Internal antenna - Revisited

[tim adams]

On 5/11, I started a thread titled 'question about internal antenna'. At that time I was quite sure the internal antenna was totally dead and that I would need to get another rma from Garmin and send the unit back for repairs.

After posting the message, I did a hard reset and then went outside for 15-20 minutes and got no signals at all.

Frustrated, I left the unit in the cradle and did a couple of searches on the net for new, replacement units. I think that shows just how frustrated I've become. Then I returned to this forum and read a bunch of messages I hadn't read yet.

One caught my eye - it dealt with perhaps a unit had been given a new location and so it was taking longer to find a signal. While I hadn't changed anything, I did go to the gps screen and physically set my location.

I then retuned outside and in a minute or less, I had a faint, one satelite signal show up. While the unit never locked on, I knew that the antenna wasn't totally dead either.
The next day I took the unit shopping and while leaving home, it locked on (3 satelites) and stayed connected most of the time, only announcing it had lost the signal a couple of times.
Every time I checked it only had 3 satelites showing being seen.

This morning I again took a short trip and never lost the signal. When I got home I checked to see just how many satelites were showing and every signal one had a black bar under it! I've never seen that good a signal unless I was connected to an external antenna.

Why it's working now I don 't know but I'm a happy camper again, and the short moral of the story is - it appears that resetting my location may have solved my problem. IF you're having such a problem, you might be wise to do that also.

Tim

[apersson850]

Occasionally, it seems that my antenna have been dead as a doornail. By turning the iQue off, and back on, or sometimes by performing a soft reset, the antenna came back to its senses, and worked perfectly again. Or rather the software, interpreting the signals coming from the antenna, of course, since it's hardly the antenna itself that's reincarnated by a software reset.

[jonasolof]

There are more shades to this. What people call the internal antenna is in reality the amplifier circuits for the internal antenna, not the internal antenna itself which is just a piece of ceramics with a cupper lining on both sides. Or rather, that part of the GPS receiver which is activated as the internal antenna is folded out in contrast to the part of the receiver which is active when an external antenna is connected.

There are circuits in the receiver which have been shown to be vulnerable, to statics, to ageing or whatever. The situation has become better with new production (?), firmware upgrades.

Another weak spot was the switching circuitry to activate the GPS when the internal antenna was folded out.

Actually, "dead" antennas weren't totally dead. If you fed the GPS a strong signal (reradiating antenna) it would still yield a result, as shown on sat view. Only, the GPS was useless.

[apersson850]

That's also true. But when it appears completely dead, but after a power cycle, acts normally, then I'd say it's software only.

[PFflyer]

Several software related items can impact ability to lock on satellites.

Most common is incorrect time or initial location that sets off search for wrong group of satellites. Be careful if you use WorldMate, it can easily cause you to mistakenly screw up the unit's system time that the GPS process uses for initial search selection.

Based on previous stored info on satellites' orbital info, local time and approx location, the GPS unit picks the twelve most likely satellites to begin its correlation search.

Another stored piece of info is the unit's frequency offset centering to tune the Rx on center frequency. Along with this centering of Rx channel, unit calculates approximate Doppler freq shift offset for each of the twelve selected first search satellites based on where they should approximately be in the sky relative to your approximate location. Satellites closer to horizon have greater Doppler frequency shift (as much as 3 ppm relative to satellite directly overhead)

Closer to iQue particulars, the flip antenna is not the best, primarily due to not having sufficient ground plane behind patch antenna. Located close to the processor and its EMI emissions it likely suffers some interference from the digital noise generated by the unit. External mag mount antenna/amp on roof of car yields much better performance.

[apersson850]

Yes, very real and comprehensive summary of the situation. Still, this doesn't account for the bugs that may be buried in the software of the unit, bugs which may cause malfunctions to satellite acqusition, in spite of every other data being correct.