Understanding the Next Generation of Satellite Radio FM Transmitters

Friday, October 13, 2006 at 1:51 PM
Tags: 2, XM

With the FCC's crack down on FM modulators exceeding emission levels a new alternative needed to be created that satisfies two major criteria: 1) the FM signal can't "bleed" to other vehicles and 2) it needs to provide the best user experience possible. None of these factors are negociable.

Enter the next-generation of FM Transmitters for satellite radio. Both XM and SIRIUS have very similar approaches: localize the transmission as close as possible to the car's pre-existing antenna.

The next obvious approach is to hard-wire the satellite radio directly to the headunit, but that's asking a bit much from the consumer. That's not to say that running wires all over your car should be considered an easy task for most consumers, but this is a good compromise. The Big Box Retailers with installation services are going to be loving this by the way, because these extra FM wires are going to entice the consumer to go with a professional installation (which provides an upsell opportunity to go with the hard-wire approach).

But enough with this palaver, on with the modulators...

Vehicle Antenna Locations
Here you'll see the most common locations of a vehicle's FM antenna. External locations include numbers 1-4 (front fender, rear fender, front roof-top and rear roof-top - these can be either the retractable or fixed "aerial" antennas, or those fancy "shark-fin" ones you see). Internal locations include numbers 5-7 (which are the inside-glass versions that look like a window defroster - #7 specifically shows how some SUVs/Mini-vans will be located in on the side-windows).

The separation between Internal and External are important, because this is where XM's and SIRIUS' approaches with their FM Coupler and FM Extender differ. See a whole lot more on this after the jump...


SIRIUS FM Extender
First let's look at SIRIUS' FM Extender. This was discovered as part of the new FCC certification for the SIRIUS Sportster4, and I assume this will be used across the board as the FM transmitter of choice for the rest of Sirius' car-based receivers.

SIRIUS FM Extender 

The parts involved are simple. The main FM Extender Cable, as well as 2 suction cups and 3 self-adhesive cable guides.

SIRIUS FM Extender
The suction cups are meant to allow for temporary placement of the FM Extender wire so you can test how it sounds.

SIRIUS FM Extender
Then using the self-adhesive pasties, you can permanently attach the FM Extender to the inside of your glass.

Depending on the orientation of your car's antenna, you have several different configurations that give you the best performance for FM transmission.

SIRIUS FM Extender
In the above diagram you see a front and rear fender ("aerial") antenna, and the SIRIUS FM Extender is located vertically. Makes sense. Got a vertical antenna? Then mount it vertically. (Note: some states don't like you putting things on your windows, so you'll need to attach the FM Extender to the pillar closest to the antenna - shown in the first diagram).

In cases where you have a rear roof-top FM antenna, you should mount the FM Extender horizontally on the edge of the glass:
SIRIUS FM Extender

The same orientation applies for antennas that are either front roof-top, those fancy shark-fin style antennas, or inside-glass FM antennas (not pictured).

If you happen to have one of those SUVs or Mini-Vans with the in-glass FM antennas located on the side, your installation would look like this:
SIRIUS FM Extender 

And that's it for SIRIUS' solution.

Now let's compare this to XM's FM Coupler (which I believe is being called "Sure Connect").

XM FM CouplerXM's FM Coupler
We first learned about the FM Coupler from XM's recent certifications which came with a handy manual.

Again, the concept is similar - bring the FM transmitter and antenna closer to each other - but XM is directly attaching the two with the coupler.

To the right you'll see the hookup to the radio is the same, but that there's a "coupling module" in-line where the FM transmitter cable and the satellite radio antenna split off (previously the FM signal was transmitted through the antenna cable itself).

At the end of the FM transmitter cable (labeled "output cable" on the right) is the coupler-clip with two different configurations for internal or external antennas.

XM FM Coupler
For external antenna, the coupling clip attaches directly to the base of the antenna. Whereas for the internal antenna the coupler is attached directly to the on-glass antenna.

XM FM Coupler
Here you can see different configurations of the FM Coupler and the XM antenna locations.

XM FM Coupler
Simply attach the coupling clip, and then use the boot to secure the clip to the antenna.

XM FM Coupler
For the in-glass antenna installation, you first should adhere the contact bracket directly onto the car's in-glass antenna, then you attach the coupler to this bracket. It's important to note that you should make sure it's the car's antenna you're attaching to and not the window's rear defogger... because, afterall, that's not the antenna.

And that's the XM method.

Now let's argue over which is better. Obviously the answer is "neither" because, as with anything in engineering, it's all a compromise. SIRIUS' solution is easier to install because you don't need to go outside of the vehicle if you have an external antenna. That said, SIRIUS' installation is a bit bulkier for internal antennas when compared to XM's. XM's external boot loses points for the ugly-factor. That said, XM doesn't need to transmit nearly as much emissions as SIRIUS does with their solution because the coupler is directly attached to the antenna rather than just closer. I said it was all a compromise didn't I?

[SIRIUS FM Extender Manual (PDF)]
[XM FM Coupler Manual (PDF)]
[both via the insightful eye of Satellite Radio TechWorld]



I think they both stink. The Sirius one looks like it will be more noticeable. However, if FM mod is the only way to get sat radio in your car, you will make the sacrifice for the sat radio provider you choose. I don't think either alternative will drive consumers to the other. I now have my XM Commander hooked up through an aux input in my new Saab -- that is the way to go. The sound is amazing.

I'm sure the NAB will complain about this somehow.

Not to mention the XM boot method won't work with power antennas, or if you take yours off to go through a car wash, or like me, got rid of it since all you listen to is XM (and a dove bent the crap out of it at 75mph on the freeway).

Sooooo when are the mp3 player accessory makers going to have to have this done?


Damn Dandy.

Another confusing reason to discourage the only real selling sector of satrad.... retail.

Why don't we just make 1,000 radios a year, charge 100 per month, and require that they be installed by golden monkies who are UAW members and activated by CS reps on both sides who aren't authorized to answer their ringing phone.

Let's pay Howard 1 billion and see CFBE in 2010 and the first real profit dollar in 2020.

Satrad.... it continues to be an ass pain.

They look crappy -- particularly the Sirius one.

But the truth is that both will likely sound better than the previous wireless mods ever did.

XM has already said they intend to "incentivize" the professional installers in Q4.

It is just one more reason for more people to consider OEM installs.

This is why my dad returned his SkyFi that I got him for Xmas. The average person just wants to get a radio, turn it on and it works. Until both companies make this simple, the retail numbers are gonna be shit.

I think XM/Sirius should protest these lowered standards by something like a petition... If this is what they've got, I'm not really too sure what the outlook will be in the coming years.

How about protesting the idiot automakers that still don't provide an aux-in jack as a standard feature?

How long have we had handheld Walkmen/Discmen/CD Players/Mp3 Players now? 20 years?

Like there wasn't enough of a hassle installing plug and play receivers to push away buyers on the fence? Wow. This is such a hassle, even I probably won't try and set it up, and I'm a geek. TOO MANY WIRES AND TOO MESSY.

I am all for technology that improves the environment and a radio transmitter that that lowers emission levels is a great idea and the way the world needs to move with this and many other devices that emit to many high levels of radio waves.

I am all for technology that improves the environment and a radio transmitter that that lowers emission levels is a great idea and the way the world needs to move with this and many other devices that emit to many high levels of radio waves.

Wow. Please tell me you're not serious..

Man, this is crap. I just bought a Pioneer INNO2BK at Circuit City and was going to wait on the car kit. They did tell me that the install price was $79.99 (up from $39.99 on the INNO1) but I didn't realize why. What a crock. AND I've got a power antenna on my maxima. Does that mean I'm screwed and can never have a car kit?!? This is depressing.

Not knowing a lot about satellite radio and after my family gave me one (Xpress XMCK-10A with sure connect) for Christmas I started to read different wed site for reviews, I almost return it back to the store because most people said it was a difficult to install. However after about one hour of studying and about 2 hours of taking my time running wires in my 2005 Dodge Ram my wife and daughter gave me thumbs up. For this vehicle it is very easy and it neat looking installation process, no wires are showing only the lighter wire, even the connection for the antenna was a clean and neat hook-up.

I have a 1998 Cadillac with carrage top and an elec. ant. My magnetic ant. is on the hood and I hooked up my sureconnect was routed to the ant. in the trunk. I hooked the module up to the ground wire of the ant. and ran the wires back to the receiver. I have good reception anywhere I go. Not too difficult a job, just tedious. Took about 30 mins.
Big Q, in Colorado.

I want to just say goodbye to sat radio...I tried to hook it up in my ford explorer and all i hear is static. Its so dissapointing that I spent all this money. Someone needs to blow up the FCC and let these companys conduct business freely. Fuck The FCC, Fuck FM radio, Fuck musicians and all those others who have a problem with stealing music.

I have an XM radio that utilizes the "Direct Connect" method and I think that it works wonderfully. I am not unfamiliar with running wires in cars so I did the install myself.

I can see how most people not wanting to run these wires themselves and not wanting to pay someone to do it may drive them more towards the Sirius models but like the article says, it's all a compromise.

We use one on my wife's car. It's a Mazda5... no aux-in jack*, and the antenna is on the trailing edge of the roof.

Because of the distance between the XM receiver and the antenna, it was unlistenable using the built-in receiver. The thick rubber boot on the base of the FM antenna seemed to preclude using the Direct Connect; however, a momentary stroke of clarity led me to simply clamp the coupling clip directly onto the antenna wire. No ugly wires, the cooupling clip is hidden behind the headliner, and it works perfectly.

* this would've been a deal killer if the car wasn't so one-of-a-kind. We weren't even thinking of XM at the time, but rather MP3 players. When I bought my Element, I got hooked on the XM, and we ordered an Audiovox tuner as part of a promotional deal when we extended my subscription.

There is an aftermarket product called AuxMod that adds an auxiliary jack to the factory Mazda stereo. However, tearing the dash apart is much more a pain in the bumper than simply popping off a piece of trim in the back. Replacing the head unit itself would've also been a pain due to the non-standard design and losing the steering wheel controls.

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