uBlox Antenna hacking

[Jack Crossfire]

So how is VCC_RF supposed to be connected to an active antenna on the uBlox NEO-4S? It only says "output voltage RF section". Can the coax on an active antenna be replaced with twisted pair or spliced by straightforward soldering?

[mlbco]

Jack,

Splicing the coax on an active GPS antenna must be done very carefully or you will end up building a GPS jammer! If you must splice, the key factor is to be sure the outer coax shield is intact after splicing. I usually fold back the outer shield on both sides of the splice and solder the inner conductor (heat shrink over the joint) and then unfold one side of the coax to overlap the other and solder around the perimeter to secure it. Cover the whole thing with more heat shrink. If you leave a significant portion of the inner conductor exposed without the shield, it will emit RF in the GPS band and jam GPS locally (like 3 ft radius). Of course, the unit will not acquire if this jamming occurs. I found this out the hard way by making a very sloppy splice and not keeping the shield continuous. I could hold a hand-held Garmin near the GPS antenna and the Garmin's received signal strength would drop off when moved close. Fixing the shield at the splice solved the problem. I recommend you don't even try twisted pairs!

Steve

[Jack Crossfire]

Sounds like anything which takes the GPS signal out of the antenna must be enclosed in a shield. An unshielded device like the Gumstix GPSStix can't be within several feet of the antenna.