How can I decrease FM reception for my car?

September 28, 2006 10:42 AM

How can I decrease FM reception for my car? I have taken off the antenna, but would like to proceed further.

So, I have a new Sirius receiver and it broadcasts over whatever FM frequency I choose to my car radio. However, my area seems to have a lot of stations, with strong signals, so I get a lot of interference.

Obviously, I can just hardwire the receiver to the radio and this will solve my whole problem, but I was wondering if there was another step I could take in reducing the FM reception. Removing the antenna helped, so I was wondering if obstructing the remaining base it screws into would help. What material would dampen FM signals? Can I effectively reduce FM signals from the outside world but not one coming from inside my car, or is my whole car one big antenna?

posted by poppo to technology (17 answers total)

Can you reach behind the radio and disconnect the antenna lead? It's remarkable enough that you're getting reception inside the metal body of the car, but nonetheless the antenna lead itself can make a fairly effective antenna.
posted by zek at 10:45 AM on September 28, 2006

(getting reception inside the metal body of the car -- of the city FM stations)
posted by zek at 10:46 AM on September 28, 2006

Hardwiring is a fairly cheap afternoon project if you have access to a garage. If not, It's still not much more than $50 for parts and labor from your local Circuit City type installer. Anything else is going to be an utter waste of time and money that leads to other problems.. like cutting off your hand because you can't stop eating Oreos.
posted by kcm at 10:59 AM on September 28, 2006

Zek: Well, then I'll get zero fm reception, won't I? I need a little to pick up the signal coming from the Sirius device in the car.

Also, if I take the dash apart and reach behind the radio, i might as well just hardwire the receiver. This may end up being the solution, but I was hoping for something less invasive.
posted by poppo at 11:00 AM on September 28, 2006

poppo,
I really suggest you get it hardwired or if you don't care about a bunch of wires running down your dashboard - like me!- and your car is so old or no frills that it still has a tape deck -like me!- you get one of those Radio Shack line in to tape deck adaptors for 11 bucks. The short range radio broadcast deal just doesn't work well in big cities with crowded radio dials and it degrades the sound of your nice Sirius radio most of the time.

However if you want to get nutty you could - if you can find and/or reach it - cut the antenna lead so that only a tiny bit protruded from the back of the radio and then put the sirius box as close to it as possible, but why do that? If you got the little cheap one I got, watch out as it gets super hot almost instantly.
posted by Divine_Wino at 11:09 AM on September 28, 2006

In other words you are always going to get some reception and bleedover from other more powerful FM sources on the same frequency and that happens a bunch more in places with lots more fm transmitters.
posted by Divine_Wino at 11:11 AM on September 28, 2006

Ok, gang, seems to be a consensus: Only way of reducing FM reception is to get at the lead from behind the radio. In that case, I'll just run a wire, no big deal.

I was just thinking maybe I could stopper up the antenna base with a rubber plug or something.

Thanks!

I'll be back later to check for any latent magical solutions.
posted by poppo at 11:13 AM on September 28, 2006

you get one of those Radio Shack line in to tape deck adaptors for 11 bucks.

I've found that ditching the FM receiver idea entirely, and going with the tape adapter is 1) non-intrusive to your radio wiring and 2) much better sound quality overall than the FM option.
posted by thanotopsis at 12:38 PM on September 28, 2006

Due to something called the capture effect, the strongest FM signal wins when two similar or close frequencies compete... thus, an alternative is to get your transmitter antenna closer to your radio antenna... You may still get some dropouts when driving right by a powerful station, but it should be less frequent.

If you are driving in the same area all the time, perhaps you would benefit from getting a list of the specific FM stations in your immediate area.

http://www.radio-locator.com/ lists close FM stations by zip code.

Use this list as a guide to choose the weakest of the stations and decrease the distance between your Sirius and what remains of the stub in your antenna and see if that helps.
posted by FauxScot at 1:24 PM on September 28, 2006

Ok follow up so far:

-Tape adapter won't work as it's not a tape deck, but thank you
-I've yanked the radio out and the only input it has is for the antenna, i.e., no auxiliary type input.

So here's my next question, regarding hardwiring it I guess. I could get this, sold for exactly this purpose. However, I have one wire that came with my purchase with the line-out adapter on it, and I obviously have the input from the car antenna.

Can't I just splice these two together and avoid buying this thing? Of course, I will no longer have an antenna for public FM broadcasts, but I don't care.
posted by poppo at 1:35 PM on September 28, 2006

"... However, I have one wire that came with my purchase with the line-out adapter on it, and I obviously have the input from the car antenna. ..."

The antenna wire basically delivers radio frequency signals to circuits inside the radio that are both designed to reject audio frequency signals strongly, and to greatly boost the amplitude of radio frequency signals that they do receive from the antenna. So connecting an audio line out output directly to the antenna input wouldn't accomplish anything useful, and could damage your radio.
posted by paulsc at 3:17 PM on September 28, 2006

If it means anything to you, the FM transmitter only sends a mono signal out. If you do get it hardwired, it will sound a lot better. I don't notice with talk radio(stern), but music doesn't sound too great in mono. And, my sportster replay came with a small FM antenna lead which you're supposed to hook up to back of the receiver to send out a greater signal if need be.
F Jackie!
posted by phox at 5:02 PM on September 28, 2006

The antenna connection can be hardwired. The connector goes in between your antenna's cable and the input jack on the deck, so that it overrides the antenna with the signal coming from the XM unit when one is sent.
posted by kcm at 5:14 PM on September 28, 2006

I've yanked the radio out and the only input it has is for the antenna

Just a sanity check here, but if you've already yanked out your radio out, couldn't you just replace it with a cheap unit from the store with either a tape deck or an auxillary input?
posted by thanotopsis at 6:44 PM on September 28, 2006

Personally, I'd visit a pawn shop / Junk Yard and try to find a cheap-o radio with aux-inputs.... $10 and you're good to go.
posted by hatsix at 7:28 PM on September 28, 2006

Ok, so splicing is out, thanks paul and phox.

In that case, as suggested above, I will either:
a) get a different radio, if i find one at the pawn shop for less than $20 or
b) get the $20 FM modulator

I'll be back with an update later
posted by poppo at 6:52 AM on September 29, 2006

I got the FM modulator...It works great. Thanks everybody.
posted by poppo at 12:29 PM on September 29, 2006