Rednroll

Aftermarket GPS antenna's are given the extra length of wire, so they can be mounted to the outside of the vehicle, therefore no obstructions between the antenna and the sky, therefore a stronger GPS signal reaching the antenna, therefore less concern for the extra cable length.

http://www.youtube.com/watch?v=NZ4WvTZDF3U Now let's use some common sense reasoning.
- The JK has a Sirius (SAT Radio) antenna mounted above the sound bar
- This SAT radio antenna obviously has a long cable run, since the other end of the cable connects to the radio.
- There's room available on the other side in that sound bar area to be able to mount a GPS antenna, like you are doing, where Chrysler could have done the exact same wire run, etc. as they did with the SAT antenna.
- For some reason, Chrysler decided to not do that but instead put a GPS antenna mount with a shorter cable run right above the radio instead of in the mounting area as the Sirius SAT radio antenna.

Do you think there's some possibility that Chrysler may have discovered that area might not be a very good area for a GPS antenna? I'm not saying it won't work...I'm just saying it doesn't seem like the best mounting area.

As I mentioned earlier GPS Sat signals are lower in signal strength than SAT radio signals. In fact GPS SAT signals were originally developed by the U.S. government for military purposes. Their original intent was for these signals to be undetectable by the enemy. Some years later the government made these GPS signals publicly available for these navi devices we all now have. Nothing was changed to make their signal strength stronger. If you have ever looked at a GPS SAT antenna signal like I have on a Spectrum Analyzer, you will see it is buried in a noise floor surrounded by noise, where in most instances the surrounding noise is higher in signal strength than the actual GPS signal. You would not know it's there unless someone told you exactly what to look for and that's what a Navi device has been designed to do. Now SAT radio, it's original intent was to broadcast audio radio stations. There's only 2 Satellites that get used for SAT radio, which go by the names "Rock" and "Roll". However the signal strength is stronger for these radio broadcasts, than the GPS signals because their original intent was for them to be heard...not like GPS signals where their original intent was for them to be hidden. So that's why a GPS antenna mount is a little more critical than a SAT radio antenna mount. Thus, it's probably not a good idea to mount that GPS antenna, where the signal has to penetrate the thickness of hard top, which may have some metal materials in it to make it more rigid. It's also not a good idea to use a long wire run, where the signal is further reduced through the length of the wire. It's also probably not a good idea to mount it above a speaker, where the large magnetic field generated by the speaker could interfere with such a weak signal.

I'm not saying it won't work....just a lot of not so good ideas, starting to add up to possibly become 1 bad idea.

JK-Ford

Thank You Sir for taking the time for your explination.

I think they did it to save money on material and labor. Not much for 1. But a lot for 1000.

I'm thinking that there is not a whole lot of differance between the thickness of the Roll Bar Pad + Hard Top when compared to the Dash Panel + Window + Window Frame ( and maybe Hard Top too depending on the orrientation of the vehicle when compared to the satellit position ).

The large metal gusset ( over the speaker ) that the antenna is stuck to should play some roll in altering the magnetic field around the speaker.

Once again, Thank You for the information. Since I have no instrament to measure signal clarity, I'll monitor the "refresh rate" of the screen. And compare the speed and accuracy with a topless Jeep as weather conditions permit.

suds1485

The 2012 is a combo antenna navi and sat radio on the b pillar.

AtlJeepsTer

The Combo Antenna for RHB and the RHR infotainment units are in the same spot as the Older Sat Radio Antennas. Over Passenger seat On Top of The Sound Bar, Same size, Same design ...Looks exactly the same as older Antenna (Sat Radio).

JK-Ford

I have intended to update this thread for a couple weeks. Thanks for bringing it back up. I was exploring the pages on my new HU and found the Sat Signal Strength page. And I was surprised at the quality of reception that I was recieving. Anywhere between 9 and 11 birds registered on the page. All maintained 100% signal strength except for the two or three on the horizon. An average of 6 birds maintained 100% signal strength at all times. It's my understanding that the unit only needs 3 to do it's job.

Just FYI.

AtlJeepsTer

That's pretty damn good...lol...
The RHR can Handle up to 16 Satellites...

The basics for GPS are;

GPS satellites live in very precise orbits about 16,000 km up (for comparison, the space shuttle orbits at about 320km and geosynchronous satellites orbit at about 38,600km). Because the satellites are so far away, their radio signals are fairly weak. Therefore, for the GPS receiver to "see" a satellite, the satellite must be above the horizon and unobstructed by buildings, mountains, etc. At any given moment at any point on the planet there are between 6 and 9 satellites above the horizon.

The GPS system depends on two things to make it work: First, each satellite has an on-board atomic clock that gives it an extremely precise time base. The satellites send radio signals to the receiver, and the extremely precise time bases make it possible for the receiver to determine exactly how far away each satellite is.

Satellite Distribution


The receiver is able to calculate exactly how long it took for the signal to travel from the satellite to the receiver, and from that time determine the exact distance between the receiver and the satellite.
Second, each receiver has stored in memory an almanac that indicates exactly where each satellite is in its orbit at any given moment.

The almanac is possible because of the extremely precise orbits flown by the satellites.
Since the receiver knows exactly where each satellite is (from the almanac) and exactly how far away each satellite is (from the radio signals it receives), the receiver can calculate its exact location in space. There are a couple of extremely interesting problems that have been glossed over here however.

For example, a $250 hand-held GPS receiver certainly does not contain an atomic clock itself, so how does it synchronize itself with the satellites? It turns out that the radio signals sent by the satellites contain extra information that allows a receiver to derive the exact time from the radio signals it receives.

The receiver must be able see multiple satellites for this algorithm to work, but what it means is that once a GPS receiver has locked on to 3 or more satellites, it is itself functioning with atomic clock accuracy. For more details on this trick and many others, see the first article in the Links section for an explanation.

AtlJeepsTer

GPS signals are a Lower Frequency then Satellite Radio and the lower that number the better/stronger the signal....This is not an Opinion, This is Easy to find Facts:

Is there a general rule that the lower the frequency bands the better and that higher bands don’t work as well for wireless?

The lower the spectrum the better able it is to penetrate buildings AND to cover distance. Thus, the current spectrum bands occupied by TV broadcast bands go further and penetrate buildings better than bands located higher in the spectrum. The higher the bands, the shorter the distance a signal travels before it “fades,” and the more it can be impeded by obstacles like foliage or even humidity in the air.


[h=1]Why do lower frequency radio waves penetrate buildings better than higher frequency waves?[/h] For instance, 800 MHz has a much higher rate of penetration than 1.3 GHz.

JK-Ford

Thanks man. Very informative.

Rednroll

It's obvious to me now, that I've somewhere ruffled your feathers and you now feel the need to troll my posts in an effort to try to discredit them. It makes a lot of sense to me now, since you previously went out of your way to dig up a month old argument in another thread discussion that you originally had no part in and the tread was already dead and gone, just so you could stir sh*t up unnecessarily.

So if it makes you feel better to now look up all the threads I've posted in, and go behind me and post nonsense then so be it. In threads like this one, it is obvious to me that you are trying pretty hard to come across as knowing what you are talking about by throwing in just enough technical information to legitimize the information you're posting but just to let you know, the "bullsh*t" you're posting is nothing more than that....."bullsh*t".

In the post you quoted, I gave a simplified response to the differences between GPS and Satellite radio signal strengths. While the things you do talk about do hold some weight in regards to a frequency's wavelength, where the lower the frequency does in fact allow for material penetration more easily it holds very little weight in what I was discussing in regards to the differences in signal strength. You totally ignored the point I made which is in regards to the "signal strength" differences when comparing the 2 signals. While you mention frequencies....frequency, measured in the units "Hz" is not related to the signal strength of that frequency. A lower frequency does not make a signal stronger like you state. Signal strength is measured in amplitude by the units "dBm" for air broadcast signals. Which when you graph out frequency vs. Amplitude, puts the frequency(Hz) on the X-Axis and Amplitude (dBm) on the Y-Axis. So I find it pretty ironic, that I'm specifically talking about the Y-Axis signal strength when comparing GPS satellite signals to SAT Radio signals, while you're creating some other counter argument based on the X-Axis qualities of those same signals while not even addressing the signal strength differences that I had originally outlined.

If you had actually done some homework before posting your argument you may have realized that Sat Radio signals, measured in clear-sky condition's, their signal strength at a receiving antenna measure around -50dBm. While at the same time a comparable measurement of GPS satellite signals measure around -130dBm. Additionally, SAT radio signals also have repeater terrestrial signal setups to additionally help their signal strength. Something not used in GPS transmissions.

Anyhow given that on average SAT Radio is measured to be around -50dBm and GPS signals are measure to be around -130dBm, that comes up to be SAT radio is +80dBm stronger than GPS signals which makes your point about frequency wavelengths virtually irrelevant. Since dBM is a power measurement, that means for every +3dB difference, there is 2 times the power in transmission. So given the +80dBm difference in SAT radio compared to GPS signals, that comes out to be that Sat Radio signals are about 68 Million times stronger in transmission level than GPS signals.

The -130dBm level for GPS signals puts GPS signal strength down in the wireless broadcast noise floor range, and as I mentioned earlier, GPS signals were originally used for military use and were meant to be hidden signals, thus the reason they were buried into that noise floor, so they could not be detected by the enemy. That was not the original design intent of Sat radio signals, thus why the broadcast level is much higher for SAT radio signals as I originally mentioned.

So before you go on with more technical nonsense, do your homework.

Rednroll

Why don't you post us a vehicle drawing that shows this, since you're so sure. I originally came out and said, I'm not exactly sure where the combo antenna on the newer JK is mounted and so far the information you're posting isn't holding much water. So it would be nice to see something that actually supports the information you're posting.