The Cessna 120-140 Association Forum

Where have others mounted their GPS antennas on a C120/C140? Looking for an inconspicuous location that works.

Inconspicuous? ...a challenge since it has to "see" the sats, as you're aware. In any event, this (pic) is where we put ours and it has worked flawlessly (since June '18). I'm confident that there's a better spot, 'though still difficult to camouflage. I did already have an antenna mount hole there from the old Loran C, so that helped my decision making. Victor recently completed his install...not sure where he or others have put theirs...will surely be interested where theirs and your choice to mount is, John. Mac

That is the area I am considering also Mac for the same reason, a beacon was mounted in that area that is no longer there. Definitely don't want to cut fresh holes in skin if I can help it. On the RV is was easy, they are inside the cowl. Fiberglass cowl allows this. Out of site and no drag.

Thought maybe someone had an epiphany with a clever place on their 140.

Joe Mancusi just mounted his forward of this position/twixt fore end of skylights @ the station where there was probably an antenna stand-off years past on his pristine 120. That still doesn't get anywhere near "hidden", of course, but it seems that anywhere in that area seems to function well. I do seem to recall a suggestion that the GPS antenna be kept a couple of feet from comm &/or ELT antennas FWIW. It's an emotional experience to drill holes of any size in these special old birds, isn't it? Mac

Put it inside the fabric wing. (Unless the wing is done in real silver...)

Caution:
IIRC Poly Spray dope uses aluminum pigment to shield the fabric from the UV rays which may attenuate the GPS signal.

What about on top of instrument panel inside just behind windshield? I operated with one in comparable location in my Bonanza for about 20 years with never a problem seeing the satellites.

I have two GPS antennas planned for my C140 project. A forward antenna on fuselage centerline for King KLN89B GPS and another Garmin GA 35 at the right rear roof for my Garmin GTX 335 ADS-B out transponder. Garmin recommends at least a 2 ft separation from other antenna to avoid cosite interference, which I was able to achieve with this pattern. Comm antenna is rear left of cabin roof top. Actual measured separations are 36 in between the left rear comm and right rear GPS, both of which are about 30 in from the front centerline GPS. FAA AC 43.13 2-B, para 306 recommends 36 in separation all antennas, but this is difficult to do in a C140 using the limited space in the cabin roof.

One thing I learned with the nutplates on the doublers to secure the antenna to the cabin roof is to use the Cadmium-plated type rather than the dry film lube type. This is because the antenna grounds are through the mounting screws (manufacturer recommended). The Cadmium-plated nutplates are decent conductors, but the dry film lubricant versions are not. I used Scotch Brite to remove the primer on the inside of my cabin roof and Alodined the area with 1132 Bonderite Pen to make a good ground plane to interface with the Alodined surface of the rectangular aluminum doubler. Bonderite 1132 is considered conductive when applied correctly in the right film thickness per DoD QPL. With this technique, there is no need to remove the paint or primer on the exterior of the cabin roof

I installed my GPS antenna directly aft of where Mac's is on the next fuselage bulkhead. I have a rather aft mounted com antenna so I needed to locate the GPS antenna aft to keep appropriate distance between the two antennas.

Coming out shortly is a full article on this subject in the next Newsletter.