[ale] ot - FM transmitter makes good GPS jammer

Jim Kinney jim.kinney at gmail.com
Sun May 6 19:13:36 EDT 2012


Last tast: plug the transmitter into a different sound source like the boom
box. I'm betting the fault is with the tablet.
On May 6, 2012 10:37 AM, "Ron Frazier (ALE)" <
atllinuxenthinfo at techstarship.com> 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.
>
> 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> 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> 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
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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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