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It's been a busy week. I spent the week in Orlando at an Enhanced Visions Systems conference (i.e. infrared camera which provides a view in a heads up display so the pilot can see to land in thick fog). I managed to find some time to visit Bernie Kerr, who took me in a ride in his RV-6A, and gave me a tour of the air park he lives on. Very nice set up. I'm jealous.

Yesterday I took care of a bunch of odds and ends. Today was the second nice day we've had this spring, and it has snowed twice since the last really nice day, so Terry and I took full advantage of this one. We went for a long walk, sat outside to drink coffee, etc. Late this afternoon I attacked the RV-8 project again.

I modded the mount for the Navaid wing leveler to make more room for a wire bundle, then primed the parts for the mount. Then I checked out the GNS-430 com transmit, using a VHF scanner to listen. The transmissions were extremely broken, but I think perhaps the 12 volt power supply I am using doesn't have enough juice. At least I really, really hope that is the explanation. I need to get a decent 12 V battery to power things to try again.

Then I redid the calibration of the CDI course, as I noted a consistent 1° error between the course that was displayed on the CDI, and the course sensed by the GNS-430. And I confirmed that the GNS-430 and the transponder were talking to each other - I thought there was a problem, but I once I went into the maintenance pages I could see that the transponder altitude data was being seen by the GNS-430.

A couple of other builders were interested in some details of the SD-8 standby alternator installation, so I posted a few pictures of it in the Construction Photo Gallery.

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My wingtip NAV and COM antennae arrived yesterday. I don't like giving away speed to unnecessary drag, so I want to have as few external antennae as possible, while still having acceptable antennae performance. The transponder antenna and one COM antenna will be external, on the belly. The GPS antenna will be under the canopy, and the NAV and second COM antennae will be in the wingtips.

Bob Archer Com and Nav AntennaeBob Archer has built up a reputation for producing antennae that have excellent performance. You would think that the NAV antenna wouldn't work so well if the VOR station was on the other side of the aircraft, but everyone that has one of these antennae says that they get good performance no matter where the VOR station is. Builders have reported reception ranges in excess of 100 miles, which is more than enough.

More info on Bob Archer's antennae is available in an article he wrote, and in the a product review on Sam Buchanan's web site.

VOR signals are horizontally polarized, so the antenna needs to be horizontal, which means the wingtip is a good choice, as the antenna can be placed against the large flat top of the tip. VHF COM signals are vertically polarized, which means the antenna needs some vertical development in order to work. The wingtip is only about 7.5 inches deep, so that limits how much vertical development that antenna will have, and performance will suffer. Still, builders are reporting reception ranges around 50 miles, which is good enough for COM 2. I'll check the performance after I get flying, and if I am not satisfied, I'll add a second COM antenna on the belly.

Bob Archer is an incredibly laid-back guy to do business with. He doesn't take credit cards, and he didn't want any money up front. You place your order, and he ships the antennae with the invoice. You send the money after the antennae arrive.

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The problem with the PTT wiring has been really bothering me. One of the cats managed to wake me up Sunday night, and I laid there in bed for three hours stewing on the problem. Pondering the various possible causes of the problem, deciding how I could rule out each possibility, and planning the easiest way to fix each possible problem. As a result, I didn't get near enough sleep, and was too tired and depressed to attack the problem Monday evening.

I slept well last night, and this evening I planned to methodically attack the problem. I figured I would probably have to disassemble the stick grip, so I put the cockpit floor and front seat back in, as I needed a place to sit while I worked. Then I took another close look at the wiring. After studying it a while, I noted a black wire that was routed in the main wire bundle, but wasn't connected to anything. I followed it back, and it went to the wire bundle that came from the stick grip. I connected the ohmmeter to it, and the other wire that was supposed to come from the PTT switch. I pressed the PTT switch on the stick grip, and the ohmmeter showed that the circuit had closed. Bingo!

What a sense of relief! My wiring is OK after all! I just needed to find the right wire. No tearing the stick grip apart and then trying to get it back together again. It was a very difficult job getting it assembled when working on the work bench, and I could rotate it to any position I wanted. It would be an extremely difficult job trying to do it with the stick in the aircraft. And I can't remove the stick without either tearing all the wiring out, or cutting the wiring harness and splicing it later.

Now that I knew the PTT switch worked, I took some jumpers and connected it up to the PTT wire in the audio panel harness. I was able to determine that each Com radio transmits upon command. Now I need to get Jim Manton over to transmit while I listen on the VHF scanner.

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This afternoon I finished my taxes (due the end of April in Canada). This evening I went into the garage, intending to hook up the Push-To-Talk (PTT) wires to the audio panel harness and test out the transmit functions, using a borrowed VHF scanner to listen while a neighbour pilot transmitted. Should have been a quick job. However, it seems there is some kind of problem with the system. I puzzled around for a while with an ohmmeter, but it is looking more and more like the PTT switch buried in the stick is bad, or disconnected.

I really, really don't want to have to open the stick grip up, as it was a royal pain in the you-know-what getting it installed on the top of the stick. So, I spent quite a while chasing down any possible alternative. There was a chance that the problem was I had mixed up two of the wires coming out of the stick grip, but I checked all other functions, and they work correctly, so they must be using the correct wires. The process of elimination only leaves two wires, and they are the correct colours, and nothing happens when I push the PTT button with the ohmmeter connected to them. Blast!

I gave up in disgust and I'll take a fresh look at things tomorrow.

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We had company staying with us most of the week, so that pretty much killed any time I had to work on the aircraft. Terry left today for a week on the road, so I wanted to spend time with her on Saturday.

What little building time I got in before today was spent on running a few more wires for the electric pitch trim. I spent way too much time trying to find a good routing for a couple of those wires.

I also started thinking about the four annunciator lights I will have. I hadn't considered it before, but I realized that I should come up with a way to dim those lights for the times that I fly at night. Each of the lights is controlled by power that is switched to put the light ON or OFF. I couldn't come up with a simple way to dim these lights, so I posed the question to the Aeroelectric-List. Bob Nuckolls suggested using a zener diode that would be switched into the common ground of the lights. This would reduce the voltage drop across the lights, but it would only give a single fixed level of dimming. I would also have to experiment to find the optimum value of the zener diode.

A helpful guy from Finland suggested another solution, using a PNP transistor as a "transistorized negative voltage emitter follower" (his words, not mine). This way I could use a potentiometer to control the intensity of annunciator lights. We exchanged several e-mails to discuss details of the circuit, and eventually he came up with an interesting option to use a SPDT switch ON-OFF-ON switch to give three operating modes: Full bright, Dim (intensity controlled by the potentiometer) and Auto (full bright if the position lights are OFF, and dim if the position lights are ON). I picked up the components a couple of days ago, now I need to assemble the prototype to try it out. If this works, I'll post the circuit diagram once I've sorted it out.

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It's been a busy week, but unfortunately not much of the activity has been on the aircraft project. Tuesday I hooked up the Microair 760 com to the under-fuselage antenna and the audio panel. It receives the ATIS nicely. I still need to track down a handheld VHF to confirm both radios transmit OK. I thought I had a problem with the mic from the rear seat, so I pulled the audio panel harness back out to give it another wring out with the ohmmeter. It was fine, and it worked perfectly when I put it back in the aircraft. I think the problem could have been that one of the DB-25 plugs wasn't fully engaged on the back of the audio panel.

Then I was in Montreal for a few days - I got back late Saturday afternoon. The correct switch for the rear seat pitch trim arrived while I was away, so today I installed it. The switch for the pitch trim power in the front cockpit has three positions: OFF, Front Seat Only and Front and Rear Seats. That way I can disable the rear seat trim switch when I have a none-pilot in back.

I spent quite a while today working my way through the multitude of configuration setup pages on the GNS-430 and GTX-327. There are dozens of options to set to tell the units what inputs and outputs they are dealing with. I realized a while ago that the GNS-430 wasn't receiving altitude data from the transponder - it turns out that this is one of the options that must be set. I had also been concerned about a 5° error in the CDI course output - there is a configuration page that allows you to calibrate the CDI input, so now the error is less than 2° everywhere.

And then I spent quite a while puzzling over annunciator dimming. I've got four LED annunciators that I need to deal with. All will be unlit most of the time, but they could be illuminated for long periods if they are annunciating a system failure. All of them are driven by a 12V signal when they are in the ON state. I.e 12V = ON, 0V = OFF.

Read on for the rest of the story.