I was contemplating buying a re-radiating antenna today some of our vans have the reflective windscreens and i wanted something that would work with all my gps's regardless of connection..
A re-radiating GPS antenna receives the gps signals via an external antenna and uses another antenna inside the car to reradiate the gps signal (to any device) They cost around 30 pounds.
I got to thinking what one consisted of..
Active antenna
Power Source
Amplifier
Dipole (for retransmitting)
So I set about making one
I already had an active antenna - a cheap one from ebay (about 6 pounds iirc) and removed the mcx connector at the end. Bared off the coax.
I found in my box, an old usb lead and cut the 'B' end off. Bared off the wires and cut short and insulated the green and whte wires, leaving red and black. I connected the black (and the sheath) to the outer of the coax and the red to the inner. This was to supply 5v to the active antenna circuitry.
I then rooted around some more and fished out a capacitor (100 microfarad 16V) and attached one side to the red wire/co-ax inner. This is to isolate the DC from my intended re transmitting aerial.
GPS signals are around 1GHz. What else is around 1GHz ? mobile phones ! I pulled apart an old junk ericsson phone and pulled out the film antenna. Connected it to the other lead on the capacitor and held it against the back of the giz. The active antenna was thrown out of a window 5 metres away.
Immediately some signal (previously none as I was indoors). Wow definately doing 'something' i thought. My mind churned some more and i thought about using an antenna from a wifi router. Found one from my old siemens speedstream router. Held the capacitor leg against the inner of the socket. Within 20 seconds I had a good solid lock !!
Tried using a patch aerial out of a nokia 6210 and finally ended up settling on a stub aerial from an old ericsson.
Had to then build it into a box, any box. Hmm nothing lying about. except...
antenna (from 5y old ericsson phone)
internals
complete unit
Complete setup, active antenna on left, usb (for power) on the right - fed via a cigarette ligther to usb adaptor in the car.
about 20 secs after plugging the usb power in, 5m from the window
Would like to add a (very) small rf amplifier at some juncture (anyone know of anything simple that will work at around 1 - 1.5GHz ?) but its working well enough at this point to just use it.
Also would like to have the power and antenna removeable but couldnt find suitable plugs/sockets laying around (no maplin local )
comments / suggestions more than welcome
Social Networking Bookmarks