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Author Topic:   Garmin 540s and Garmin GXM 31 Antenna
BellBoyBob posted 06-27-2008 10:10 PM ET (US)   Profile for BellBoyBob   Send Email to BellBoyBob  
I am planning to subscribe to XM for their marine weather service and I will purchase the GXM 31 antenna. I notice that my particular subscription comes with XM radio as well as weather. How would the antenna connect to the on board audio system for radio playing?


jimh posted 06-27-2008 10:20 PM ET (US)     Profile for jimh  Send Email to jimh     
An antenna does not produce audio output. The GXM 31 must be something more than an antenna if it can produce audio outout.
bluewaterpirate posted 06-27-2008 10:42 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
The GXM 31 Smart Antenna provides both output sources for XM Weather and Music. It is self-contained control unit similiar to the Garmin GDL 30A. The 500 series chartplotters display the weather and are used to select the music channel you want to listen to.

Here are two pictures of the Garmin 545 and GX31 Smart Antenna. 4892322_2159358_31003902_WebSmall_3/ Image-4892322-31003902-2-WebSmall_0_3c80b21ddfeec780aac6894dd235e183_1 4892322_2159358_31003912_WebSmall_3/ Image-4892322-31003912-2-WebSmall_0_cdc808aa346fb2363fb67649d477ff78_1

The rca connectors in the second picture connect to your radio's aux channel and provide audio output from the GXM 31 Smart Antenna. The 540 and 545 are used to control what you listen to but cannot reproduce music to listen to via the Garmin chartplotter.

Here's video that shows the relationship between the Garmin 545, GXM 31 Smart Antenna, and your installed stereo radio.

There you go.


jimh posted 06-27-2008 10:59 PM ET (US)     Profile for jimh  Send Email to jimh     
It sounds like the Garmin GXM 31 SMART ANTENNA is actually a radio receiver. A radio receiver captures and amplifies radio signals, then it demodulates them into baseband signals like audio.

I browsed the GARMIN website, and I see why there is confusion. They don't explain much about the GXM 31 Smart Antenna AKA radio receiver. It is a good thing we have Tom here to explain their product line for them.

BellBoyBob posted 06-28-2008 05:27 PM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
I see, Tom. What was missing, as jim said in the literature about the GXM 31, is any reference to the interfacing of the GXM 31 to the radio's input via RCA jacks. One other question: Is the reason the XM option does not appear under the config. menu because I don't have the antenna plugged into the back of the chartplotter?


jimh posted 06-28-2008 05:43 PM ET (US)     Profile for jimh  Send Email to jimh     
I also wonder if the receiver circuitry is really in the GXM31 SMART ANTENNA. Perhaps the receiver is really in the Garmin 540s and the presence of the GXM 31 just unlocks that little secret.
bluewaterpirate posted 06-28-2008 07:22 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Nope ... the antenna is the receiver and pass thru device for the XM functionaluty just like the GXM 30 Smart Antenna. The GXM 30 Smart Antenna connects to the Garmin 376c or 478 and provides XM functonality for these devices. 4892322_2159990_31018890_WebSmall_3/ Image-4892322-31018890-2-WebSmall_0_b98fe15280ce2841b60439780171349d_1


bluewaterpirate posted 06-28-2008 07:47 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
The GXM 31 comes with an owner's manual but for some it's not availabe online. Here is the GMX 30 Smart Antenna Owner's Manual. GPSMAP3005C_GXM30forMarineProductsOwnersManual.pdf

When you connect these antennas to their respective units the antenna is recognized by it's unit ID Number. During the XM activation process the smart antenna id number is validated by XM's equipment. Once the smart antenna is validated then it looks for the Garmin unit it is attached to. Once the Garmin unit is validated it is tied to that smart antenna until you notify XM that you are terminating their service or connecting to another Garmin unit.


bluewaterpirate posted 07-01-2008 09:48 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Here's a video of the XM/Unit ID Info display.


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