Shortening active GPS antenna cable

[kuzm1nsk1]

Hi, would it be a good idea to shorten a GPS antenna cable or should I leave it as it is? Cable is 3 meters long but I only need no more than 10 cm. I found online some teardown pictures of an active GPS antenna and spotted probably a matching network right after the cable connection. So that tells me there is impedance matching and the cable can't be random length. Would this make a problem in terms of received power. Could I shorten it in some ratio so it would act like the original?

[vk4ffab]

Hi, would it be a good idea to shorten a GPS antenna cable or should I leave it as it is? Cable is 3 meters long but I only need no more than 10 cm. I found online some teardown pictures of an active GPS antenna and spotted probably a matching network right after the cable connection. So that tells me there is impedance matching and the cable can't be random length. Would this make a problem in terms of received power. Could I shorten it in some ratio so it would act like the original?

I do not see a problem with cutting it down, but I would ask, is it necessary. As long as the cable loss is not problematic for the application, i would not bother unless you need to reduce it for install neatness and cable management.

[fourfathom]

Hi, would it be a good idea to shorten a GPS antenna cable or should I leave it as it is? Cable is 3 meters long but I only need no more than 10 cm. I found online some teardown pictures of an active GPS antenna and spotted probably a matching network right after the cable connection. So that tells me there is impedance matching and the cable can't be random length. Would this make a problem in terms of received power. Could I shorten it in some ratio so it would act like the original?

I'm guessing here, but what looks like a matching network is probably a phantom power splitter.  At the receiver end of the cable there is a power injector that uses a capacitor and inductor to feed power down the cable to the preamp at the antenna puck.  A similar L/C circuit at the preamp splits off the power and couples in the signal.  This is a 50 Ohm system.

So, the cable is unlikely to be matched, and could be shortened if you truly need to.  I do know that this kind of antenna works well if you add a low-loss extension coax (using proper connectors and adaptors).  But your cable would need to be cut and very carefully spliced or (better yet) a new SMA connector attached.  This is GHz you are dealing with, so you can't be sloppy.  I wouldn't bother, just make a nice coil so the excess stays out of the way.

[kuzm1nsk1]

I’d like to mount it inside of a box so there isn’t much space for 3 meters of cable. I was planning to dissasemble the antenna case, desolder the cable, shorten it and solder it in the same way it was before. Well, I could buy one more antenna to make an experiment.

[wasedadoc]

As already postulated the coil and capacitor are just the separation of power and signal. Nothing about matching. No problem to shorten the cable as you propose.

[kuzm1nsk1]

I'll order a new one just in case and try it out. I should get one of those little VNA-s, they are so useful.