can stand in the garage and move the antenna ( like the wind hitting it), and the reception goes in/out ( like static, but it's actually cutting in /out).

I took the antenna out, and dismantled it. Checked all the grounds, and checked continuity between the antenna cable and the connection at the antenna. Everything checked out good. Put the antenna back together, and reinstalled and still have the issue. I can see there is a slight tolerance between the largest of the antenna sections ( last one to come up) and the sleeve that fits tightly inside the antenna. Moving the antenna back and forth you can see maybe .020" of movement. Seems to be enough to make/break the connection.

Looking for any other troubleshooting / repair ideas before I move towards an aftermarket replacement of some sort. Any help would be appreciated!

 

Darbysan, sorry but the AM part of the radio receiver doesn't use the antenna in the rear. Its for the FM band. You're likely dealing with 2 or 3 issues:

1) the radio manufacturer focuses on FM due to demand.

2) an internal ferrite rod antenna is internally installed for AM reception

3) your car is made of a grounded metal shell - hard to receive an AM signal through that. Guess that's where a convertible is better :-)

Got a small AM radio? Tune a strong favorite station.Take it inside the car. Does reception drop? Well I suppose this won't do much more than show you if the car's AM section is on par with the one in your hand, just thinking out loud. If not maybe there's a slight chance that a radio upgrade will help?

I've read of external AM antennas that appear to boost the signal in proximity to the radio. I'll leave that for you to research further. Google C.Crane AM radio, they do make radios and antennas. Just not sure if you could port that tech to your car.

I haven't listened to or messed around with AM in so long, I'm not sure what else to suggest. Just know your not going to really get anywhere working on the cars antenna - it might help marginally but its tuned for the wave length of the FM signal. Your AM tuner uses the ferrite rods built in.

John

 

The mast antenna in our cars functions for AM, as well as for FM. You can confirm this by unplugging it while tuned to an AM station (or, if you have installed a manual antenna override switch, by lowering the antenna). At AM frequencies, where the wavelength is quite long (about 300 meters), the antenna mast together with the skin of the car (which forms a ground plane) function as what's called a short monopole antenna. "Short" here means much less than the signal wavelength.

The material, the thickness, the length of the antenna mast do not matter much. Most important are good connections to the mast and to the car's skin (ground). I think Darbysan's problem is likely a poor connection somewhere.

 

Now I would have thought you're hearing the loss of ground with the antenna unplug. Guess he can prove it by listening to AM reception change as antenna rises.

Hope you are right Dennis, he will have a better path there.

John

 

John,

I have an override switch installed, so was able to check things by raising and lowering the antenna while listening, which of course does not disturb the antenna ground connection. AM signal goes away as antenna disappears.

I understand what you were describing about separate AM antenna setups, but I don't think that's what we've got here.

 

Thanks Dennis! Glad to hear it.

For original poster: did you know, you can access the back of radio and its antenna connection from behind down in the footwell? No disassembling required.

Best way to clean this antenna connection? I can't take credit for this, I once had the opportunity to discuss "the best method to clean the pins on my vaccum tubes" with Victor Komenicho(spelling?) the owner/creator of BAT (Balanced Audio Technology), a very high end manufacturer of vacuum tube based amplifiers and audio equipment. His answer was wonderful in its simplicity, I never expected it. It can be applied to everything from our cigarette lighter to your antenna - just plug it in then take it out a few times. The act of doing uses the friction of the connection to wipe the connectors clean of dirt and corrosion.

Let us know how you do!

John

 

Thanks for all the comments. I've triple checked all the grounds, and am reasonably confident in them. As Dennis stated, I get good AM reception with the Antenna up car not moving, No reception with the antenna mast removed from the base, etc. The Only time the reception starts to fail is as I start to drive faster, and the air starts to whip the antenna around (over about 20 MPH). I can duplicate this failure in the garage by moving the antenna to simulate the whipping effect of wind. If I grab the antenna, reception goes down, so I do it with a gloved hand. It is definitely a poor connection at the antenna, and pretty sure it is related to the small press fit cylinder that holds the antenna mast to the antenna base. There are two little cuts in that sleeve with the sheetmetal bent so that you have these two little fingers that can press on the outside of the last section of antenna as it rises, and it's possible that those fingers just don't support the antenna well enough to maintain contact. I'm grasping at why I get bad AM reception at speed, but no issues on FM.

I'll keep researching. May call the mast manufacturer. If all else fails, next step is Sirius XM ....
Thanks

 

Dennis, good call.

Darbysan, glad you have a handle on it.

John

 

Thank you, John.

Darby ... without getting too far down in the weeds, a few things you said make me suspicious of the contact between the antenna base and the skin of the car. Does that seem secure?

 

It is secure, and well insulated via the grommet. One of the first things I thought of, based on issues with other cars I've had, but the Jag design is really good there.

I just got off the phone with a specialist at Antenna Specialties. We discussed how the antenna works, and he suggested a couple of things for me to check, which I will do on Wed. There is a sleeve that fits over the mast and slides down in to the antenna, with 2 fingers. This sleeve, when the nut is applied at the top of the antenna, keeps the antenna from coming back out of the base. Those fingers need to bend outward to assure a good contact with the inside of the upper part of the antenna base. Pretty sure that they are, and that I have good contact, but will check it.

The second thing for me to check is that the antenna makes it's final connection when raised between a very small flange on the bottom of the last section of the collapsing antenna and the lower end of the sleeve mentioned above. The specialist believes that the contact there is not solid, and that the rocking of the antenna is breaking that contact. I'm going to try and raise the sleeve up a little bit ( maybe 1/4") so that the bottom of the sleeve is above the bottom of the corresponding part of the Antenna base, so that when the last section of the antenna comes up, that small flange is making contact not only with the bottom of the sleeve, but also making contact inside the upper part of the antenna. Figure that gives me 2 bites of the apple for a solid contact. Sounds complicated, and may not work, but something to investigate.

 

Update- Fixed. I tried several iterations of getting either of the two new masts to more fully seat within the XK8 antenna body, but no luck. I did get it to work for about 20 minutes, but moving the antenna up / down a few times brought the problem back. I decided to try an aftermarket replacement power antenna, and after install I believe the problem is gone. Need a few more trips to be sure, but no sign of break-up on the AM band, even with aggressively moving the antenna in the garage. Road trip was also good.

Fix would have been easier if I could have found an antenna adapter for the stock Jaguar antenna lead in the trunk, but I was unable to find anything that fit. Eventually, I just cut the leads and soldered in a female Motorola Antenna connector. I used the stock antenna bracket, slightly modified to fit the new antenna ( slotted one of the holes). I used longer bolts with 1/2" spacers to mount the new antenna to the bracket, to achieve the same height at the fenderwell. Used the stock fender grommet. Spliced the wires to the stock antenna power connector, leaving the connector intact for future....

Thanks again to all that contributed. Now on to the next project!

 

Darbysan, congratulations! Dennis, you were right, nice job and than you for teaching me something! Bad news is you get all the antenna questions from now on :-).

John

 

John,

Of all the aspects of "electrical stuff" I've ever tried to learn, antenna theory and fields in general are by far the most daunting. Beyond the simplest cases, much of it is still a black art as far as I can tell. I just trust what's in the books.

 

+1 to all the above

We learn something new even on a 20 year old bit on the car that will always break eventually.

IMHO a photo from the OP would be nice to complete the thread.

 

I also just replaced my antenna with a $20 ebay universal one, as my mast and motor were broken when i bought it.

It really is not that big of a deal and any automatic antenna should be able to fit in the huge spot we have back in the boot for it.

The previous owner was a hack and wing nutted the wires together. I undid those and made proper connections.