[ale] ot - FM transmitter makes good GPS jammer

Tue May 8 09:21:22 EDT 2012

On 05/06/2012 10:37 AM, Ron Frazier (ALE) wrote:
> Hi Jim,
>
> I think I'm just giving up on that particular product / project.  I now
> have a wire running from the tablet's headphone jack into a small boom
> box sitting on the seat.  It works, and I don't have to fret with it.
> It's a shame, because, with the FM transmitter, I could use one less
> piece of relatively large equipment and clear the seat up if the tablet
> is on the dash.  There's no easy way to test the FM transmitter without
> plugging into the cigarette lighter as that's where it gets its power.

I've had two different such FM transmitters and both really provided 
lousy sound.  You might consider replacing your auto sound system with 
one that has an input jack.  That's what I did with my truck.

>
> Sincerely,
>
> Ron
>
>
> On 5/4/2012 4:51 PM, Jim Kinney wrote:
>>
>> Ron,
>>
>> That test doesn't isolate power drop on audio output from signal overlap.
>>
>> to test that the FM transmitter is overlapping the GPS signal, you
>> need a secondary GPS receiver other than the tablet.
>>
>> It really sounds (ha!) like the tablet has a bad headphone jack or the
>> FM transmitter has a fault and is pulling power down the audio line.
>>
>>
>> Try your test again but with the transmitter NOT plugged into the car
>> power jack.
>>
>> On Fri, May 4, 2012 at 3:21 PM, Ron Frazier (ALE)
>> <atllinuxenthinfo at techstarship.com
>> <mailto:atllinuxenthinfo at techstarship.com>> wrote:
>>
>>     Hi Jim, and all,
>>
>>     I've tested this several times and confirmed the behavior.  It's
>>     definitely not power.  Today I tested this as follows with the
>>     tablet running on battery power.
>>
>>     I start the tablet on battery power and run a program called GPS
>>     test.  I get a nice clean fix on 5 - 6 satellites, a positional
>>     accuracy of 15 ft or so, and SNR values in the 26 - 31 range (this
>>     program doesn't specify the units).  Those satellites are color
>>     coded in yellow by this program.  I have a podcast playing in the
>>     background on the tablet's internal speakers.  I have the fm
>>     transmitter plugged into the cigarette lighter but the AUDIO cable
>>     is not plugged into the tablet.  So, sound is coming from the
>>     tablet's speakers, and nothing is coming from the car's speakers.
>>     Everything is fine.  GPS works.
>>
>>     I plug the AUDIO cable in from the FM transmitter into the
>>     tablet's headphone jack.  Sound starts coming out of the car's
>>     speakers, as it should.  Immediately, SNR's for the satellites
>>     drop below 20, satellites with a fix drop to 0 - 1, and the
>>     position fix is lost.  I've confirmed this several times.  It is
>>     exceedingly strange.
>>
>>     I've officially fired the FM transmitter.  I don't think I have
>>     the packaging to take it back to Fry's.  It's a NAXA NA-3029 if
>>     anyone's interested.  I'd recommend avoiding this unit.
>>
>>     I've gone back to my old method.  I have a boom box with aux input
>>     sitting in the seat, and I run a wire from the tablet to the boom
>>     box.  Messy, but it works.
>>
>>     Sincerely,
>>
>>     Ron
>>
>>
>>
>>
>>     On 5/1/2012 8:19 AM, Jim Kinney wrote:
>>>     that sounds more like an internal power issue. The device draws
>>>     more power on a bus that is available for both the gps and it to
>>>     run to gps falls down.
>>>
>>>     To see if it's actually radio interference, check you cell phone
>>>     gps next to it and see if it also chokes.
>>>
>>>     On Tue, May 1, 2012 at 12:20 AM, Ron Frazier (ALE)
>>>     <atllinuxenthinfo at techstarship.com
>>>     <mailto:atllinuxenthinfo at techstarship.com>> wrote:
>>>
>>>         I have one of those cheap fm transmitters that broadcasts
>>>         audio from a
>>>         portable device to the car stereo.  It works great to send
>>>         sound from my
>>>         tablet to the car.  However, it also jams the tablet's GPS
>>>         system.  When
>>>         I plug in the transmitter, the number of satellites the
>>>         tablet has a fix
>>>         on goes from 6 or more to 1 or zero immediately.  The GPS
>>>         fails to
>>>         work.  If I unplug the fm transmitter, the GPS works again.
>>>          Anyone ever
>>>         seen that happen?
>>>
>>>         Ron
>>>
>>
>>
>> --
>> --
>> James P. Kinney III
>>
>> As long as the general population is passive, apathetic, diverted to
>> consumerism or hatred of the vulnerable, then the powerful can do as
>> they please, and those who survive will be left to contemplate the
>> outcome.
>> - ////2011 Noam Chomsky
>>
>> http://heretothereideas.blogspot.com/////
>
>
>
> --
>
> (To whom it may concern.  My email address has changed.  Replying to former
> messages prior to 03/31/12 with my personal address will go to the wrong
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>
> (PS - If you email me and don't get a quick response, you might want to
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>
> Ron Frazier
>
> 770-205-9422 (O)   Leave a message.
> linuxdude AT techstarship.com
>
>
>
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-- 
Until later, Geoffrey

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