Would two re radiating antennas in series work?

[jonasolof]

A year ago an iQue owner presented an interesting problem from the UK. Being a doctor, he also works with emergiencies. He would start from home in his own car, presumably from a garage. What would be the best way for him to use the iQue from the start, minimizing acquisition time and having a route from the start?

One thing we noticed is that if you shift from internal to external antenna, acquisition seems to start all over. Same thing if you electrically interrupt the connection to an external antenna.

I thought of his dilemma again and came to the following set up:

The iQue sits in its charger; active and with the internal antenna out. A rerad antenna might be needed to give it a signal in the office.

A phone call arrives, the user puts in the address and starts the routing while he rushes to the car.

In the car, there is a rerad antenna so that he doesn't have to interrupt acquisition by inserting an external antenna. So by the time he comes on the street, there should be a satellite fix and a ready route within the town with suroundings.

What if the car is in a garage? Would it be possible to have a rerad antenna transmitting to the iQue in the car, either directly through the windshield or via the car rerad antenna? In view of the remarkably good results (signal strength) reported in the discussions on the cF 1620 and a re rad antenna, one wonders if it would be possible to have one rerad antenna pick up the signal retransmitted from another, and still relay a useful signal to the Ique?

[donc13]

Originally posted by jonasolof
A year ago an iQue owner presented an interesting problem from the UK. Being a doctor, he also works with emergiencies. He would start from home in his own car, presumably from a garage. What would be the best way for him to use the iQue from the start, minimizing acquisition time and having a route from the start?

One thing we noticed is that if you shift from internal to external antenna, acquisition seems to start all over. Same thing if you electrically interrupt the connection to an external antenna.

I thought of his dilemma again and came to the following set up:

The iQue sits in its charger; active and with the internal antenna out. A rerad antenna might be needed to give it a signal in the office.

A phone call arrives, the user puts in the address and starts the routing while he rushes to the car.

In the car, there is a rerad antenna so that he doesn't have to interrupt acquisition by inserting an external antenna. So by the time he comes on the street, there should be a satellite fix and a ready route within the town with suroundings.

What if the car is in a garage? Would it be possible to have a rerad antenna transmitting to the iQue in the car, either directly through the windshield or via the car rerad antenna? In view of the remarkably good results (signal strength) reported in the discussions on the cF 1620 and a re rad antenna, one wonders if it would be possible to have one rerad antenna pick up the signal retransmitted from another, and still relay a useful signal to the Ique?

There's no need for that. The iQue is perfectly happy to create a route from "where you are" to where you are going without needing a satellite acquisition. It obviously needs to acquire the satellites to properly follow that route, but unless you're really doing something weird, you can drive the first few blocks "blind" by simply following the calculated route. After the acquisition, the iQue will give you prompts.

Re-radiating antenna provide a little, if any, improvement over no antenna itself. Add to that a 2nd one to re-readiate to the first and no, you will get no improvement.

The idea of a non-powered re-radiating antenna for GPS doing any good is a scam.


Don

[apersson850]

The antenna to antenna to antenna setup isn't even needed. If we assume the iQue is running it's GPS in the office, perhaps by receiving signals from a re-radiating antenna, where the receiving part is outside the window and the retransmitter near the iQue cradle, then the satellite ephimeris data will be current in the iQue. It must be, since it's computing the position of the desk, or rather of the receiving antenna, all the time.

If you then turn the iQue off, dash to the car, install it in the car, turn it on (including GPS) and drive out of the garage into the street, the time to acquire a new fix will be about five seconds. With all data current, and GPS startup already done while under the roof, that's all it takes.

However, if GPS hasn't been used for a while, it can't compute the position in less than about 35 seconds. That's physically impossible for the iQue, since it takes at least 30 seconds to download a current set of ephimeris data. Then that does also require that there is a good reception condition during these 30 seconds, or it will take longer than that. Ephimeris data is transmitted every tenth second, and is six seconds long. It takes three of these records, received in any order, to complete ephimeris data. You can easily see when it's done, since that's when the signal bar changes from hollow to filled.

[jonasolof]

Originally posted by donc13
There's no need for that. The iQue is perfectly happy to create a route from "where you are" to where you are going without needing a satellite acquisition. It obviously needs to acquire the satellites to properly follow that route, but unless you're really doing something weird, you can drive the first few blocks "blind" by simply following the calculated route. After the acquisition, the iQue will give you prompts.

Re-radiating antenna provide a little, if any, improvement over no antenna itself. Add to that a 2nd one to re-readiate to the first and no, you will get no improvement.

The idea of a non-powered re-radiating antenna for GPS doing any good is a scam.


Don

The routing part of was just to save time. I know it can be done without a fix. One of the doctor's concerns was to know which way he should go as he started is blue light journey so he would need a calculated route from the beginning and have the iQue be able to follow it.

The most important thing would be to have ephemeris data in as Anders pointed out. Starting acquisition as you come out can make it take a long time, since sat reception will be negatively affected by driving in an urban environment.

From driving through long tunnels, I've seen that the iQue will re-acquire a fix in 1-4 seconds even after satellite reception has been reported lost, so it is possible that a reradiating antenna wouldn't be needed until he's out in the street, even if it would take a minute or two to get goíng.

The idea of having a re rad antenna in the car is to avoid switching from the internal to the external antenna. In my experience, this will break acquisition worse than a temporary block of satellite signals.

I know there were non-amplified cell phone reradiating antennas and agree that such antennas are scams. However, the reradiaing antennas sold by Gilsson and manufactured by San José Navigation (http://www.sanav.com/re-radiating_antennas/re-radiating_antenna.htm)
use the ordinary linear two stage amplifier from a normal amplfied patch antenna such as the "Gilsson" and then uses a second small antenna for the output. Amplification is rated at 30 dB.
Judging from screenshots and posts, reradiation is as efficient as a direct cable connection. I don't believe it but intend to find out.
If one rerad antenna is efficient, two in cascade should work also.
I've ordered one RA-46 and one RA-45 on the hearsay that they work well just to see for myself. If they don't improve reception in a car I can always use them to have a GPS signal in the room where I work.

One reason why a re rad antenna could improve the ability to get and maintain a fix even if there isn't any net amplification would be a better view of the sky from the receveing antenna being on the roof.

[apersson850]

It's possible to change from internal antenna to extenal without interrupting the GPS position calculation. Simply don't fold the internal antenna until after connecting the external one. I've tried it. It works.

[jwc810]

Originally posted by jonasolof
Judging from screenshots and posts, reradiation is as efficient as a direct cable connection. I don't believe it but intend to find out.


the reradiating antenna should be able to transmit the exact signals it recieved from external antenna, maybe i mount the antenna on the roof of the car and it does make diffrence.

[jonasolof]

Originally posted by apersson850
It's possible to change from internal antenna to extenal without interrupting the GPS position calculation. Simply don't fold the internal antenna until after connecting the external one. I've tried it. It works.

IS there a cahce that holds current ephemeris data as long as the GPS engine is on in the iQue? That could be the reason for the long time it takes for reacquisition if I pull the external antenna while moving and then instert again. Had to do that sometimes to get the stylus.

Re the post above - "I want to believe" - It isn't clear under which circumstances and with what antenna arrangment the screenshot is done.

[apersson850]

But it holds that data even with GPS off. That's why it takes only 5-10 seconds to regain the position (well, for the rest of us, at least), if you recently had the iQue on.

[jonasolof]

OK, I'll do a more systematic test when the rerad antennas have arrived, also on down time effect.

[rwsmith123]

I think a bigger concern here is the reliability of the iQue. A reset because of an ESD when getting into the car etc. The other day I had to do a soft three times in a row to get it working again.

I think a better solution would be another gps alway on in the car and if needed a rerad ant if it's in the garage.

[jonasolof]

I haven't had a ESD reset in at least four months. And I always keep it in a pocket in a jacket without any case or other protection. The start up+insert antenna block has occurred a few times, but that wouldn't happen if it's already on.