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G3X Touch GPS Antenna Length

Ezburton

Well Known Member
Patron
Hi all,

I am finishing up the install of a dual G3X Touch and go to the point of routing the GPS antenna which plugs into the back of the display (GA-26C). The cable for the antenna is about 10ft long and I need about 1ft.

Has anyone cut out the middle 9 feet and spliced it back together? I imagine the wires are pretty small and they and the shields would need to be soldered. I hate to have a big coil of wire hanging around behind the panel.

Thanks,
Don
 
Coax

Just cut to length and crimp on a new connector. Stein has the crimper and connectors and a video on how to install connector.
 
I would just coil it up, installing those mini coax connectors is "challenging".
 
I couldn't find anything about not cutting the antenna length in the install manual, just a lot about where to locate it (Section 22.1). Where did you see that?

I was thinking of reusing the mini coax connector... just cut the middle out of the cable and solder all the wires together and heat shrinking the whole thing.

Still not convinced this is an awful idea... but maybe it is something I can try after I get the plane put back together and back in the air.

Thanks
db

Garmin manual says to not cut the cable but coil it. Impedence issue
 
I don't think its a good idea to cut and re-solder. The impedance of the coax depends on have a continuous braid around the center conductor and the diameter of the center conductor. Both would have to be soldered and both would most likely be different than a unmodified section of coax. It would be nearly impossible to do and not effect the impedance. You will then create a discontinuity and the performance will be degraded.

As Bob mentioned the impedance isn't a function of the length of the cable. It has more to do with the relationship between the center conductor, the dielectric and the braid. However, the loss is a function of the length of the cable. I'm not sure if this is important or not in this application, only Garmin would know. If you were to shorten the cable it would be best to crimp on a new connector. With these smaller coax cables, and I haven't seen this specific cable this can be difficult to do correctly. I would suggest you just coil the coax as others have suggested since it will be hidden anyway.
 
I was thinking of reusing the mini coax connector... just cut the middle out of the cable and solder all the wires together and heat shrinking the whole thing.

Still not convinced this is an awful idea... but maybe it is something I can try after I get the plane put back together and back in the air.

Thanks
db

This is a horrible idea. Even good connectors introduce some loss.
Edit: see Ray’s post for a more thourough explanation.
 
Get a new BNC connector from Steinair and cut the cable. No need to have that much extra coiled up if you don't need it. I am not a wiz at electronics but had no problem installing the new connectors on my three G3X pucks I had mounted on a shelf under the cowling on my RV-10. My cheap coax crimper had the crimp die for it. I had no issues soldering the pins. https://www.youtube.com/watch?v=2-b1MAyk21o
 
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Garmin manual says to not cut the cable but coil it. Impedence issue

Cutting it won't change the impedance, but a poor crimp/solder will increase reflections, and a shorter cable will return more of them into the unit, increasing heat load. I'll venture a wild guess that the main concern here is with the longevity and reliability of the RF output electronics, not signal integrity.

Don't cut it; coil it.

EDIT: I just realized the OP was talking about the passive GPS *input* antenna, so the above is incorrect. Still applies to other RF cables so I'll leave it here for contemplation. ;)
 
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Hello everyone,
by no means is cutting the GPS antenna coax and simply splicing the cable back together a good idea, please do not do this without the proper tools or training to install a correct connector is only inviting degraded signal from the antenna.
The GPS antenna and extra coax length is designed so that the extra coax loss is of no concern when factoring system gains; if the coax is cut shorter and attempts to splice the connector end to this shorter cable end with solder and tape or shrink tubing then you're potentially reducing the 100% percent shielding effectiveness along with possibly creating an unknown impedance bump and possibly even a RF suckout that can result in acting like a notch filter all of which is unpredictable and could cause degraded operation of the system.

Please just coil it up and rig it in a safe fashion in the plane.
 
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