APRS, GPS, and G/S antenna placement in wingtip

Hi All,

I'm thinking of using the following placement. Before I make things "permanent", I just want to be sure I'm not shooting myself in the foot. I've a couple of concerns/questions with regards to the picture below:

- I'm told that navigation signals are horizontally polarized. I'm just not sure if I should orient the G/S antenna (the 16" of stripped coax) front-to-back, side-to-side, or if a 45deg angle is good enough? I suspect side-to-side is best but due to wing-tip width constraints, I was thinking 45deg would be a good compromise.

- Is it Ok to make a "J" with the J-Pole antenna? (would that make it J^2?). It's a little difficult to see, but it follows along aft edge of the wing tip.

- And finally, is it Ok to have the APRS (144.390 MHz) and G/S (329.15 to 335 MHz) this close to each other? I think it's Ok since the G/S frequencies are no where close to any harmonics of APRS. But I am little hesitant about the proximity of the tip to the APRS antenna.

The GPS "puck" is going to be glued to the upper portion of the tip fairly far forward (similar in location where the DB9 connectors are positioned). I also plan on shortening the APRS' GPS and power leads considerably. The other wing-tip has an Archer NAV antenna and I'd like to keep that separate from anything else.



Thank you,

David_Nelson said:

Hi All,

I'm thinking of using the following placement. Before I make things "permanent", I just want to be sure I'm not shooting myself in the foot. I've a couple of concerns/questions with regards to the picture below:


Thank you,

Click to expand...

'Bout all you can do is try it and see if it works. We are learning as we go when it comes to stuffing wingtips full of antennae and transmitters. Let us know what you find.

scard said:

You've almost perfectly replicated my setup of aprs, jpole, G/S, lights, etc... in the same wingtip. Nothing is ideal, but mine works great, setup exactly as you describe.

Click to expand...

There ya go.

You've almost perfectly replicated my setup of aprs, jpole, G/S, lights, etc... in the same wingtip. Nothing is ideal, but mine works great, setup exactly as you describe.

Fantastic!

Thanks Scott! I've now got a good task list for tomorrow evening.

I did some reading up on the J-Pole and its radiation pattern. Just to be on the safe[r] side, I'm going to move the G/S antenna forward (just about under the GPS antenna) so it's not in the heart of the radiation pattern.

/\/elson

Hi David, FWIW, others have reported good performance with the coax glideslope antenna running down the gear leg. I installed mine here, since a run of RG-400 to the wingtip is quite heavy. This also largely eliminates concerns about APRS interference. I ran RG 316 to the wingtip for the APRS J-Pole, which is very light (this has been tested and works well). I believe that the glideslope signal is quite strong, so antenna placement may not be a huge factor in performance. Disclaimer: I'm not flying yet!

I did it a bit different . . .

I installed a Garmin 18X in my right wing tip using the mount for a magnometer. See photo. The Garmin 18X outputs RS232 and has a 50' length limit. I ran the RS232 from the wingtip to the bay behind my baggage compartment where I installed the RTG APRS unit. From there I have a very short run of coax to my modified bent whip antenna installed on the belly. System works great. A few minutes after the first time I switched it on i appeared on the aprs.fi site. I was amazed! The unit was pre configured prior to delivery.

MS19087 said:

I installed a Garmin 18X in my right wing tip using the mount for a magnometer. See photo. The Garmin 18X outputs RS232 and has a 50' length limit. I ran the RS232 from the wingtip to the bay behind my baggage compartment where I installed the RTG APRS unit. From there I have a very short run of coax to my modified bent whip antenna installed on the belly. System works great. A few minutes after the first time I switched it on i appeared on the aprs.fi site. I was amazed! The unit was pre configured prior to delivery.

Click to expand...

Mark, good to hear your tracker is working nicely! The whip is the way to go for max performance.

I am curious, however, as to why you went to the trouble to mount the GPS all the way out on the wing tip. Why not put it somewhere in the baggage compartment near the tracker?

Good question . . .

I wanted a dedicated GPS for this 'experiment' as well as wanting to isolate the entire APRS system. If I ran into RFI issues with the unit I wanted the ability to turn it off without effecting my other systems. Also I did not want to mount a GPS antenna in the baggage area. This one is tucked away and only required running the RS232 from the wing with my other cabling. I think I will have great coverage with my bent whip which has a very short RF run from the RTG. I did a bit of military aircraft antenna work years ago and have some strong feelings on antenna mounting locations, grounding and RFI.

Hi Noah,

I'll keep in that in mind for "plan b" if this causes too many problems.

Tracker Monitoring?

I've been playing with a Byonics APRS tracker (in the Citabria I fly these days), and intend to install an MT-RTG in my under-construction RV-7. One of the concerns ... potentially misplaced ... is adequately monitoring the APRS transmitter during its operation. With the MT-RTG mounted in the wingtip it would be impossible to monitor its operation, and therefore impossible to disable it if it decides to misbehave.

That said, I realize that folks launch these things in high altitude balloons and clearly -those- can't be monitored either. So my question comes down to, is there any concern about the unmonitored nature of these remote installations?

I'm looking forward to being convinced I'm concerned about nothing.

DwightFrye said:

I've been playing with a Byonics APRS tracker (in the Citabria I fly these days), and intend to install an MT-RTG in my under-construction RV-7. One of the concerns ... potentially misplaced ... is adequately monitoring the APRS transmitter during its operation. With the MT-RTG mounted in the wingtip it would be impossible to monitor its operation, and therefore impossible to disable it if it decides to misbehave.

That said, I realize that folks launch these things in high altitude balloons and clearly -those- can't be monitored either. So my question comes down to, is there any concern about the unmonitored nature of these remote installations?

I'm looking forward to being convinced I'm concerned about nothing.

Click to expand...

You're concerned about nothing.

Excellent!

I have the APRS on its own circuit and a switch on the panel. While it is mounted on the wing, I cannot "monitor" it but if I suspect problems, I can turn it off. Also, the switch is handy for those "stealth" missions!

More Antenna Questions...

I have several questions about the 300 ohm twin-lead install. These questions fall into the category of a little bit of knowledge has made me dangerous. I have the M-T FA Tracker and plan to install it in the wingtip of the -8.

Does the antenna need a ground plane to the aircraft structure?

With the antenna being end fed, are there any RF interference concerns or RF hot spots coming off the antenna?

What are your thoughts about using commercial grade velcro to mount the antenna and transmitter in the wing tip?

I plan to tap my power source off of the wing tip nav lights. I think I will continue to power the unit through the supplied cigarette adapter. I like the idea of having the built-in fuse in the cigarette adapter as part of the circuit and located close to the source of power from the nav lights.

At least the way I understand the present antenna configuration, with the antenna attached to the transmitter, the only path to ground is back through the B- power supply lead via the transmitter unit. If so, I would assume this is not an ideal pathway back to ground. Should I be concerned about this?

Thanks,

DAGO said:

I have several questions about the 300 ohm twin-lead install. These questions fall into the category of a little bit of knowledge has made me dangerous. I have the M-T FA Tracker and plan to install it in the wingtip of the -8.

Does the antenna need a ground plane to the aircraft structure?

Click to expand...

No. That is the reason for using a J-pole, no ground plane needed.

With the antenna being end fed, are there any RF interference concerns or RF hot spots coming off the antenna?

Click to expand...

This has not been a problem. There might be a unique installation that would create some RFI issues (J-pole adjacent to NAV antenna?) but generally speaking you won't need to worry about this.

What are your thoughts about using commercial grade velcro to mount the antenna and transmitter in the wing tip?

Click to expand...

That will work fine. Good duct tape is even easier to use.

I plan to tap my power source off of the wing tip nav lights. I think I will continue to power the unit through the supplied cigarette adapter. I like the idea of having the built-in fuse in the cigarette adapter as part of the circuit and located close to the source of power from the nav lights.

Click to expand...

You can do that, the only concern I would have with using the cig plug in a remote location is the possibility of it working loose. I would prefer an in-line fuse if you want fuse protection. I've forgotten the voltage required for the FA, make sure it is 12v if you ditch the plug. Some plugs drop the voltage to 5vdc.

At least the way I understand the present antenna configuration, with the antenna attached to the transmitter, the only path to ground is back through the B- power supply lead via the transmitter unit. If so, I would assume this is not an ideal pathway back to ground. Should I be concerned about this?

Thanks,

Click to expand...

No.

Happy tracking!

Thanks...

Thanks Sam! Won't get the unit installed in the -8 until September. For the time being, I have it installed in the car.