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 Team Rocket F1   AVIONICS    Page       Last Modified: Thursday, 07-Feb-2008 10:04:38 EST

** The Plasma III electronic ignition is installed behind and on top of the EFIS, but I cover that topic in the engine section.

Dual Horizon 1 EFIS and EIS

I ordered my Grand Rapids Technology Horizon 1 dual screen single AHRS system with integrated Engine Information System at Oshkosh 2005. I delayed the order in November when Sandy called me and told me it was finally ready to assemble and ship. At OSH I told them I wouldn't be ready for at least two months, so the delay was mine. I'm sure they didn't mind the delay with all the OSH orders they got.

Besides the dual screen option, I also ordered the fuel flow monitoring, the ARINC 129  interface (for the Garmin 480) as well as the internal WAAS GPS. I wanted all the bells and whistles.


When the order came (18 pounds), I was surprised at how much stuff there was. I laid it out on the kitchen table. It looked like a daunting pile of bags wires and papers. I looked at the installation instructions and began to read them. I thought to myself "these instructions are of little help". I had read them through on the GRT website a couple times. With the parts in my hands, I just didn't get it. Then the light turned on when I saw a cable wiring instruction manual. Duh, it was separate from the installation instructions. I hadn't seen that before, and it turned out to be the key to getting this project started.

The manual isn't exactly cookbook, but so far it seems to be fairly complete. I had a hard time figuring out which monitor was DU (Display Unit 1) and which was DU2. Finally, after reading the wire code layout, one of the 3 factory pre-wired, interlinked 25 pin cables has a brown wire on it. Guess it's up to me which monitor to call DU(1), but it makes a difference on the wiring. The DU(1) is the unit you HAVE to use to setup some parameters in the system once you get it up and running.

I was anxious to at least test run the units (Boys and Toys, you know...), so I set the DUs in my panel. A perfect fit. And I set the  AHRS on my avionics center shelf. I had that located perfectly as well. I had also determined that the bottom monitor (DU) would just clear the shelf due to the cant of the instrument panel. That was just right, and I was glad that I had my instrument panel extended 1 inch at the bottom. So far, so good.

I took the rats nest of the main cable (3 -  25 pin connectors with up to 20 feet of many, MANY color coded wires) and laid it out on the table. I displaced the unconnected wires, bundled and marked them, and set them aside. I took a tape measure and approximated the distance between all the pin connectors at the back of the DU's and aft side of the AHRS with the units sitting in my instrument panel. Then I cut the yellow and brown wires. My DU's and AHRS are only about 8 inches apart, and I think there was at LEAST 2 (if not 4) feet of wire pinned for those connections. I wanted to reduce the amount of excess wire, so I cut, stripped and crimped new female pins on the DU pin connectors. I set the cables in place on the units (just resting in my panel). I liked the result!

The manual tells you that although the units are internally fused, you still should use circuit protection. I'm still trying to decide whether to have 3 power sources to each unit, and whether to use blade fuses, circuit breakers, or just use fusible links on the wires. I'm leaning toward the latter. In the mean time, I wanted to power up the units to see what they looked like. I stripped the 3 red and 3 black wires that  power and ground each of the units and just used some alligator clips and a fuse block I had laying around with a 5 amp fuse in it, and clipped the EFIS wires to my main bus. A flip of the master... and.... SUCCESS!


PRETTY COOL!!  I gave the units time to do their checkouts, pressed the ACCEPT buttons and checked out the color screens. Oh yes, these are going to be sweet.  The color in the pics look crappy, and don't give you a real idea of how nice they looked in the panel. Also, the protection film is still on, and it makes the colors a bit darker than they really are. I'm in no hurry to remove the film, but I was still impressed.

Let the real wiring BEGIN!

Wiring Notes:

The AHRS doesn't need OAT, but the EIS does. So if you have a Horizon 1 and EIS, run one of the OAT probe wires to a splice into the gray wire of the EIS. Remove the gray wire from the AHRS cable. The other OAT can go to about any ground, preferably close to the unit. Mine went to the E-bus ground.

The EFIS has 3 power inputs for the 3 units (AHRS, 2xDU). I have a dual battery system, so rather than have separate wiring to each battery with a switch, I chose to have dual wiring to the E-bus and a 5 amp fuse. IOW, I crimp spliced the three power wires to the unit and ran a single 18 AWG wire to the bus. Times two. If the primary fuse blows, or I have to switch to secondary power, I have two independent sources of power. I may end up putting a remote switch and a direct to battery spliced line in to the backup battery for a 3rd source of power. But I can't imagine that I would ever need a 3rd source of power. I may end up putting a 3rd battery up on the avionics shelf, and a remote switch, just in case I blow my whole electrical system (extremely unlikely). For now, KISS.

When the master switch is on, the EFIS is on, even during engine start. This may be hard on the units, but it's easier to contend with. I want it all turned on at the beginning. I want to look at the display units before engine start. Later on, I may re-configure the wiring to cut out the display power so that they shut off when the engine is cranking.

The EIS has a green/black wire that you splice to the DUs. The single serial out of the EIS goes to a single serial in on each of the DUs and can be a simple splice 1 into 2.

EIS (Engine Information System)

The EIS may not strictly be avionics, and probably should be covered somewhere else. But my Grand Rapids Technology EIS is directly linked to not only a bunch of engine components, but is really visualized by the EFIS. The EIS is the 6000 model for 6 cylinder engines. GRT still ships the original unit, and I suppose you could actually put it in your instrument panel, as builders have been doing for years. But I think the faceplate looks like shit, and there are so many pages with so little information, I chose to just hide the unit under the boot cowl, behind the instrument panel.

I fabricated a center avionics shelf that I screwed to the back of the instrument panel,
and it is also screwed to the stainless firewall. It is level with the three axes of the ship . The main reason to build this shelf was to have a place directly behind the EFIS Display Units (DUs) to mount the AHRS. The AHRS is the guidance system and brains of the EFIS system. I also plan to mount the Plasma III electronic ignition modules on a separate self  mounted over the top of the AHRS on the center avionics shelf. This was also a good place to mount the EIS unit.


The instructions that come with the EFIS and the EIS are definitely not cookbook. They appear to be fairly complete, but still leave a few details to the imagination.  Where the EFIS has locations for 3 power inputs (but only one ground), the EIS only has one power input. And you can use up to a 5 amp fuse. After mounting the EIS unit to the pair of .025 formed brackets on the Plasma EI shelf, I gathered up the 2 EIS cables and figured out what each one was. The EGT/CHT cable is pretty easy to figure out. The wires are twisted pairs, 6 each for the EGT and for the CHT. They are inserted into the 25 pin connector in numerical order, so each twisted pair corresponds to each cylinder in order, and is also displayed for each cylinder in order on the monitor.  I separated the wires and labeled the pairs, and put some shrink tube over the bundle at the EIS pin connection.

The other 25 pin connection cable is a little tougher to work with. Each wire is a different milspec wire color, so that makes it easy. But all the instructions give you is a diagram and suggestion as to what each wire connects to. In my case, there are 6 aux inputs, and I will probably use them all... as long as the input voltage doesn't exceed 5 volts. Well, that screws up a second battery voltage monitor.  Most of the wires from this cable are going back to the engine compartment.  

I decided to separate the power and ground wires (red and black... how easy is that!?!) from the EIS and run them to the E-bus with the AHRS and DU power and ground wires. I used a bit of plastic conduit and zip tied it to the bottom of the instrument panel under the avionics stack. Then the wires loop over behind the keyed ignition and then down the right sidewall through the #2 bulkhead to the E-bus. There, the power wire works off a 5 amp fuse (the smallest smart glow size) and the ground wire is attached to the E-ground bus there, too.

There is no switch for the EIS unit. When the master is on, the EIS (and the EFIS) comes on. That way, you can monitor your engine and fuel status from the get go. When the master comes on, the LED readout of the EIS instantly turns on, self checks and displays the first page of information. The unit has pages and pages of parameters that are all changeable and configurable for many variables. That task looks daunting and I don't even have the thing connected to any components yet.

The first glitch was how to attach the serial output from the EIS to the DUs of the EFIS. Well, the EIS has one green/black wire, and the DUs EACH have a green black wire. Seems simple enough. Guess I'll get a splice connector, shorten the wires and run the one EIS output direct to the two DUs.  I went ahead and emailed GRT before cutting any wires and asked just to be sure I wasn't missing anything.

Next confusing part was the OAT temperature sensor. Seems the EIS, the AHRS  AND each of the DUs have input for this, too. The OAT sensor only has two wires. Time to email GRT for recommendations on that one, too. The OAT sensor has to have some kind of power to it...

Wiring notes:

The OAT probe gets wired to the gray wire on the EIS, not the AHRS. Then the EIS tells the DUs what to display through it's serial connection. The AHRS does not need OAT input, so just skip wiring the OAT to the AHRS (unless you don't have the EIS).

The green/black wire of the EIS can be spliced to the same of the DUs. The serial out of the EIS goes to the G/B serial in of the DUs. Crimp a simple 1 into 2 spice.

I ran the single power and the single ground wires of my EIS to the E-bus. When the master is on, the EIS is on. 5 amp fuse.

GRT Magnetometer

The GRT instructions for the magnetometer are pretty complete and straight forward. Essentially, you want to keep that little black box away from anything electrical or magnetic. So you want to try to keep it 18 inches from ferrous metal and power lines, as well as a good 5 feet from antennas.  Also, it has to mount within .5 degrees of the AHRS. Well, I went to a lot of trouble to level the AHRS with the ship so that it might make locating the magnetometer a little easier. I have the EVO wings, and have NO idea where I could locate the thing. I decided to put it back in the empennage. That has some drawbacks: it actually is close to about 6 AN3 bolts and nutplates, and if the thing needs serviced, more than likely I'll have to remove the vertical stabilizer.  However, the nice thing about putting the magnetometer in the location I used is that it is automatically level with the ship (except for the twist inherent in the factory fuselage).

MagnatometerBracketed.JPGThe location I used for mounting the magnetometer is just forward of the aft turtledeck bulkhead. It's just inside the big hole in front of where the vertical stab mounts to the tail. I used a 3/4 x 3/4 formed angle to make the front bracket. It sits on top of the longeron from side to side. The angle ended up a little over 9 inches long. I beveled the ends so that it sat flush and snug against the skin. I went ahead and used #6 stainless screws and nyloc nuts to install it. I measured the exact middle of the bracket and drilled a hole for a #10 screw so that the middle of the magnetometer would sit centered in it's forward bracket. I made another bracket out of another formed angle of .032, but this one was about 3 inches wide. I made it just small enough to fit through the inspection hole at the aft end of the turtledeck. This bracket is not that much narrower than the front angle bracket. I also used a pair of #6 stainless screws and nyloc nuts to fasten that bracket to the tops of the longerons. I wanted to rivet the brackets in place, but there was just no way I could get in there. As it was it took me almost 3 hours to make these brackets. WHEW!

I measured the middle of the aft bracket as it sat snug between the turtledeck skins. I drilled for another #10 mounting screw on the bracket to sit the magnetometer smack dab in the middle of the plane. Since both mounting holes are centered and the brackets sit on the longerons used to level the ship, no further physical leveling of the magnetometer is required. Well, that's my story, and I'm sticking to it. Later on, I'll have to go through the adjustment program in the EFIS to get it all set up properly. Probably will have to allow for some interference from nuts and bolts in the area. Otherwise, this thing is out of the way of most everything electronic and ferrous!  

Don't worry if the magnetometer in the picture looks offset a little. The cameraman was not quite centered, and neither is the label with the arrow on it. You'd think that if GRT though getting this thing set up properly was THAT critical, at least they'd put the ARROW on STRAIGHT.  

Note that my angles sit with the web upwards. IOW, they sit completely on top of the longerons and go upward from there. I had to bevel the web a bit to allow for the converging curvature of the turtledeck. Also, note that I had to make a rather large and deep notch in the bracket to allow for a pin connector to screw on the back of the magnetometer. Yes, that weakens the bracket a bit. The magnetometer, however, is about as light as a feather. The drag from the cable would probably weigh more than the unit itself, so I think the two  formed .032 angle brackets are more than sufficient to support the magnetometer.

Now to wire it up... I ran the 6 wire cables from the AHRS down the right side of the instrument panel and then around the battery to the forward stick bay. Here the 6 wire bundle will have to penetrate the wing spars though the carry through. Then I ran the magnetometer wires along the right side inner wall. I swapped the wires to the left side of the ship under the baggage floor, using a piece of 1/2 inch conduit under the elevator push tube. I then ran the bundle through the existing conduit to the tail end of the turtle deck. A couple of the pins broke en route, and the wires weren't the same length, so I cut them and crimped all new pins. A little shrink wrap and then screwed together the connector housing, some zip ties to restrict the wires away from the push tube and cables and it's time for a test run.

BTW, the instructions from GRT say to use brass or nylon for mounting the magnetometer. I bought a couple  #10 screws and nuts in each material and found that both of them were not sturdy enough for my tastes. The brass was too soft without locking washers ( could have used thread locker, I guess) and the  nylon would not stay tightened and the nut wanted to jump threads on the screw. So I just used non-magnetic stainless steel. Hope it works OK.

I powered up the EFIS and found that the horizon and ball and slip indicator were slightly off. Hmmm... guess the fuselage IS leaning to the left and bit, with the tail sitting a bit wonky.  IOW, the artificial horizon seems to be working properly.

When I was ready to start the engine and taxi test, I noticed that the EFIS showed a slight left turn and the ball was off to the right in the slip indicator. I did a pretty good job getting the AHRS aligned with the magnetometer, but I had to shim the AHRS with ONE washer under the #6 screws. I put it under the front right corner. That was enough to level the horizon and bring the ball in between the center marks. In order to center the ball farther, I just racked the shelf that the AHRS sits on. Just a squeeze of the aluminum was all it took. Now at rest, the ball is centered and the horizon is level. Better make sure your tire pressures are even and that you are on a level floor. If the fuselage isn't level, there's no point in leveling the EFIS. And then that can change once you get in flight, too.

Interestingly, the EFIS raw data showed the fuselage to be .3 degrees wing down, and 11 degrees tail down.  I need to level the tail and double check the EFIS settings for level on the horizon. Or just check the "waterline" on the plane to make sure it shows 11 degrees tail down. Then it will be interesting to check that data in flight.

EFIS Upgrade: Memory, Hardware and Software

Fall 2006 I was working in the cabin installing plumbing for the fuel system. I decided to sit in the cabin and make airplane noises. While playing with the EFIS, I noticed that it had last year's software, so I decided to try to update it. That's actually pretty easy.

When I first was looking at the GRT Horizon I, I thought I would have to get a laptop and take it in the plane with me to update any software. Not the case at all. There are USB ports in the back of the units for input and output. I saw that GRT had system software updates. It was just a matter of copying the software from GRT's website onto a USB memory stick, plugging it into the back of each unit, and then going through the menus looking for update prompts. It was pretty painless.

PCAdapter.jpgCompactflash_.jpgThe GRT Horizon I EFIS units are somewhat like large PDA's. They run on Windows CE. They do have an accommodation on the motherboard to accept a Type I pc adapter and a compact flash memory card. GRT will tell you that they have only tried a 32 MB cf card, but that it is likely that a 2 GB card will work. At this point in time, I didn't feel like spending $100 for 2+ gig cards, but found 1 GB cards for under $30. 1 gigabyte has room for a LOT of software.

I opened the units (13 screws to remove the case) and simply pressed the adapter to position. It can only go in one way. Easy. Then I pressed the cf card to place and closed the case.

The EFIS software system didn't seem to recognize that I had preloaded the memory cards with all the upgrade software. The unit still prompted me to load the software from the USB port. So I re-copied the upgrade software to a 256 MB USB memory stick and used that in the USB port.

The GRT system now has detailed terrain data for the entire world available for installation into the EFIS. I had to first update the system software (via USB memory stick).  Supposedly, there's not enough free memory in the stock DUs,. so you are prompted by GRT to add memory to each of the units to store the terrain data. I wouldn't be surprised if the memory upgrade can be used for more than just terrain data in the future. The website has instructions on what and how to install for memory upgrades.

I had preloaded all the most recent software from GRT onto the compact flash memory card, but the units didn't seem to recognize it. I finally ended up copying the TERRAIN_NW.DAT file onto my USB memory stick, and then changing the file name to TERRAIN.DAT . GRT's release notes say that this isn't necessary, but that's what it took to get the EFIS system to upgrade/input the software. Finally, I got the "operation complete" message on the EFIS screen. Now I have terrain data in each DU for all of North America, not just the US, which is the "default".

Garmin Stack

Garmin GMA 340The top of the stack is a Garmin GMA 340 audio panel. I do fly IFR, so I wanted the marker beacon and other features of the audio panel tying all the radios together.

Garmin GNS 480NOTE: The GNS 480 has been discontinued by Garmin. Although the  SWEAR that they will continue to support this box for a long time, my experience with other Garmin products has been otherwise.

The key radio in my stack is the Garmin GNS 480. That is actually a Garmin AT. It has been WAAS enabled for years, where the 430W and 530W just came on line earlier this year. I figure that with 4 or more years in service, the 480 is probably the way to go. It operates like a flight director. That doesn't mean much to me, but evidently those that "fly the line" in the big iron seem to think this is the way to go. At least the general format/function is familiar to them (not me).

The 480 is a finicky bitch. You have to make sure there's nothing getting between the bezel and the "tube" (tray to the rest of the world). Make sure your panel opening lets the faceplate contact the tray in order to seat the pins at the back.... which have to be within a .020 tolerance.

The configuration of this box took quite a while. The RS232 serial ports have a myriad of combinations and are interdependant. I finally go the box configured and working, but it was a LOT more trouble that I would have thought.

Garmin AT SL30The "backup" or "secondary" nav/com is the Garmin AT  SL30. I really didn't need another GPS, both the 480 and the GRT EFIS have WAAS enabled GPSs in them. However, I did want a solid back up com and nav with a glide slope. The Garmin AT SL-30 and SL-40 (no NAV) radios have some great features and are very reliable.

Garmin GTX 327The transponder is a Garmin GTX 327. Nothing fancy here (although it is solid state and "digital"). I didn't opt for the traffic and whatnot on the more expensive models, I just didn't think it necessary with my type of flying.

With my GNS 480 driving this transponder, the RS232 settings on the transponder "Channel 1" are "REMOTE" and "REMOTE".  The 480 serial port used for the GTX series is #6 and set as GTX32 and 9600 baud.

Fall of 2007 I finally had a rolling chassis in my hangar. Time to cough up the dough and get some radios. I stuck to my original plans and ordered a Garmin stack from Start Avionics in Georgia. They asked for a check for the full amount in advance, and 3 weeks after they get (clear?) the check, they will wire up the radios (and the TruTrak Digiflight II) and ship it to me.

I ordered my Garmin Stack from Stark Avionics. They are a full service avionics shop down near Columbus, Georgia. They sell pre-wired stacks to lots of experimental builders. Being that they are a certified shop, and the radios are pre-wired, supposedly Garmin will validate a warranty. Anyway, with a couple phone calls a few emails and lots of money, my stack finally got into the assembly line. Once the check clears, they start. Or you can pay by credit card for a 3% up charge. Understandable since Stark sells their avionics for such a low price. Guess they just want to make sure that their techies at the benches stay busy, and probably make most of their money on their published "pre-wire" fees. Works for me.

I'm typing this paragraph as I sit here waiting for UPS to deliver my radios. I have no idea just how pre-wired the radios are. I know that they can't have everything pre-wired, since my EFIS and autopilot are already in the airplane. Hopefully, since I have the RadioRax mounting rails already installed in the panel, it won't take a whole lot of work to wire the radios into the system. Lessee, 4 powers, 4 grounds, maybe about 10 more wires between the radios. Then there's the headset jacks... which are also supposed to be "pre-wired". I've got this feeling that locating those is going to be the biggest job of this little exercise.  Now where is that UPS driver???

Well, the UPS guy showed up with 30 pounds of avionics thrown over his shoulder and promptly dropped the box to the floor. Unlike some boxes that say "FRAGILE, HIGH DOLLAR AIRCRAFT PARTS", this box said nothing except "return if seal broken". I guess they'd rather not let people know there's 20 grand worth of avionics coming out of that shop (probably day in, and day out). A little FRAGILE note here and there might have helped a little.

Here's what was in the top of the box:

My "wire count" was off the mark by about a factor of TEN!  HOLY COW!  Man, that looks like a lot of work. Much to my happiness, each and every wire and coax is labeled. No instructions, per se, but I'm sure the install manuals might help a little. Otherwise, just gonna be lots of crimping and lots of soldering. I think this may take me more than a couple nights....

AvionicsTrays.JPGOf course I ran out to the airport with my new toys and started right to work. First thing was to put the nuts in the RadioRax rails. That was an hour job. Then it was time to mount the trays. My radio expert Jeff Tucker suggested making a "story pole" in order to mark the rails for the approximate position of the nuts. That worked out great. The first tray in was at the bottom, the transponder. That tray actually lips out over the instrument panel. Then the rest of the Garmin trays go in just as I listed above. The Garmin trays are nicer than the GarminAT trays, but none of them required any special fittings. Just put 4 screws at the front of each tray, that's all you need.

It's nice to have friends willing to help, especially if they have mad skills and nice tools. Jeff just happened to stop by at the perfect time with the right tools. He had an extension Phillips screwdriver that made this job easier. You need to get #1 screws in the back of the trays, about a foot from the front. And the handle has to be REALLY small, especially inside that SL-30 tray.

Jeff organized the wiring harness. Each bundle of wire and BNC (female) connectors had to be screwed to the back of the trays. The Garmin tray backs have the screws already in them and drop into slots. All you have to do is tighten the screws. On the Garmin AT tray you have to put the screw on the driver, then try not to drop them all the way to the back corners of the trays. That was fun.

AvionicsWiringMess1.JPGThis is what it looks like with the tray backs in place and the bare wires ready to be located and ran to their respective positions. What a MESS!

The nice thing is that I have room behind the avionics, believe it or not. Going to have to make some tight turns, and working with the 25 pin Dsubs behind the EFIS screens is going to be tough.

As big as a mess as the pic to the left appears to be, Stark Avionics labeled EVERY wire and coax. They also bundled everything that goes to each different unit. For a big spaghetti mess, it's actually quite organized. And it was worth the money to get the avionics all pre-wired!

AvionicsTestFit.JPGJust what the doctor ordered!  Had to test fit the boxes just to make sure they all went to seat, not only in the trays, but in the business end at the back of the trays where all the connections are.

Yeah, yeah, yeah... a lot of guys like their radios on the left.  Every plane I've owned, however, has the radios on the right. That's what I'm used to, that's what I did. Guess it's not the "fighter" style set up, but what the heck. It will work for me.

I organized the already organized cables, basically pointing them the direction they needed to go. Certainly most go to the EFIS. I bundled the power/ground wires and moved them toward the aux/avionics bus. Decided to run the headphone jacks on the right side, too.

First thing after getting the boxes in the tray and laying out the wires was to run the powers and grounds to the avionics bus. I bundled the wires all together, then separated the blacks from the whites. I drilled a new hole in the bulkhead just in front of the Blue Sea fuse block, inserted a grommet and proceeded to insert the wires. I noted that my "bus" had 12 slots, but 16 wires. Hmmm.... not good. I reorganized some of the less critical wires and piggybacked them onto other wires. Not a great idea, but it'll work in the short haul. In the end, I may run a couple of those wires to another auxiliary bus or the battery (hot all the time) bus. For now, I just want everything running.

The two radios actually need 2 fuses each. The Nav side is separate from the Com side. So I had 6 power wires to run, terminate and fuse. Stark labeled each power wire with the appropriate sized fuse, which made hooking them up pretty easy. I had that information already, so it was nice to have confirmation of my research on the amperage. The ground wires were not marked, but I didn't care. I terminated each wire with a crimped ring and put them on the ground side of the bus.

The transponder, SL-30, and audio panel lit right up. The GNS-480 was another story. It wouldn't power up. After lots of unsuccessful research, I finally put a multimeter on the backside of the 37 pin plug on the 480. A good hard push showed current to the #16 pin, and the unit lit up. AHA! Bad pin in the connector. Nope. Turns out that the radio wasn't going into the tray enough. We loosened the screws on the RadioRax and held the tray as far forward as possible and tightened it down. After that, good steady power, even with some serious wiggling on ALL of the connectors.

I was confused about the markings on many of the wires from the 480 to the EFIS. They were labeled A, B and C plugs. Huh?  I knew the A plug was used on the EFIS MFDs, but thought the B plug was "for future enhancement" (not used). And what the heck is the "C" plug?  Tony at Stark set me straight, the B plug is in fact used, and the C plug is the 9 pin serial to the ARINC 429 module.  Ok, now to crimp some 30+ pins so the boxes can talk to each other.

Another fly in the ointment was the GPS antenna supplied with the GNS480. That has a TNC connector on it's base. Bummer. A TNC terminal for RG400 cable is $40 plus shipping. Screw that. I'm getting an adapter for about $5. I need a TNC male to BNC female adapter, and they have them at the local Electronics Depot.

I asked Tony at Stark Avionics about using the adapter on the GPS antenna. He gave me a short lesson in coax and connectors:

You have an estimated .2 db worth of signal loss for each connector break.  So adding one more connector shouldn’t hurt you.  RG-400 or 142 should be the coax you are installing for the GPS antenna.  The install manual calls out for no more than 7db total signal loss between the antenna and the GPS receiver.  Figure on .18 to .20 db worth of loss for each foot of RG-400 or 142 you have and include .2 db for each connector.  As long as you come under a total of 7db, you should be fine.

I probably need to make an immediate 90 degree turn from the TNC adapter to the RG400 cable. Lessee.... 1 break at the radio, 1 break at the tray pigtail, 1 break at the 90 degree adapter, 1 break at the TNC adapter, and 1 break at the antenna for a total of 5 breaks. And two feet of coax.  Total estimated db signal loss is 1.4, which is well under the 7 db max loss. Sweet!

Once the antenna coax was all connected, the last thing to do was run the two cables for mics and phones. These shielded cables were already bundled and marked, nicely done and beautifully arranged.  The labels on the wires that solder to the jacks wasn't familiar to me. I started looking for a GMA 340 install guide and there wasn't one. There were a couple on the internet, but they were old and didn't jive with the labels either. Finally I found a GMA 347 manual and  the nomenclature looked to nearly match  between the wiring diagrams and the labels. A quick email to Tony got a quick reply with a nice pic of  the terminals on the jacks and a PDF file  of the actual install guide for the audio panel. With all the information I have at hand, I think I can figure out how to solder everything up.

Where to put the jacks is the next problem. I don't want to jack into the panel, I'd prefer to have the cables off to the side, preferably the right. I don't have any side panels installed yet, so there's nothing there. I'll probably just mount the jacks temporarily somehow and fit them into a side panel later, maybe after some upholstery.

In the mean time, I drilled a nice big hole under the canopy rail outboard of the keyed switch at the right side. I put a grommet on the two cables and then drilled the next bulkhead. That was tough, fitting the wires though that channelized "beam". More grommets and were ready to go. I left the pilot wires dangling near the windshield bow and concentrated on the rear seat cables. I decided to run them though the triple beams amidships. A nice long spade bit works well here. Since there is that big plate there for the seat back brace, it was necessary to run the cable down a bit. Since the cable was a fixed length, it was tough to keep the wires hidden. Shoulda asked for an extra foot on both wires!

Almost time to solder the wires to the jacks. Tony came back with a nice little explanation of the wiring terminology (although he warns some manufacturers reverse TIP and RING):


And he shared this photo for clarification of wiring the jacks (the image below from Chief Aircraft):

Jack Wiring

Ok, I think I'm good to go. Time to drill jack holes and warm up the soldering iron.


The radios don't come with antennas (exception: GPS antenna with GNS480). So I figured out what all I needed and made an order with Aircraft Spruce. I already bought some RG400 cable, but no BNC connectors, so I ordered some of those, too. I hope my friend Jeff Tucker can help me crimp the cables and install and test the radios. In fact he offered to actually MAKE me a couple com radio antennas. More on that later.

Note: Stark Avionics recommends a special splitter made by Garmin to use with a combined NAV antenna. That costs an extra $125 in 2007. Evidently the NAV signals interpreted by the Garmin radios is picky, so the Garmin splitter converts the signals to something more tolerable and usable by the radios.

AV-17The main COM antenna is your basic bent whip AV-17. I decided to hang one from the empennage belly just behind the elevator bell crank. That gives it a smaller ground plane, but gets it quite a ways away from all the other antennas and airframe parts. This is the primary com antenna and will probably be hooked to the Garmin GNS480.

AV-569The marker beacon antenna is a "boat" type AV-569. I installed this under the rear seat floor in the center bay not too far from the rear stick. It is offset to the right a bit, centered in the bay. I installed a 90 degree BNC male connector on the antenna so the RG-400 coax would not interfere with the control column.

The antenna is supplied with a foam gasket. The screws that come with the antenna are so short that you really can't get them started with the foam in place. I used Clear RTV as a gasket and tossed the foam.

AV-22The transponder needs to pick up DME, so I bought the AV-22 stick and ball type basic antenna. Maybe slows me down .32 knots over the low profile aerodynamic models. Cheap, simple. durable.

I installed this little gem directly under my battery isolate in the forward stick bay. That gets it back away from the exhaust and gives some clearance from the titanium gear legs, too.

NavAntennaAndShield.JPGThe NAV antenna is a combined VOR and Glide slope "whisker" antenna. I bought a CI-158C "V" DIPOLE VOR ANTENNA
. Most airplanes have the antenna up on top of the vertical fin. I'm putting it on the empennage under the horizontal stabilizer, near the tailwheel. That makes the cable run a little shorter and easier. It also lessens the likelihood of someone poking their eyes out. Hopefully it will also lend a cleaner look to the airframe.

I used a piece of .032 as a stiffener over this antenna inside the empennage. I used the doubler as a template and marked the holes on the belly of the empennage just under the LE of the vertical fin. The doubler is actually about 7 inches long and is shaped like a wide "U" channel.  The longer end goes forward of the antenna and will be used to attach a fairing for under the antenna. That fairing is also made of .032 and is more a stone guard than aerodynamic fairing.

The doubler was Gooped into place and screwed down overnight to fix it in position. It has two #10 nutplates for the antenna and a #8 nutplate for the front end of the fairing, which tapers roughly in a V. If I ever find my camera, I'll take a pic of the parts. Seems my camera grew legs and walked off somewhere around the end of our local air show.

BellyAntennas.JPGI ended up putting the 4 major store bought antennas in line along the belly. From front to back, the transponder/DME antenna is under the front stick bay below the battery isolator.

In the rear stick bay, offset to the right of the center belly splice is the marker beacon antenna. I used clear RTV to seal it to the belly instead of the foam strip supplied with the antenna.

The bent whip is just behind the bulkhead that holds the elevator bell crank. I sanded off all the paint under the supplied doubler to make sure and get a good metal contact for the COM. This antenna comes with a rubber gasket to seal under the belly.

The aft antenna is the VOR/GS/LOC antenna.

I used RG400 coax for all of these antennas. I originally bought 40 feet, then bought 20 feet more when I had to order twisted cable for the autopilot. Glad I did!  My  coax runs really aren't that long, but to be safe I'd recommend 60 feet of coax for Rocket antennas.

Spruce sells BNC connectors for the coax. I bought 10 males and 10 females as a guess to what I needed. I should have skipped all the females and bought 20 males. I probably won't need all 20, but I am getting a Garmin specific splitter  for the  two nav radios.  I don't know if that is a duplexer or quadruplexer, but either way, I have extra coax and BNC terminals.

A-33-small.jpga33.jpgThe GPSs come with their own antennas. I put them up on the glare shield. The GPS in the EFIS MFD is a small black plastic job common to automotive style Garmin antennas. The GPS antenna for the GNS480 is an A-33. It's an "active antenna" (big deal) and sells separately at some avionics shops for about $400. YIKES!  I was going to paint it (even thought it says right on the antenna DO NOT PAINT) when I thought I might be able to replace it for about $70. Maybe I'll just cover it with black felt until I get in the air and do some testing.

The Garmin A-33 antenna needs a TNC MALE connector for your coax. A  TNCM  crimp on terminal for RG400 is about $40 at Aircraft Spruce. Like I stated above, I am not going that route, I'm just putting on an adapter and moving ahead.

The Experimental Copper Tape "Strut Antenna"

***Note: Don't try this yourself at home, kiddies. Not yet, anyway. 

My friend and fellow EAAer Jeff Tucker has been helping me with my antennas on my plane. He's the chief engineer at a TV/Radio station, and has forgotten more about antennas and radios than I'll ever hope to know (let alone understand). We have been playing around with hidden antennas. The only places I can hide antennas on my Rocket are under the cowl and under the gear fairings.

The gear legs offer the longest dimension to install an antenna,  but are still fairly short and narrow for one of the "off the shelf" hidden antennas. So Jeff has been the true experimenter and has tried various configurations of antennas on the gear stiffener. We (well he, actually) first tried a quarter wave antenna of various configurations that worked fairly well. In that respect, "fairly well" was on the ground, testing with a pretty sophisticated test meters.  That says nothing about how the antenna will actually work in the air under normal service conditions.The radiation pattern of the antenna will surely be affected by the big titanium rod directly in front of it! 

Anyway, we (well, Jeff...)  finally changed the antenna on the gear leg damper to a half wave folded dipole (continuous loop) antenna that tested VERY well in the COM bands, with SWR of 1.1 centered on the band and 2.1 at the extremities. He was quite pleased with the outcome, and so am I. Even if it doesn't work all that well in the air, at least I learned something, and feel like a true experimenter (even though Jeff did all the work!).  In it's original form, the antenna did not have a balun, and that created some problems, but in testing the antenna on the ground just as an antenna, it looked very promising!

StrutAntennaAppliedTop.jpg  StrutAntennaAppliedBottom.jpg

The antenna is made from copper tape bought from a hobby shop. It is normally used with "leaded" glass. The tape was cut to 1 1/4" strips and taped into the square wave pattern in the pics. It is a continuous loop beginning in the middle of the wood damper and goes over/through both ends and along the backside of the stiffener. The joint between each piece is then soldered, as well as a piece of wire is soldered over (or through) the damper just to insure continuity. A piece of RG400 coax is stripped and soldered to the copper in the middle of the top side of the stiffener and the coax comes away from the copper at a 90 degree angle, then up along the braided stainless brake line.

StrutAntennaComplete.JPGAfter Jeff taped the coax on the stiffener for testing, we hooked up my hand held to the antenna and found reception in my hangar to be quite good. Even with the hangar door closed I was receiving planes on approach at over 10 miles away. Not bad! And of course, ground control at our airport could hear me transmit loud and clear. We never expected this COM antenna to be as good as a bent whip on the belly, but so far the ground test results are very encouraging.

Jeff notes that in the air and away from the ground, the antenna characteristics might be very good, but might end up very crappy. And that really says nothing about the antenna's ability to radiate. We both realize that there is a big hunk of titanium directly in front of the antenna dampening and blocking the signal directly forward

This antenna project was completed before the airworthiness inspection, and needed some flight testing. But both Jeff and I are very encouraged by the static ground test results, and are fairly certain this antenna should work well as a secondary or tertiary COM antenna.

I bought a bent whip antenna for the belly of the aircraft, and installed it to be sure and have one solid reliable COM antenna. But what the heck, this IS experimental aviation, so that's what we're doing! It's a very cool concept.  Fingers crossed.

All is not well in River City. The 300 ohm folded dipole antenna with a 50 ohm RG400 coax feed line had problems. Serious problems. Not that it didn't work, mind you. It's just that the antenna needed a balun to transform the balanced copper tape antenna to the unbalanced coax feed line. In the original antenna setup, the coax was not only a feed line to the antenna, but was actually acting as part of the antenna. It was in fact radiating energy back to the radio and also into the electrical system.

It was a little disheartening to press the trigger (transmit PTT) and watch all the gauges on the EFIS screens go crazy. Not good. Turns out that it also affected the engine RPMs dramatically, too. When I pulled the trigger, the engine seemed to quit. Unfortunately, I learned this on a test flight, not on the ground. YIKES!

Tucker fashioned a coax balun. Ideally, you want to transform the antenna at the feed point with a 6:1 balun. That simply is the 300 ohm antenna to 50 ohm coax ratio. Many ham operators have found that you can get by with a 4:1 ratio, just using a section of 50 ohm coax connected in a very specific manner and at a very specific shield length. Later I found out that you could also do this with a section of 75 ohm coax, which gives you that perfect 6:1 ratio. Problem is, that with a coax balun, the "bandwidth" is quite narrow. Let me explain (as best I can... I am NOT an antenna guy by any means).

An aircraft com radio uses frequencies between 118 and 136.975. Ideally, you would like the antenna to have an SWR of 1:1 throughout that frequency range. Without a balun, the antenna showed a decent SWR of 1.1 somewhere along the com frequencies. We "tuned" the length of the antenna to move that "sweet spot" of the best SWR to the middle of the com frequencies (127.00). Unfortunately, the SWR dropped off (actually got bigger)  to over 2 at either end of the frequencies.  So the farther away from the sweet spot you get, the less efficient the antenna is. I think most pilots would prefer to choose a sweet spot (the best part of the "broadband") at the lower end of the frequency range because most towers and approaches are probably in the first half of the com band. Anyway, that's academic, I wanted a good broadband throughout the entire com band.

With a coax balun added (and a few 43 ferrites on the coax for good measure), the radiation back and into the unshielded unprotected systems behind the firewall was eliminated. WOOHOO?  Not so fast. The downside was that a coax balun is more for narrow band antennas. So adding a coax balun eliminated the mismatch between the antenna and the feed line, but reduced the SWR to a VERY small portion of the com band. At some point (tunable by changing the length of the coax balun and the antenna) the best the SWR got was around 1.6 and it dropped off to over 4 less than 1/2 way through the com band. THAT was not acceptable. The antenna is going to have enough to contend with being behind the titanium gear leg (and very close to it to boot). Jeff went back to his drawing board.

Balun, Mark II

Jeff came to my hangar with a new balun. It was a ferrite core, wound wire pair balun. It is a broadband balun. There's not much information on the web about it, and the calculus it probably takes to configure one is way beyond me. But we can sure copy stuff in a heartbeat, then tweak it to meet our needs. Again, between the antenna and the coax feed line we ideally need a 6:1 balun. You can get baluns all over the place. They usually come in a 2 inch piece of PVC and have huge eye bolts sticking out of them for HAM antennas that put out 1500 watts. NOTHING out there for a mere 8 watt aircraft radio. So Jeff made one.

Tucker soldered up the wires according to his diagram copied from one of the myriad radio and antenna references he's accumulated over the years. He tested it with the meter that checks the SWR and the "broadband". His eyes got big: "ONE TO ONE!" He was pleased. And after a little more testing he found out that the balun was indeed a broadband unit, the SWR was under two throughout the com band! SWEET!  

I fired up the batteries and waited for the EFIS to boot. Keyed the trigger, and barely a blip on the engine gauges on the EFIS. That was promising. Jeff tweaked the length of the antenna to tweak the band width position a little more. The EFIS showed a little more data distortion. Hmmm....

Another test that Jeff does is to check how much power is coming out of the radio via the feed line, and how much is going back. The radio was putting out it's full power, and only on the order of 150 milliamps coming back at the sweet spot, and upwards of 1 amp at the outer ends of the bands. We think the radios are capable of handling this much power reflected back through the coax. Radios have a "fold back" feature built into them. The radio senses how much power is coming back into them from the antenna and can power itself back to keep the antenna from harming it's electronics. Earlier in testing, the antenna was putting a full 5 watts back into the radio and it seemed to contend with it (for short durations). That's something we don't EVEN want to test for any length of time. We were all pretty happy with the return power in the milliamp to under an amp range.

Flight testing went well. The tower could hear me, and I them, clear as a bell. However, when I keyed the mic, I could see the EFIS data change a bit. Also, regrettably the engine RPMs dropped slightly. That's not good. I immediately landed, gave Jeff the bad news and we went back to the drawing board.

The SL-30 that is my secondary radio on the experimental tape (strut) antenna is pretty hearty. The GNS 480 that is my primary and hooked to a belly whip antenna is a little more fussy. However, it's up and running. At least as we test the experimental antenna, I can use COM 1 and not worry about RF, reflected power and the engine quitting when I want to talk to someone.  

The antenna experimentation continues. Jeff is ordering some more ferrite cores, doing some more research into winding a 6:1 balun that will fit under the gear leg fairing. Can't wait to see what he comes up with next!

TruTrak Digiflight II VSGV

DigiflightII.jpgThe autopilot I chose is the TruTrak Digiflight II series. This autopilot does GPS control wheel steering and has altitude holds. Since it's going to be hooked to the GNS480, it should be able to control the Rocket through holds and even ILS approaches. It should also take commands from the GRT EFIS, which has a WAAS enabled GPS.

I ordered the servos for pitch and roll about 3 years before getting the controller "head". I installed the cables provided with the servos early in the fuselage construction phase. Those servo cables were quite a bit shorter than they needed to be, and terminated in a 9 pin D sub connector. Now I know why. The TT AP head has a 25 pin D sub connector on the back, not two 9 pin plugs like I thought it would. So it really didn't matter whether or not I put the D-subs on the cables or not. In fact it might have been better to just leave the forward wire ends bare and soldered wire connections to the new cable to the head (which is not provided). Stein Air sells a 7 wire cable with two 20 gauge power/ground wires and 5 each 22 gauge signal wires. That's what I'll connect to the servo cables under the floor and run up to the big plug on the AP head.


The head is the original round type. TruTrak Flight Systems also makes a rectangular head, which I might have been able to squeeze over the top of my Garmin stack. However, I decided to just use the 2.25 inch round display and put it on the left side of my panel.

The wiring of the 25 pin connector looks quite complicated, but it isn't. The wiring diagrams provided by TT appear to be quite complete and the instructions straight forward. Another of the multitude of Rocket projects that will require me to read and re-read manuals about 10 times.  :-)  In actuality it was pretty easy to wire up. When you do a Digi II install on a Rocket, the instructions say you may need to reverse the pitch or roll servo actions. On the Rocket you have to reverse both. You do that by soldering a jumper on pins 1 & 2 on the DB25 plug (for the pitch servo) and then reversing two wires as shown in the instructions to reverse the action of the roll servo.

The autopilot requires a static line input as well as a Pitot line input. I T'd off of both lines going to the AHRS. The TT installation manual warns that if your autopilot seems to hunt or wander a lot in the air, there may be insufficient static vacuum. If the autopilot acts up, it might be necessary to run a separate static line just for the AP. Or you might want to splice a line to the AP very near the actual static ports in your ship. Just a heads up.

The autopilot requires a 5 amp breaker. I'll put a 5 amp rocker breaker in the panel for AP shut off. You can also wire a shut off to a stick grip. In addition you can turn off control wheel steering using a momentary switch on the stick or any other remote location. The main power switch/breaker also powers the servos. The control head only uses about .5 amps and each servo uses about 1 amp.

When I was "ground testing" the autopilot before first flight, I turned on the autopilot at the rocker switch and went through the functions step by step in the instructions. Most of the settings in the AP stay set as per the factory (at the beginning at least). I did increase the torque from 2 to 8 on the roll servo, otherwise I think I left all the other settings the same.

Note1: Testing of the control wheel (stick) steering in my plane showed that the roll servo on the ailerons needed to be reversed. IOW, when I rotated the "enter button" to the right (clockwise), the stick went left. So it was necessary to shut down, pull the DB25 pin plug and reverse two wires (I believe it was 18 and 19, but I'm not sure).

Note2: I soldered in the pitch servo jumper on the pin plug and I'm happy to report that I DID NOT NEED TO. The jumper is NOT necessary for the Rocket TT pitch servo. The action of the servo by the Digiflight does NOT need reversed. Just leave the #1 and #2 pin slots empty.

The servos have step motors in them. I didn't realize that would make the stick move in steps. Actually the ground action on the stick by both servos results in motions that are pretty jerky. I hope it feels a lot smoother in the air. But when the AP face lit up for the first time and the stick moved with turn of the knob, my face lit up too. Building this plane is a series of small accomplishments, and seeing the autopilot work for the first time was a biggy!

Headset Jacks

Not a very glamorous topic, but important none the less. Where to put the jacks out of the way took a little consideration. I like where they were on my Decathlon, up over my head and behind me. I would have done this with my rocket, but alas, it has a sliding canopy. And since the wire runs from my audio panel were somewhat short and shielded, I decided to stick them up on the cabin rail, just in front of the windshield bow. For the passenger jacks, I stuck them in the aft triple beam on the side wall of the ship.



Avioncs Configuration

My GNS 480 failed within 10 hours of flying time. What I figured out when this happened was that A.) I had the EFIS incorrectly configured and B.) the autopilot would not function without the GNS 480 working as I had it configured. To correct the problem, I made some changes that I thought I'd share.

The EFIS Internal GPS
I have the GRT internal WAAS GPS installed in DU2. It must be set at 4800 baud, both input and output, and my understanding is that you CANNOT use those serial ports for any other accessory or avionics. Once I set the RS232 serial port 1 (in and out)  for the GPS as GPS2 and 4800 baud, it worked beautifully!

The ARINC 429 Module
This steering command gizmo resided in DU1. Carlos at GRT assures me that the corresponding serial port #1 pins CAN in fact be used for other uses. I think my avionics shop had me wire these ports to the GNS 480.  Now, the ARINC module has it's own input and output wires on a 9 pin connector. Carlos recommended that the settings used under the ARINC setup in the GRT unit be configured as HIGH for receive and LOW for transmit. I'm not sure about those settings. I think to keep everything on the down low, I'll set everything but the internal GPS to LOW and 9600 baud.

The Data Source Switch
When my GNS 480 failed, I lost autopilot function. Since I didn't have the internal GPS configured properly, I thought without the 480 funcitoning, I couldn't use my autopilot. That's not necessarily correct. However, just to be sure, I split out the data wires for the autopilot to make the GPS sources to the AP physically independant. That means I needed a 3PDT toggle switch, with three wires from each source to the toggle, then onto/into the AP's appropriate 3 pins. Now, in the GRT unit, if you merely switch your NAV source from GPS1 (480) to GPS2 (EFIS), the autopilot should track whichever NAV source you have selected. At the time, I didn't trust the internals of either source, so I hard wired them to the autopilot independantly. Now there's no question which system is steering the plane, and if one source fails, I can manually switch to the other.

The Autopilot only gives you the choice of one baud rate. I chose 9600 and had to make sure the output from the GNS 480 and the EFIS GPS was 9600.

GRT Horizon 1 EFIS Configuration

Here's a table of how I have my Dual Display Unit, single AHRS, with ARINC 429 module and internal WAAS GPS configured:

RS232 Serial Port Input Pin # INPUT Source Baud Rate Output Pin # OUTPUT Source Notes
DU1 - Port 1 A20 (**ARINC)   SL30 9600 A2 (**ARINC)   SL30 SL30-2; SL30-2
DU1 - Port 2 A19 AHRS 19200 A4 AHRS AHRS; AHRS
DU1 - Port 3 A23 Inter-Display 9600 A25 Inter-Display  Display Unit Link; Display Unit Link
DU1 - Port 4 A21 EIS 9600 A5 off     (1)  EIS; off
DU1 - Port 5 A22 GNS 480      9600 A3 Autopilot Aviation/MAPCOM; GPS1 NMEA0183
DU1 - Port 6 A24 off 9600 A1 Alt Encoder off;  Z Format
DU2 - Port 1 A20 Internal GPS  4800 A2 Internal GPS Cannot wire pins
DU2 - Port 2 A19 AHRS 19200 A4 AHRS AHRS; AHRS
DU2 - Port 3 A23 Inter-Display 9600 A25 Inter-Display Display Unit Link; Display Unit Link
DU2 - Port 4 A21 EIS 9600 A5 off EIS; off
DU2 - Port 5 A22 off 9600 A3 Autopilot off;     GPS2 NMEA0183
DU2 - Port 6 A24 off 9600 A1 Alt Encoder  off;    Z Format

* If you have dual Display Units, the sources listed in BOLD are factory determined and should be configured as set.

* All RS232 ports must match baud rates at both ends of the wires, I.E. the GPS data to the autopilot typically BOTH units must be configured to 9600 baud.

* The internal GPS as provided by GRT is a 4800 baud unit, and if it is installed, the serial ports cannot be used for other functions. Set input and output to 4800.

** The ARINC 429 module does NOT use up the RS232 ports and they can be used by other functions. You have to tell the GRT EFIS that the ARINC module is installed by indicating YES in the setup.  Since I have a TruTraK Digiflight II VSGV, the ARINC transmit settings should be set to LOW.

(1) It is recommended that output from RS232 port 4 go to the GNS 480 and the GNS 480 set to FADC on that "channel".

GNS 480 Configuration

Since they discontinued selling the GNS 480 in December of 2007, I don't think many of you will be able to take advantage of my sample configuration. However, for my own "archival" purposes, I'm going to list how my 480 is configured, particularly with regard to the RS232 serial inputs.

CH RX Baud TX Baud
1 FADC 9600 MAPCOM 9600
2 NONE     (CNX80³) 0 NONE    (CNX80³) 0
3 NONE     (IRDA¹) 0 NONE    (IRDA¹) 0
5 SL30 9600 NONE 0
6 GTX32 9600 GTX32 9600
7 NONE     (COG²) 0 ------ -----
8 NONE     (ALT ENC*) 0 ------ -----

¹    If you use an infrared receiving PDA or similar device, you can turn on the IRDA and  TX, RX at 19200. Supposedly not currently supported.
²    If you want to have a CO monitor, the CO GUARDIAN  can be wired to the 480 to give warnings if CO2 limits get dangerous.
³    You can have dual GNS 480s (CNX80s) wired together at 38400 baud.
*    A stand alone blind altitude encoder can use this serial port at 1200 or 9600 baud.

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