Rick6a

Rick6a

Well Known Member
Is it okay to snip the two Garmin 496 antenna wires somewhere along their length so that the wires can be routed through the airframe via small grommets or snap bushings and then the antenna wires respliced/soldered back together again once the antenna wires are routed and the antennas themselves permanently affixed at chosen locations?

If it is okay, can the wires then be shortened as required or should the antenna wires remain the same length?
 
Let me start off by saying I don't own a 496... From what I've read, the two antennas are very different. The GPS antenna is a standard GPS antenna, but the XM antenna has a receiver built into it and interfaces to the 496 via USB.

I have cut GPS antenna cables for installation before, but you do not want to splice them like you would a normal wire. The only real way to do it is to cut the end off of the cable and then re-install a new BNC connector for the type cable that they used (usually RG-174). The frequency is just too high, and the signal strength too low to get away with a "wire splice".

For the XM antenna, I wouldn't recommend splicing the USB cable. While in theory it?s possible, since Garmin is the only manufacturer and it contains the whole XM receiver, I'd be worried about breaking something and then having to go through a lot of pain to get a replacement (or worse frying the 496 :( )

YMMV,

Paige
 
Just a gut feeling

After consulting with a well known RV avionics vendor who said it was okay to "cut & splice" the antenna wires and then considering Garmin's response to the exact same query that if I did snip the cables, the warranty would be voided, I faced a natural conundrum. Do I or don't I snip those wires? RV builders face dozens upon dozens of decisions over the course of a project and I tip my hat to those builders who partner in a project and still manage to get along with each other after years of sometimes difficult decision making. After all, feelings can't always be mutual!

In the end, I sort of took half measures. Via telephone conversation with Garmin support, I was assured both antennas would perform adequately in the environment under the cowl. Still, I decided not to mount the XM antenna after all, because, well frankly I dislike and refuse to commit/submit to monthly subscription services. Another reason I chose not to permanently mount the XM antenna is this minor factoid: I learned that it is the XM antenna itself that is activated and subject to fees, not the 496 unit itself. I figure I can always borrow someone else's XM antenna that has a paid subscription for the occasional flight when I want to access to real time weather and simply secure the borrowed antenna on the glare shield on those occasions. As for the GPS antenna itself, in the end I snipped the GPS antenna cable in two so I could mount its antenna under the cowl and route the cable through tiny snap bushings in the airframe back to the 496 itself. The antenna cable appears a tiny version of the ubiquitous RG58 antenna coax familiar to so many. The splice itself ain't pretty....I intertwined and soldered a good length of shielding on either side of the cable, isolated the resulting splice with heat shrink, then soldered the center conductor back together. After tidying up both splices by isolating and securing same, the moment of truth was at hand. When I turned the GPS unit on in my garage with the door closed, it took all of 15 seconds for the unit to acquire the satellites through the door and roof.

The bottom line is only you can make decisions for you. You pays your dues and you takes your chances.

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Decisions and the squeaky wheel..

....that gets the grease. Good deal, Rick. I bought a 3 month old 496 from a customer of mine after he bought a new Cirrus with the dual Avidyne screens and moving wx. He couldn't find the GPS antenna so I used an older cigar stub type antenna from my old Garmin 95 (the one that came off the Ark with Noah:D) until one day I had Garmin on the phone. I told the guy that I'd buy an antenna if they weren't $100. He then said, "Aw heck, what's your shipping address? I'll send you one":eek:...yes, I was very surprised and if you had messed up, you could always get another antenna.

Regards,
 
BNC Connectors

Rick,

I'm glad it worked out for you. A friend of mine tried the same thing and had horrible results; after I replaced the splice with a BNC connector, all was well. Some people don't realize that the antenna connector on a Gamin receiver is just a BNC connector with a plastic shroud.

BNC connectors for RG-174 (coax about half the diameter of RG-58) are available from a variety of suppliers:
Jameco RG-174 Clamp Type $5.85
Jameco RG-174 Crimp Type

Mouser RG-174 Crimp Type $1.90

DigiKey RG-174 Crimp Type $2.15

I included the clamp type which is more difficult to install because it doesn't require a special crimping tool.

Don't forget coax isn't just shielded wire. The cable is a transmission line designed for specific characteristic impedance (usually 50 ohms). Splicing it will disturb that impedance and will create losses. Just how much depends on the frequency of the signal, how long the splice is, and how well it matches the original geometry of the cable.
 
Successful splice experience here...

I've spliced a Garmin x96 portable antenna coax before, and it worked fine. I did keep the splice itself at the shortest length possible to still be able to solder the center conductor and have a piece of heatshrink in there to cover the soldered connection. I used a section of braided shield taken from a piece of RG-58 to cover the outside of the splice, and soldered that to the small coax's shields, and then put heatshrink over the whole splice joint. The splice stays hidden behind the panel, and the antenna still seems to work plenty good enough. I think shielding the splice helped control the signal loss to acceptable levels. Unless you're an artisan with a soldering iron, then attempting such a splice is probably not recommended. I've been soldering, and working with RF for over 40 years, so I kinda knew what I was doing.
 
FWIW, I cut and spliced mine, but only because I accidentally closed my tip-up canopy on the wire while installing it and it made a nice clean cut. Luckily the cut was just about in the right position. I put a new BNC connector on the now shortened wire and it's been working perfectly.
 
Cable length

When you cut and spliced the antenna cable did you maintain the cable length? Is this critical?
 
Rick6a said:
Is it okay to snip the two Garmin 496 antenna wires somewhere along their length so that the wires can be routed through the airframe via small grommets or snap bushings and then the antenna wires respliced/soldered back together again once the antenna wires are routed and the antennas themselves permanently affixed at chosen locations?

If it is okay, can the wires then be shortened as required or should the antenna wires remain the same length?
Click to expand...

I cut and spliced mine without problems--shortening the cable in the process. It worked well for many hours, but I was fairly careful with the splice.

I just put a gilsson aftermarket antenna in my wingtip and fished the wire into the cabin. I have tested the gilsson antennae with the Garmin and they work really well together. It helps that they are much cheaper than the OEM antenna and seem to work at least as well if not better. YMMV
 
I disassembled my 496's GPS antenna and de-soldered the coax from the PCB. I routed the coax and then soldered it back. It works perfectly. Signal strength seems to be the same as before. If you decide to do it this way be careful. It is very easy to mess up and ruin your antenna.
 
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