[ale] ot - FM transmitter makes good GPS jammer

[Jim Kinney]

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
>>
>>
>
>
> --
>
> (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
> address.  Please send all personal correspondence to the new address.)
>
> (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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-- 
-- 
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/
*
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