In the Porsche car configuration there is an option for a rod antenna. What advantage, if any, is there to that? Do you get better reception? Really more curious than anything. Thanks.

 

I hope someone actually knows because I'm curious myself. A conventional car antenna, a rod, is technically known as a monopole antenna. It uses the car body as a ground plane. Great for the usual AM transmission frequencies and not bad for FM either. And you can adjust them to optimize reception of the stations most important to you.

What I know about the embedded antennas in car windows you could put in a much shorter sentence. "Not much." Or "Diddly squat." Still two words. Oh yeah. Lots shorter. Could they be a folded dipole?

Since Porsche offers the option, I infer they are less effective in some areas or for some transmissions that some customers want to hear. (Doesn't everybody have XM by now? Uh... no, suppose not.)

Inference is not knowledge though. Come on, people. Does somebody actually know? Or must I hustle off to one of my other lists to inquire?

Gary

 

The rod antenna is for AM.

 

That option is to improve AM radio reception.

The nature of the AM channel frequencies is that to pick up the signal well, you really need a solid stick antenna.

So if there is AM stuff you really want to hear cleanly in weak AM areas, the rod antenna is what you need.

AM reception is much weaker w/o the rod antenna, but the thinking is most radio use these days is SAT and FM based.

 

I asked some of those other friends. One is an engineer who has designed antennas, as opposed to my rather blind faith application of them as black boxes in my designs. He said:

So we do have a difference in effectiveness as an antenna for AM reception, as expected. The term "quarter wave" by the way, refers to the length of the antenna compared to the wavelength of the radio frequency being tuned. The line about getting stuck under overpasses is heavily tongue in cheek since the center of the AM band has a quarter wavelength of 75 meters or 246 feet.

In fact, we not only wind the wire as described but also trim it electronically so it reacts like a quarter-wave even at other relatively close frequencies.

A guy with receiver experience added this observation:

A 246-foot rod antenna would in fact clear the tallest structures around most of Southern California, but I don't think he meant that example. His point about modern receivers has a subtle significance that may not be apparent. AM modulates the information as changes in signal strength. When the signal weakens, the volume drops. When it grows strong again, the volume can rise painfully. Short term fluctuations change the quality of the sound as well as the volume. This is probably the biggest reason for FM becoming popular for fine music in the early days. Now, just as AM is about to fade permanently, we have radios able to compensate to a large degree for those variations.

Now putting together these two responses, we have the reason for the rod antenna option in the Porsche configurator. In some parts of the world, AM transmissions are still the dominant medium. Owners are not within the footprint of any satellite sources; FM won't cover the distances involved from the stations and their limited transmitter sites; and the car will be operated at distances from the source where even a modern computer-based AM receiver cannot always separate signal information from signal fluctuations. That means the strongest possible signal needs to be acquired and with as few causes as possible for fluctuations in strength.

All that means a rod antenna. Hence the option. Rather like the engine computer's tolerance for ghastly gasoline. Not what you want, but what you must.

Gary

 

Uh, what he said. If there was ever a post that deserved added reputation points; I would have to say that was it. I guess in plain English, I would expect most 997's driving around Kandahar have rod antennas!

 

Yes! That's what I meant! Much more concisely expressed.

 

Interesting!

I was just about to post a question why the AM stations are barely audible on my recently acquired '09 997.2. I have XM but it's nice to be able to access local AM. My BMW M-Roadster has a rod antenna with the above mentioned coiled winds. I never realized that the coils were functional vs. decorative. And AM comes in crystal clear.

Any other options to improve AM reception other than a stick antenna?

 

I can ask, but honestly I doubt it. Will inquire though.

Gary

 

Not that would result in something far less attractive and much more expensive to a rod antenna.

 

As mentioned.....a 997.2 without rod will not even get local stations well.

The other known A.M. radio shortcoming is the 'FM switch'......shut off car while listening to A.M.....get back in, fire up.....and radio is in FM.

 

It depends where you are located. FM tends to propagate line-of-sight and you get local stations well with good capture ratios. AM propagates longer distances, can benefit from ionosphere bouncing but it is more affected by noise and interference. The larger AM stations are far more powerful than the little transmitters used by FM. In CA the large AM stations CBS, ABC, and NBC are heard loud and clear pretty much anywhere in a 911 with the bult-in antenna.

For those who replaced windshields make sure the antenna (which is embedded in the glass) was connected correctly.

 

Well, on the bright side, it is a no cost option. I suppose it wouldn't hurt the resale to have it and it certainly can't weigh much.

 

I think it would hurt resale. I think most would consider it an eyesore and explaining that it improves AM reception won't win many points.

 

I did ask my friends more experienced with analog radio issues. The consensus is that you need to:

1. Listen to stations with greater signal strength in your area, c.f. the reply from Adias;
2. Check for and improve the grounding connections on your hypothetical 'older' car, which clearly doesn't help the owners of the 2009 997.2, like you and me. Never hurts to have the dealer check the antenna connection at both ends, but don't hold your breath;
3. Install a rod antenna.

Personally, I'd say the aftermarket rod antennas are not unsightly so long as you get one that retracts and have it wired to extend only when you select AM on the control head.

As for the "FM switch" Gregg mentions, it annoys hell out of me. I'll be listening to some CD at an appropriate volume level, remove it after the last track and forget to turn the volume essentially off before hitting the eject button. The damned radio does not revert to my usual XM choice, but instead goes to the FM. That section outputs a line level that is easily ten db higher than the CD player and seems more like thirty, unlikely as that is. I never listen to FM out here in the desert and the distasteful station the radio randomly chooses to bellow at 110 decibels always reinforces my opinion that jackhammering our driveway would be more entertaining than the locally available FM.

A half dozen other examples of poor control design demonstrate that when Marketing insists that even a performance car needs a "hi-fi" installed, the design team should pick an intern who actually listens to radio for the dash down to Woolworth's 5 & 10 to pick one.

And don't get me started on the soi-disant "navigation system" that proposes I take my lovely Carrera out across the desert as the most convenient route into town.

Never mind. I didn't buy the car for those features. I can always turn them off and enjoy the car for itself.

Gary, who wonders which store near Zuffenhausen would
be the German equivalent of a Woolworths five and dime